October 24, 2023 • 56 mins
In this episode, Peter Dragic, of the University of Illinois, Urbana - Champaign, shares his expertise bridging a gap between next generation laser sources and active sensing systems such as LIDAR. We'll journey together through the captivating world of LiDAR, shedding light on its applications, complexities, and potential future paths.
Our exploration begins with a look at how this cutting-edge technology is being used in diverse fields such as automotive, surveying, mapping, and archaeology. You’ll gain insights into the challenges of crafting high-power lasers for LiDAR systems, and the pivotal role of laser alignment in ensuring accurate measurements, for example.
Host:
Akhil Kallepalli
Leverhulme Early Career Fellow
University of Glasgow, UK
Moderator:
Rajesh Menon
USTAR Professor
University of Utah
Expert:
Peter Dragic
Associate Professor
University of Illinois, Urbana - Champaign
Have a topic you're interested in hearing about? Let us know!
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Transcript
Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
Speaker 1 (00:00):
are finalized, but we'll send you the episode as
soon as it's edited, just so youcan review it and kind of give
it the final approval.
I don't imagine you guys aresaying anything.
We shouldn't, but just in caseyou wanted to listen really
quickly and spot-track it, oryou listen to it.
Speaker 2 (00:19):
You mean you'll give us the veto power if we say
something controversial.
Speaker 1 (00:27):
Yeah, we actually can .
We want you guys to be proud.
Like you said, you wanted toput it on your social media.
We definitely want youencourage you to be proud of the
episode and our editor isreally good.
So if we want to changeanything, we can.
The only thing we can't changeis the intro song, which is very
fun.
You guys will hear that.
But, yeah, we can edit anythingthat happens in the episode
(00:50):
which goes into what I'm goingto say next.
This is really relaxed.
If you start to answer aquestion or start to ask a
question and you feel like youkind of misspoke or didn't say
it how you wanted it to come out, feel free to say I'm just
going to do that again and we'lledit it out.
We're not on live TV, nothinglike that.
(01:12):
So this is really relaxed andthe editor has a really good eye
to fix anything if somethingdoesn't flow right.
So if there's no otherquestions, I will pass it off to
a kill the host to kick it off,and, feel free, I'll be on with
you guys the whole time.
So if I hear something that Imight say, oh, let's redo that,
(01:34):
I might pop in, but likely not,because we do want it to be
organic, but if you have anyquestions that arise during the
conversation, I'll be here, orany technical questions.
Speaker 3 (01:45):
All right, excellent, peter Rajesh ready.
Speaker 4 (01:50):
Yep sounds pretty good Excellent.
Speaker 3 (01:53):
So in three, two, one .
Hi everyone and welcome totoday's episode of Illuminated.
I am Akhil and, as theAssociate Vice President of the
Young Professionals and theChair of the Young Professional
Advisory Committee, it's mypleasure to be your host today.
I'm a biomedical physicistmyself working at the University
(02:16):
of Glasgow as a leading humanearly career fellow.
In my role for the IxativeEthnic Society, I'm supporting
and promoting initiatives verymuch like this podcast, to raise
the profile of valuable youngprofessionals within various
sectors.
The Young ProfessionalsInitiative is for graduate
students, post-doctoralcandidates and early career
(02:37):
professionals up to 15 yearspost their first degree.
This affinity group within theIxative Ethnic Society is
committed to helping one pursuea career in photonics.
We're here to one help evaluateyour career goals, to better
understand technical pathwaysand subject matters, refine
skills and finally growprofessional networks through
(03:01):
mentorship.
Now onto the more exciting ourpodcast for today.
Today is a particularlyinteresting topic that we're
talking about.
Working in classical andquantum optics myself, and with
a keen interest in time of lightimaging and sensing, our topic
is of a particularly personalinterest to me.
We're discussing LiDAR systems,technologies and current
(03:24):
questions regarding the state ofthe field and the future of the
field itself.
Our very special guest,professor Pete Dragitch, and
moderator Rajesh Menon, are herewith us.
We're going to technology,career journeys, advice from
within and beyond research.
Now, firstly, thank you verymuch for listening to this
(03:45):
episode.
I am already certain it's goingto be a great one, and I hand
over to Rajesh for the nextintroduction.
Speaker 2 (03:56):
Great Well, thank you , O'Kill.
I'm very excited to be herewith both of you.
We are honored to have PeteDragitch as our expert for today
.
Speaker 3 (04:15):
Sorry, I know Kristin's already listening in.
Could I just go back?
Until?
When I actually finished aboutthank you for listening to this
episode, I realized if I justscroll the page, I'm doing the
introduction for Rajesh as well.
I'm going to do theintroduction for Rajesh and then
I'll hand over to Rajesh again.
Speaker 1 (04:34):
Okay, perfect, good catch.
Speaker 3 (04:36):
Yeah, I mean literally scroll.
Speaker 1 (04:41):
Okay, go ahead, you can just pick up from there.
Speaker 3 (04:43):
Yeah, I'll hand over to Rajesh again in a second.
Speaker 1 (04:46):
Okay, perfect.
Speaker 3 (04:49):
All right, three, two , one.
I will now hand over to Rajeshfor the episode and for
conversations with ProfessorDragitch.
Rajesh Menon is an engineer andentrepreneur advancing
knowledge at the intersection ofoptics, nanofabrication and
computation.
He is a professor in electricaland computer engineering at the
(05:12):
University of Utah, a fellow ofOptica, sbie and a senior
member of our very own IEEE.
After receiving his PhD fromMIT, he co-founded and led a
spin-off company forcommercializing maskless
lithography.
His lab in Utah is exploring amultitude of imaging systems
(05:33):
enabled by nanofabrication andcomputational methods, including
miniaturized endomyroscopy fordeep brain imaging, ultra
lightweight optics for airborneimages, computationally enhanced
diffractive spectral images andmany, many more.
Rajesh is also invested in thesuccessful realization of
laboratory innovations byentrepreneurship and his funnel
(05:57):
for companies.
It is a great pleasure now thatI hand over to Rajesh for the
rest of the episode.
Take it away.
Speaker 2 (06:08):
Great.
Thank you very much for thekind introduction, Akhil, and
it's an honor to be in this finecompany and very excited to
talk about a very pertinenttopic, which is LIDAR.
It's the topic of this podcast.
Lidar, of course, stands forlight detection and ranging.
(06:29):
It is a remote sensingtechnology that uses lasers to
measure distances and many morethings about the 3D environment
which we will learn about today.
Most of us have somefamiliarity with automotive
LIDAR.
In automotive LIDAR, laser beamis emitted from a source and we
(06:54):
measure the time it takes forthe beam to bounce back off from
objects in the environment.
This data is then used tocreate a detailed 3D point cloud
of the area being scanned.
What is really exciting now isthe creation of 3D point clouds
(07:16):
such as automobiles, butincluding surveying, mapping,
forests, urban sprawl,archaeology, environmental
monitoring, etc.
It's a very exciting technology, but just getting very wide
usage, which is, of course, thegoal of almost any technology
that comes out of the lab.
(07:37):
Today we are honored to have anexpert in the field of LIDAR,
Professor Peter Dragic, with usto geek out about LIDAR.
Pete received his PhD from theUniversity of Illinois at Urbana
, Champagne in 1999.
After a stint doing startups,he returned to his alma mater,
(07:58):
where he is currently anassociate professor in the
Department of Electrical andComputer Engineering.
His graduate work focused onthe development of fiber
laser-based sources foratmospheric LIDARs, namely for
the sensing of water vapor.
His current research interestsrange widely from optimal
materials to lasers and lasersystems, including LIDAR.
(08:20):
A particular interest are fiberlaser systems, which offer some
advantages over theircounterparts.
However, they also suffer moresignificantly from power
limitations due tononlinearities.
Therefore, much of Pete'sattention has also been focused
on reducing the impact of thesenonlinearities, and optical
fiber systems for applicationssuch as remote sensing.
(08:43):
The first of two current LIDARprojects is an upper-demospheric
slash exospheric LIDAR for thedetection of metastable helium.
The other is the sodium LIDARthat will take a ride on a
sounding rocket through thelower to middle thermosphere.
It is my distinct pleasure toinvite Professor Pete Dragic to
(09:05):
this conversation.
Pete, let us start with anintroductory question about
could you share with us how youchose to get into the field of
LIDAR and what inspired you topursue these topics?
Sure thing, Rajesh.
Speaker 4 (09:20):
Thank you very much for the kind introduction.
I'm also very pleased to behere in the company of some
really wonderful people, somegreat minds.
To answer your question, Iguess this goes back to my
undergraduate days.
During the end of my junioryear I was looking around for a
summer undergraduate researchexperience pretty much of any
kind.
Frankly, I wasn't sure ifgraduate school was for me or
(09:44):
not, but I was fortunate to finda faculty member working on
semiconductor-based LIDARs whowas also looking for
undergraduate researchers.
At the time.
His group was trying to developa system to measure atmospheric
water vapor concentrations.
Water vapor turns out as a verystrong and indeed the most
abundant greenhouse gas.
It helps to trap radiation,keeping thermal energy from
(10:05):
escaping the earth's atmosphere.
Some of us understand that tobe a source of global warming.
Anyway, I spent a summerworking on the laser transmitter
and became passionate aboutlasers and, frankly, I've been
at it ever since.
In fact, I became a graduatestudent in the same group where
I did my undergraduate research.
(10:26):
I also had a NASA fellowshipduring my graduate days from the
Goddard Space Flight Center,helping with a similar system,
actually for the Martianatmosphere.
The goal there was to look forterrestrial vents of water vapor
that could be indicators of thepresence of things like
microbial life.
What's neat about LIDAR andthis is kind of what keeps me
going is, if you like lasers,for every LIDAR that you build,
(10:46):
you get to build a new kind of alaser system, and so I think
that's really really neat andvery exciting.
Speaker 2 (10:57):
Wonderful.
Thank you, pete.
It's quite instructive that youwere inspired by an
undergraduate researchexperience, which really
underscores the importance ofsupporting and mentoring
students, which I think we'llcome back to later in our
conversation, and I'm alsofascinated by your PhD work
(11:23):
about detecting water vapor inthe Martian atmosphere.
Clearly, it would be one of thegreatest discoveries of human
history if we were to detectproof of extraterrestrial life
forms even outside of solarsystem.
This is something I would liketo come back to as we go through
(11:46):
this conversation, but let usbegin with something more down
to earth.
Could you give us an overviewof what your group is currently
working on, the technologiesyou're developing and their
exciting applications that theywill enable?
Speaker 4 (12:03):
Sure thing.
I'll speak to the two lidarsthat we're developing in our
group, both of which are typesof lidars known as resonance
fluorescence lidars.
So the way that they work isone pixel laser beam tunes its
wavelength to an absorptionfeature of a species.
(12:23):
In the case of our systems theyare helium and sodium.
Those end up being actually inthe upper atmosphere.
There's a layer of sodium,roughly 90 to 130 kilometers up,
that resides there due toablation of mainly meteorites as
they come into the earth'satmosphere.
(12:43):
And then helium, in the upperatmosphere ranging from about
300 kilometers to about 900kilometers.
There's a layer of helium, Ofcourse.
What can imagine if theatmosphere stratified?
The lightest element willappear at the top.
And so what we do there?
Basically, the principle behindresonance fluorescence is,
again, we tune our laserwavelength to an absorption line
(13:07):
, like the D2 line of sodium,for instance, at 589 nanometers.
That species will absorb thatphoton and then re-radiate it.
It'll re-radiate it asfluorescence and therefore it
goes in all four pi-stradians,all directions basically, and
we're looking from somewherelike the ground or from
somewhere where we have atelescope, the helium lidar.
(13:28):
The goal is to measure out toroughly 900 kilometers, 1,000
kilometers metastable helium.
So what happens there is thatsolar radiation comes in and
that energetic particles arecreated, collide with the helium
and excite those heliums intoan upper state, Many electron
(13:49):
volts above the ground state.
Once you're up there, there's afeature, an absorption feature
at roughly 1 microns 1083nanometers actually that can be
used to probe the presence ofthat metastable helium in that
part of the atmosphere, and soof course we want to make sure
our laser wavelength is at 1083nanometers.
What's interesting about thisis that's a wavelength that's
(14:11):
achievable through fiber lasertechnologies, among other solid
state methods, and what we'reinterested in doing is creating
a high power source that can goup far enough into the
atmosphere.
Again, it's a resonancefluorescent system.
So then that laser signal willbe absorbed, It'll be
re-radiated to the ground and wesit on the ground with a very,
(14:34):
very large telescope, such as anobservatory telescope or
something like this, and receivesignal back Again.
If we do, if we pulse the laseror we can actually do other
techniques to sort of do rangeresolution, and we can track and
we can watch the helium, thatmetastable helium concentration,
as a function of time anddistance, and that gives us
(14:55):
information about the dynamicsof the atmosphere.
So the helium itself serves asa tracer.
It's not necessarily that wecare to first order about the
helium itself, although thereare interesting things about
that too.
It serves as a tracer to giveus details about the atmospheric
dynamics.
That second system is asodium-based system, Again at
(15:16):
589 nanometers.
That one is not directlyproducible by a fiber, but again
you start with some sources andyou get to a wavelength
somewhere in the infrared andyou do frequency doubling and
there's lots of neat ways toachieve that wavelength.
But anyway, the idea is thereis a layer of sodium roughly 90
to 130 kilometers, and watchinghow that sodium moves through
(15:39):
the atmosphere gives usinformation about atmospheric
dynamics, the motion of energyfrom lower parts of the
atmosphere to the upper parts ofthe atmosphere.
How do they couple?
A lot of that is still notunderstood by humanity, and
understanding the way thatfunctions can give us better
insight into creating globalenergy transport models for our
(16:00):
planet.
The idea there, of course, thesystem itself will take a ride
on a rocket.
What we're looking for inparticular for that system is
kind of a short-range, rangingfrom the rocket, say, a couple
to a few kilometers, and we'relooking for turbulence effects,
mixing effects.
So what happens during mixingevents.
(16:23):
We're simply using the sodium,again as a means to watch that
process.
It's not so much that we carehow much sodium there is.
Again, there are reasons whyyou'd want to know how much
sodium there is.
For instance, there are guidestar applications where
understanding the concentrationis very important, but we're
using that as a tracer toactually watch the motion of the
atmosphere.
Speaker 2 (16:47):
It's very interesting .
I just want to make sure Iunderstand it.
In the case of the resonancefluorescence, you are exciting
the resonance and watching thefluorescence from the ground.
How is the excitation beamscanned across some field of
(17:07):
view?
How does it actually work?
Speaker 4 (17:11):
We can scan the beam.
Most generally, though, wedon't scan the beam.
It's kind of a line of sight.
We look in one direction.
The beam will expand to someextent, of course.
Think about a milliradian beamgoing hundreds of kilometers.
It'll be a relatively largebeam, so we're really
integrating across its area.
Certainly we can think about ascan.
(17:31):
That becomes a little moredifficult as one goes to large
scan angles because the distanceto the measure end is a little
bit increased.
Speaker 2 (17:40):
In that respect, how do you actually get the range
information from where thefluorescence came from?
Speaker 4 (17:52):
For a LiDAR.
You can do this a couple ofdifferent ways.
The most common approach is touse a pulsed LiDAR, which you
alluded to earlier in thediscussion today.
What you do is you send out apulse of light.
You're basically measuringreturns as a function of time.
It's a time of flight thing.
If you get to some point intime where you start measuring
(18:15):
information, you could turn thatinto or start measuring returns
.
You could create a distancedistribution by scaling via the
speed of light.
Understanding there's a roundtrip involved.
One of the caveats there, ofcourse, is if you do a pulse
system, you want to make surethat your pulse goes out in a
way that you don't alias yourreturn signal from the
(18:39):
atmosphere.
That means that if you sendyour pulse out, you want to make
sure your pulse goes out andthen it leaves the line of sight
to make sure that you're notgetting returns from different
parts of the atmosphere, fromdifferent pulses.
Speaker 2 (18:54):
Ah, yes, yes, I see that was actually one of my
questions was would there bepotential for ambiguity if
sodium at different distancesacross the layer starts
fluorescing from the same pulse?
Is that very possible?
Speaker 4 (19:15):
Yes, it's possible, but because the pulse is
propagating at the speed oflight through that range, when
we receive those returns will bea function of time as well.
Speaker 2 (19:29):
So if we send out a pulse.
Speaker 4 (19:31):
Let's say there are two ranges, X1 and X2,.
Well, distance equals rate,times, time via the speed of
light, of course, and so when westart receiving signals from
the first part, from X1, will bea time different from X2, and
that's how we can resolve them.
But if we have multiple laserpulses that exist at the same
time, then it becomes ambiguousto you know which pulse
(19:54):
contributed from which layer.
Speaker 2 (19:56):
Yeah, yeah, yeah, yeah.
Very cool, and I would assumethat the signal that you receive
back is quite weak.
Can you comment on that?
Like, how much?
What's the efficiency from theexcitation to the received
signal?
And if that is a challenge, howdo you deal with it?
Speaker 4 (20:18):
Yes, that is a challenge actually.
You know you send out a signal.
That might be, you know, forour helium LiDAR we're actually
envisioning kilowatt lasers.
You know the return is going tobe many, many, many orders of
magnitude below what you put out.
Oftentimes it requires photoncounting and so you'll actually
have a receiver or a detectorlike a photomultiplier tube or
(20:40):
an avalanche photodiode orsomething that's configured to
count photons.
Of course that depends on thenumber of returns.
You know, if you have a largeramount of returns, you want to
make sure that your photoncounter can keep up with the
number of photons that arecoming back.
If your returns are very smallor very low the number of
photons, then we have toconsider, of course, ultimately
(21:04):
scaling the receiver design.
So you know, if our returns arelow, you know a couple of
photons such that they'reswamped out by the noise that we
might get, you know, say,thermal noise or background
light from some other source,then we think about scaling the
telescope, you know.
So it's kind of like the trickin LiDAR is power and aperture.
(21:25):
So the more power you have, ofcourse, the more returns you're
going to get, the more apertureyou have, the more of those
photons you can collect, youhave a larger light bucket.
There is, though, a limit tothat, especially in terms of the
residence fluorescence LiDARs.
The residence fluorescenceLiDARs, actually, I mean,
they're like it's almost like afluorescent material in space,
(21:46):
kind of like a laser, for themost part kind of up in the
atmosphere, and so you know, ifyou put out too much of the
laser signal, hoping to getreturns back, you can actually
saturate the layer, and sothere's going to be a limitation
, potentially, to how muchsignal you can get back,
regardless of the size of thetelescope.
Speaker 2 (22:06):
Wow, yeah, I was just noticing how many different
parts of electrical engineeringcome into play to make the LiDAR
work, everything from optics tosignal processing.
Speaker 4 (22:22):
Yes.
Speaker 2 (22:23):
I'm curious if I were to dig in a little deeper into
the laser itself.
You mentioned very highkilowatt lasers.
Could you talk a little bitabout the challenges and
complexity of building suchlasers?
Speaker 4 (22:40):
Oh, certainly.
Of course, the laser itself iscomprised of many components.
There's different ways toachieve laser technology.
One it could be based on itcould be a traditional laser
that's based on a resonator, and, you know, you kind of achieve
high power that way.
Other approaches are to createthese master oscillator power
(23:02):
amplifier type lasers, where youstart with a seed laser,
perhaps a relatively low power,and then you amplify it.
In fact, both of the systemsthat we're building are based on
that technology.
The helium LiDAR is nothingmore than a semiconductor laser
that's amplified by a chain offiber amplifiers, and then our
(23:26):
sodium system is based on Ramanscattering in bulk crystals.
In that case, again, it'samplifiers that are amplifying
our signal, and then at the endwe double to get the 589 from
1178 nanometers.
To get to the high power, thereare several things that of
course we have to think about.
One is you have to energize, orprovide energy to the laser.
(23:50):
So the pumps, as we call them,have to provide sufficient power
in a wavelength range that thegain material can absorb.
That's basic lasers 101.
And then you have to considerthe modality or the framework by
which you're actuallygenerating the light.
So, for instance, in fiberlaser systems we're after the
(24:16):
high power, and for our heliumsystem we want to make sure that
our laser wavelength not justthe wavelength but the spectrum
of that laser lies within theabsorption band of the helium.
Turns out that in the upperatmosphere that's on the order
of something like a gigahertz.
This is all a temperaturebroadened stuff, but anyway we
(24:38):
want to make sure that our lasersignal is the spectral
bandwidth is much less than theone gigahertz.
Turns out that in opticalfibers this leads to
nonlinearities, in particularstimulated brillo on scattering,
which is an interaction betweenthe light wave and an acoustic
wave within the fiber.
That can greatly limit theamount of power that you get out
of it.
So it's not so much that youwant to get the power out of it,
(25:01):
but you have to then devise anoptical fiber that can also
support that kind of powerlevels while somehow
circumventing the effects ofbrillo on scattering.
There are several ways to do it.
It might be beyond the scope oftoday's discussion, and then on
top of that, of course, are allthe optics, and so normally
(25:24):
when we send a beam out, ifwe're going over long distances
it's different of over shortdistances, but maybe we don't
want the divergence to be toolarge, because as we come up
through the atmosphere we don'twant to have our beam expanding
to many hundreds of kilometersin the far field, and so what
we'll do is to reduce thedivergence.
We'll do a beam expansion andof course all of the optical
(25:47):
components that go into thatexpansion then have to tolerate
that kind of power.
So there are a lot of differentthings that we think about.
And then ultimately, as we'rerunning, we think about device
longevity.
Are there components to thatsystem that might fail over time
, especially when you're doingsomething like a remote
(26:07):
measurement, or you're sending alaser system onto an autonomous
vehicle or even a rocket,because I wouldn't call that
necessary.
It's autonomous, I guess, in away, but if you're just
launching and it's doing itsthing, you want the system to
succeed and not fail during itsflight.
And then, on top of that too,of course, when you're on a
(26:29):
platform such as that one, youthink about vibrations, things
shaking.
What's interesting about thatsystem is it's not so much
making the measurement once weget to the layer that we're
interested in the sodium layer,it's the ride that it takes
getting up there, and so whenthings are shaking, it has to
survive the ride.
Once it gets to the layer,everything's nice and smooth,
(26:49):
all the rocket engines shut offand it's not a big deal.
But then we also think aboutmaking sure that the wavelength
itself is stable enough again tobe held within the absorption
band of interest.
There are temperaturefluctuations, vibrations and
things that are happening.
There's a possibility of thewavelength walking off For
(27:10):
systems with motion, such as therocket.
Now we also have to contendwith a Doppler shift.
So the fact that our rocket ismoving gives us another degree
of complexity, in that we haveto understand not just the
wavelength, but how does theobservation change, given the
fact that the rocket itself ison a moving platform?
Speaker 2 (27:30):
Wow yeah, there are so many layers of complexity
that you just went through that.
I want to peel away a littlebit and ask you a little bit
more detail.
The stimulated balloonscattering is an incredibly
fascinating phenomenon and Ijust want to clarify with you.
(27:56):
It is the.
Where does the acoustic wavearise from?
In the fiber.
So let's start there.
I have so many questions aboutwhat you just explained.
Speaker 4 (28:07):
Oh sure, sure.
Well, I guess the easiest wayto think about it, the simplest
model, is to consider the fiberitself as being at temperature,
it's just room temperature.
Whatever it is, there arevibrations that are present in
the material, and so you couldthink of sort of the glass
itself as being kind of a bathof acoustic waves that are all
(28:32):
present.
And as the light wave passesthrough the optical fiber, there
will be bragg mesh with some ofthose acoustic waves, as your
bragg.
The acoustic wave itself, ofcourse, is a longitudinal
pressure wave, and if you havepressure in the material, that
changes the refractive index,and so the grading itself looks
a lot like a fiber bragg rating.
(28:52):
And so your optical wave, whenit comes in, will be bragg
meshed with some of thoseacoustic waves.
Again, one in principle.
But the optical fiber can be anacoustic wave guide and it can
actually interact with multipleacoustic waves and so on and so
forth.
But to keep it simple, thelight wave will then, will
(29:12):
scatter from that bragg-matchedwave.
The scattered light wave willthen well, it's also Doppler
shifted, by the way, because thesound wave is moving at the
speed of sound.
So you have a frequency shiftassociated with that reflected
wave.
That scattered wave then willinterfere with the original
forward-going wave.
That interference pattern thenfeeds that original acoustic
(29:33):
wave, because now the originalacoustic wave becomes amplified,
its reflection becomes stronger, and so you can kind of see
this positive feedback cyclesort of forming.
Eventually you reach some powerthreshold known as the threshold
power, I guess where yourstimulated process takes over
from noise and instead ofgetting light out of the fiber,
(29:57):
much of it gets reflected backtowards the center.
So it's a problem that you seenot only in lasers but also in
telecommunications.
In telecom the easiest way toavoid this problem is to broaden
the spectrum, as Brillouinscattering is a coherent process
that requires a line widththat's less than the Brillouin
line width, which is usually onthe order of tens of megahertz.
(30:19):
For us, for the LiDARapplication.
Oftentimes we're not allowed todo that, because we're trying
to make sure that our lasersignal lies within the
absorption bandwidth of thespecies we're trying to measure.
Speaker 2 (30:33):
I see, wow, very cool .
The second topic I wasinterested in was the.
You know, it's prettyincredible that you're working
with these huge powers and I'mcurious if you can comment on
how, practically speaking how,these experiments are done in a
university lab.
I'm sure there are someinteresting challenges there.
Speaker 4 (30:58):
Yeah Well, safety is an utmost concern, so making
sure that the students are awareof their goggles and all that
stuff.
Actually, if I could take aside note before we move on, yes
, of course.
We actually have partners thatdo that.
We partner with Air Force andother groups that do kind of the
(31:24):
high power building for us, andso we don't.
One of the things that I try todo make sure that you know it's
a lot to ask a student to becomfortable about, you know,
working with kilowatts, yeah, socertainly underscores the
importance of collaboration.
Yeah, so this was.
This is a side, that was a sidecomment, not meant for
(31:45):
publishing, just just if that's.
Speaker 2 (31:49):
I guess the editors would Sorry, I couldn't find the
mute button.
Yep, that's fine, peter, okay,okay, yeah.
Speaker 1 (31:54):
I also just wanted to take this opportunity to say
that it's going really good.
The podcast is so interesting,so I'm really excited about this
.
Okay, yeah, I don't know ifwe're going off topic by talking
about the FIWAR technology ornot?
Speaker 4 (32:10):
No, you guys.
Speaker 1 (32:10):
I mean, like I said, it's a conversation in lead back
and it's really interesting Meand Karen are just saying how
we're both learning so much, soyou're doing great, but I'll
just make sure.
So you just want to remove fromwhere you said to the side note
right, yeah, yeah, yeah, yeah.
Speaker 4 (32:25):
No, I mean like I said, we We'll go up to 100
watts, a couple of 100 watts,but that's sort of where I like
to draw a line, because beyondthat point there's a real risk
for the students and unless theyhave a lot of experience
working with these things, it'sbetter if someone else is
willing to do it for us.
Yeah, here you go.
Speaker 1 (32:45):
Yeah, yeah no, that makes complete sense.
Okay thank you so much.
I took no, okay.
Okay, I'm going to go back onme.
Speaker 2 (32:55):
The other question I had was relevant to the rocket
launching, so can you talk alittle bit more about the
challenges involved in designinga laser to be launched on a
rocket Sounds incredible.
Yeah, well, we have.
Speaker 4 (33:12):
The R LiDAR system is comprised of many parts, as
we've already talked about.
You know there's the.
I guess the rocket is fairlylong and thin and when it flies
it has to fly in a way that'sstable and, I guess, predictable
.
But there are multiplecomponents that we have to worry
(33:32):
about.
So one, there is a telescopethat's on board, you know, a
curved mirror that's on boardthe rocket, and so you know when
the Actually the way it'sdesigned is as the rocket goes
up through the atmosphere, youknow different.
You know the fuel pods orwhatever will fall off the back
end.
I'm not an expert in the rocketitself, by the way, but
(33:56):
thinking about you know kind ofruggedization.
So one, you have to make surethat that telescope or that
mirror survives that process.
So actually figuring out how toepoxy it to a stable sort of
substrate such that it doesn'tcrack or shift or move out of
place, that's really important.
(34:17):
Of course the.
You know we have our mirror andthat's in a different place
from the laser.
The laser itself is on ahardened breadboard.
All the components are in, youknow machined grooves, kind of
where everything sits, you knowmechanically ruggedized and of
course, locked into place withvarious epoxies and then the
(34:41):
output of that system, of course.
Well, I should go back andcomment.
One of the things about thissetup and you know when one is
thinking about making sure thatthe laser itself stays aligned
during that flight is to usecomponents that are a little bit
bigger than you would usuallyuse in a lab.
You know it's kind of in.
(35:02):
You know it's like a typical,you know, university laboratory
or something like this teachinglab or research lab or whatnot.
So what you want to make sureis we have things like lenses
and mirrors that directdifferent parts of the beam to
different locations inside thelaser itself If something shifts
.
You know, like the crystal, forexample, the Raman crystal is
(35:25):
large enough such that ifthere's a shift in the position
it doesn't matter because thecrystal is large enough to
tolerate that change in position.
So that's part of a key to that.
The other part of it, of course, is making sure that things
stay put.
You know you want to make surethat everything is locked into
place.
(35:46):
We actually I'm not a mechanicalengineering expert, but this is
a testament to the multi, youknow, kind of multifaceted
nature of doing research likethis is.
We have people from themechanical engineering
department helping us to designthat stuff.
You know, it's very, like Isaid, very multidisciplinary.
It's like, you know, how do we?
I understand photons and Iunderstand how to generate them,
(36:09):
but how then do we drugadizethis thing?
Okay, and so that's part of the, you know, yeah, yeah, part of
the whole story.
And then, of course, as ourlaser is in a different position
from the mirror, you know we'lltake an.
You know, for example, ourconcept is to bring an optical
(36:29):
fiber, you know, to the outputof the laser, and then the
optical fiber will bring thebeam over to the telescope and
then our beam will, you knowkind of couple to the telescope,
be reflected from the mirrorand outwards in a truly
monostatic configuration.
And then that same telescope isused for receiving Another
(36:52):
optical fiber on the receiverend of course, collects that
light and then takes that to yetanother part of the rocket that
has our photodetectors, whichare actually photomultiplier
tubes, and making sure that thatstays aligned is also
imperative.
So it's, you know, there'sfibers, there's the mirror,
there's the laser, and it's thealignment of the various things,
(37:13):
plus the rigidity, thestructural integrity to make
sure that things don't breakapart, shake apart or become
misaligned.
So there's a lot to think about.
It's not a trivial task, it'sjust, yeah, a lot of things to
think about.
Speaker 2 (37:29):
That's quite an understatement.
It's very exciting and I assumethis is one of the reasons what
makes you so passionate aboutthis research, because it's
always something new to learnand problems to solve.
I'm curious just once therocket actually reaches the
(37:53):
layer that you're interested in,does it simply float?
Like are you still controllingthe motors?
Like how does it actually work?
Speaker 4 (38:04):
It's going to.
Basically it's going to ride upto roughly 130 kilometers, you
know, through its fuel that'sgoing to be on board and once
that's spent the rocket will nolonger be.
You know, it won't be propelled,it's going to undergo a
controlled fall and the way thatwe have it set up is it's
(38:28):
actually going to be spinning asit's falling.
Of course, those are the rocketscientists that figured that
out.
Again, there's a whole team ofpeople involved in this
development.
But as it's coming down it'sgoing to kind of rotate and so
what we're going to do is we'regoing to get a kind of a 360
degree field of view of thereturns or the turbulence field
(38:52):
that's in the vicinity of therocket.
Again, this isn't turbulencecaused by the rocket, it's, in
principle, turbulence-relatedatmospheric dynamics and that
fall process is actually quitesmooth.
Actually, the way they describeit is like a turbulence-free
kind of floating.
That happens, and you know wecan only measure, you know,
(39:15):
through the sodium layer whichends at about, you know, 80 to
85 kilometers or so, and thenthe rocket itself will land in
the ocean, near the shore, andwill retrieve it to hopefully
it'll survive, of course, thatprocess, the impact, so that we
can use it again.
Speaker 2 (39:34):
That's incredible You'll get your laser back.
Speaker 4 (39:37):
Well, that's the hope .
That's the hope you never know.
Speaker 2 (39:44):
So let me ask you about the another challenge that
many of the listeners areprobably aware of is, since we
are in the in LiDAR, since weare trying to measure such a
weak signal, can you talk alittle bit about the detection
challenges on the detector side?
Speaker 4 (40:02):
Certainly.
But again, you know, whenyou're designing a LiDAR system
you kind of have to have apriori sort of a sense of the
signal that you expect to getback, and that will help to
guide your choice of receiver ordetector.
The first order, of course youknow you have a wavelength that
(40:23):
you're producing and then someother wavelengths.
Maybe the same wavelength or adifferent wavelength will come
back, and you want to make surethat your receiver, of course,
spectrally overlaps with whatyou're trying to detect.
So you know, for instance, youknow if you're trying to look
for a 1300 nanometer signal witha silicon detector, that's not
going to work so good.
So of course that's the firstpriority.
(40:43):
The second is to understand howmuch power or how many photons
you expect to get back.
If you're expecting a largesignal to come back, oftentimes
if you're close range to anobject and it's, you know,
perhaps an automotive LiDAR youmight get a lot of signal back,
and so you can use a standarddetector for something like this
(41:04):
, whereas if you are expectingto get just a few photons back,
then we have to move to a photoncounting device.
So those could bephotomultiplier tubes.
Photomultiplier tubes work onthe photoelectric effect.
Basically, you have thismaterial, you know a photon
comes in, the energy is abovethe work function, it spits out
(41:26):
an electron and then that'samplified through a chain of
what are called dinodes and youknow you get, you know, maybe a
factor of a millionamplification.
In that case, just like withanything else, the higher the
work function, the lower thenoise that you have.
Same as with semiconductors.
You can also think about photoncounting semiconductors.
(41:47):
However, the smaller the bandgap, the more noisy they become,
as thermally generatedelectrons can traverse the band
gap.
And so oftentimes, when we'redealing with longer wavelengths,
you know where, like, the workfunction is low or the band gap
might be low, then we have tothink about actively cooling the
device.
Yeah, fortunately for us withthe sodium those wavelengths are
(42:13):
long enough, or sorry, theenergies are high enough.
The wavelengths are shortenough that we can get away with
an uncooled receiver system,whereas once somebody moves,
once you move to like 1083nanometers, where there could be
a lot of background, lightbackground and then thermal
noise, of course, in thereceiver system, then we might
have to think about cooling thedevice.
Speaker 2 (42:35):
So actually there's a question for you, Kristen how
are we doing on time?
I just realized we've gonequite a bit long, Do I?
Speaker 1 (42:43):
kind of have to wrap up yeah, go ahead.
Yeah, we have 10 minutes left.
We don't have to like stick tothe 10 minutes, but I definitely
recommend not going that muchover.
It may be just if you want topick out something that you
really wanted to make sure getsincluded, but I would try to
keep it within like 15 minutesif possible.
Speaker 4 (43:02):
Well, do you guys want to?
I've got this text written outfor, like, what are other types
of light ours?
Could that be like a goodclosing thing, or?
I mean, I wrote that outPerfect.
Speaker 2 (43:11):
Yeah, I don't know Right there yeah.
Speaker 4 (43:17):
This way I could just read it and then you know we
could.
That way, we would bring thelast 10 minutes.
Speaker 2 (43:26):
So don't we need to talk about Akhil's questions, or
no?
Speaker 1 (43:31):
Maybe like it's just Peter's 10 minutes, Sorry yeah
yeah, yeah.
Speaker 3 (43:37):
So if Peter and Rajesh could actually finish in
the next 10 minutes, then I'vegot a couple of questions and
I'll try and combine some of thequestions.
So I asked the important onesand overall we'll still stay
within the time period.
Speaker 2 (43:50):
So first let's move on to Dr Kamala, Is that okay,
Peter?
Speaker 4 (43:54):
That sounds great.
Rajesh, do you have it open?
Speaker 2 (43:58):
Yeah, I have it open, oh, okay.
Speaker 4 (44:01):
Yeah, so I was thinking maybe this kind of this
what are other types of lidars?
Just to kind of talk aboutother you know, Okay, cool.
Speaker 2 (44:10):
Okay, three, two, one .
So, Peter, so far you've givenus a fantastic description of
the challenges involved in yourspecific research.
I'm curious what are the typesof lidars exist?
And also if you can also talk alittle bit about opportunities
and where this field is going tocreate.
Speaker 4 (44:31):
Sure, that'd be wonderful.
Thanks for the opportunity.
So other types of lidars well,we've already discussed the
residence fluorescent systems.
Others are based on either theelastic or any elastic
scattering of light from theatmospheric constituents.
In the case of elasticscattering, these are based on
(44:51):
scattering from molecules oraerosols.
Usually we think about Rayleighor Me scattering in that case.
For example, upper atmospheric,such as exo or mesospheric
Rayleigh lidars are most oftenused to track dynamics in those
regions of the atmosphere.
For example, one such dynamicprocess involves gravity waves.
These are distinct, of course,from gravitational waves.
(45:11):
They relate to the motion ofthe atmosphere up and down
vertically with time.
Importantly, tracking eventssuch as these things again also
helps us understand how energycouples between the regions of
our atmosphere and enablesglobal energy transport models.
Aerosol lidars can, for example, be also used for tracking air
quality near the ground.
(45:32):
So pollution sensing and thatkind of thing.
Lidars that make use of Rayleighor Me scattering also include
something that Lidars known asdifferential absorption Lidars.
There what you do basically isyou have your laser beam again
it's pulsed, most often times todo ranging, and then you tune
your laser beams on anabsorption feature and off an
(45:53):
absorption feature, if you knowwhat the absorption
cross-section is for thatfeature.
The ratio of those two signalsgives you a relative abundance
of that constituent.
These types of Lidars can beused to measure greenhouse gases
again, such as water vapor, asI had worked on in the past, and
carbon dioxide, for instance,as well.
These two atmosphericconstituents, among others, of
(46:16):
course, can be measured in thenear infrared.
That means that we can use lessexpensive and possibly less
noisy sensors and less expensivelasers, for instance.
Other gas sensors, such asthose that look for nitrogen or
sulfur oxides, require lasers inthe mid-infrared, which is more
challenging from severalperspectives.
Different lasers at thosewavelengths produce insufficient
(46:38):
powers, especially if you wantthem to be pulsed Detectors.
Of course, now you're talkingabout low-band gap materials,
they become more noisy receivers.
You also have Doppler systemsthat make use of Rayleigh
scattering, but the receiver isable to measure a change in the
frequency or the Doppler shift.
These systems are oftenactually these days commercially
(46:59):
used to measure wind speed inthe vicinity of wind turbines.
Other LiDAR technologies basedon any elastic scattering are
like Raman and Brillouin lasers.
Like Doppler LiDARs, thesesystems rely on the measurement
of change of frequency of anoutgoing laser signal, of course
after interacting with themeasure end.
For instance, we talked aboutBrillouin scattering.
Brillouin scattering is aninteraction between a light wave
(47:22):
and an acoustic wave,oftentimes ultrasonic or
hypersonic.
The light scattered byBrillouin scattering, just like
it is an optical fiber, isfrequently shifted, and this
frequency shift can be a verystrong function of environmental
things like temperature.
Just as a result of this, forexample, brillouin scattering
based LiDARs have foundapplications in ocean
(47:43):
thermometry, which becomes avery important thing to measure
Again global circulation models,not in the upper atmosphere but
in our oceans.
Lidars can also operate in boththe time and frequency domain.
We talked about pulse LiDARs,but the time domain systems are
pulsed Again.
These are time of flightsystems.
Frequency domain LiDARs, on theother hand, use frequency
(48:04):
modulated continuous laser,where the laser wavelength is
swept in time.
There part of the output beamis taken as a reference or a
local oscillator.
Then think about like you senda signal out.
If our frequency is constantlyscanning or sweeping, then the
time delay between what comesback and the local oscillator
(48:25):
will give rise to a frequencyoffset between those two things.
Then, of course, if we beatthem together and measure the
frequency shift, that gives usthe time delay or equivalent of
the distance.
Lots of different ways to dothis.
As far as opportunities andbottlenecks and things go.
Challenges again, there are alot of challenges in the
(48:48):
development of LiDARs.
This is related to the laserwavelength and power.
Going back to the automotiveLiDAR application, ice safety
becomes a concern.
Ice safety is a verysignificant, a very serious
limitation to the feasibility ofLiDAR systems.
Again, we want large telescope.
(49:08):
Necessarily.
We want high power.
You can't think about reallyputting power out that might
damage someone's eye.
You also can't imagine puttingone meter telescope on top of a
car.
That's one way to think aboutlimitation.
Again, low noise, highefficiency receivers can be a
(49:29):
challenge.
We talked about silicondetectors that have been
developed for many years, a verymature technology.
Dynamic range available fromthem is also very large.
You can do photon counting withsilicon all the way up to high
power measurements.
But if a desired operatingwavelength lies outside that
spectral response of silicon,different materials have to be
(49:50):
used.
Again, some of these thingsaren't then amenable to photon
counting.
We have to think aboutdifferent ways to detect these
signals, such as a modern pushtowards things like far infrared
, superconducting, single photonreceivers.
Anyway, a lot of opportunitiesin new lasers, new receivers,
(50:13):
autonomous operation, of course,power, more efficient solutions
are important.
We think about all those thingsas well.
Again, as we talked about theenvironment and the platform on
which the laser is placed or theLiDAR is put, it's going to be
a serious limitation.
Speaker 2 (50:29):
Wonderful.
Thank you, pete, so much forspending the time going through
lots of the details about notonly your project but also an
overview of the opportunitiesand all the excitement around
LiDAR technology.
I have certainly learned a lotand enjoyed this conversation
(50:49):
very much.
Now I'd like to pass the batonto Akhil for the remainder of
the podcast.
Speaker 3 (50:57):
Thank you very much Rajesh, thank you very much
Peter.
That was absolutely incredible.
The amount of things that we'veactually had a conversation
about and so much of what we canunpack through the course of
the podcast and afterwards isincredible, and I thank you both
very, very much for that.
I've got a couple of questionsbefore we close for today, and
(51:19):
the first question I'd like tokeep for a minute Peter, both
interested.
Now, obviously, as I havelearned, being a PhD student and
an early career researcher anda postdoc, the first thing you
do when you start talking tosomebody is you Google them and
you find out what they actuallydo.
Now, interestingly, with mybackground in biophotonics,
(51:39):
everything that Peter does interms of time of flight imaging,
in terms of time of flightsensing, lidar systems, low
light conditions for LiDARsystems specifically, all the
scattering methods, everythingare also seen in Rajesh's
research of brain imaging.
Do you ever see the crossoveracross the fields?
(51:59):
Do you think something in LiDARsystems would be interesting to
Rajesh and do you thinksomething in biomedical optics
would be interesting to Peter?
A question to the most of you.
Speaker 2 (52:12):
Peter, you want to.
Speaker 4 (52:17):
That's a very interesting question because
although the different fieldsuse different names, different
words for technologies andmethods, a lot of the approaches
are all identical FMCW, forinstance, LiDARs, which you find
at automotive, LiDARs,automotive, autonomous vehicle
(52:41):
sort of things.
The same technology can befound in precision metrology on
the micro scale, so that couldalso include bio applications
and bio imaging things.
Speaker 3 (52:59):
Because it's quite interesting, when Peter was
talking about everything he wasmentioning, he was talking about
fluorescence, about LiDAR,about valence scattering, all of
which I'm sure Rajesh andmyself have seen in tissue
imaging.
So, rajesh, you were about tosay something.
Speaker 2 (53:18):
Peter's exactly right .
I think there's a significantamount of cross talk and it's
one of the reasons I try toactually talk to folks outside
of my discipline is that you notonly recognize areas that are
common but new ways of solvingvery similar problems.
(53:38):
So in dealing with scattering,certainly in macro scale imaging
, people have applied TemuFlightfor imaging through scattering
media in the microscopycommunity because the dimensions
are so small that the timedifference of the reflector
pulses are way too small, atleast as far as I'm aware of.
(54:01):
I think it's quite challenging,but I wouldn't say never, but
it is a little more challengingthan doing it for much larger
distances, I would say.
But it feels like adaptiveoptics clearly have been applied
in both areas.
Biophotonic adaptive optics ispretty standard nowadays, but it
(54:25):
was adopted originally fromastronomy and I have completely
different fields.
Speaker 3 (54:35):
Absolutely.
I mean there is obviously.
There's a big difference,literally, between a mirror used
in the telescope and a mirrorused on a digital micrometer
device, but we're stilleffectively still using a mirror
.
Speaker 2 (54:47):
Right, right yeah.
So, it really underscores the Ithink it's an important point
that you're raising.
It underscores the importanceof understanding the
fundamentals of whatever it isthat you're learning, because as
an engineer or scientist, it'smuch easier to translate your
(55:10):
skills to very different fields.
I think it's an important pointto convey to the young
engineers and scientists who arelistening to this.
Speaker 3 (55:19):
Absolutely.
My next question again to theboth of you is, as quickly as
you can and as easily as you can, what are the two things, one
for a academic sphere and onefor a personal?
Or?
Here's a good advice to be agood researcher.
Kind of advice would you giveto somebody listening to this?
(55:41):
Where should the next LiDARsystems engineer focus on?
Also, what should every youngresearcher try to do right now?
And maybe, Peter, would youlike to go first?
Speaker 4 (56:00):
Ah, boy okay.
Speaker 2 (56:07):
I can go first if you want, I mean.
Speaker 4 (56:10):
Please, maybe you'll give me some ideas.
Speaker 3 (56:13):
It's just a question of all of us being very polite
with each other.
So, Radis, how about you gofirst?
Speaker 4 (56:20):
Well, we can edit these things out, right.
Speaker 2 (56:22):
Yeah, exactly, I'd say as a new I don't want to use
the word young, because you maynot be young in mind, young in
a field, person entering a field.
I think it's really importantto really talk to as many people
as possible to understand thelandscape and understand the
(56:43):
challenges often which are notnecessarily obvious or even
written down somewhere.
So it's really useful tounderstand the culture and the
challenges of a field as much aspossible, and the way I think
it's an effective way tounderstand it is, of course,
talk to your peers, talk to yourmentors, talk to your competing
(57:07):
labs, if there are any, go toconferences.
Really try to talk to as manypeople as possible, even if
they're not directly related toyour field.
You learn a lot.
This means my personalexperience.
Speaker 4 (57:25):
Yeah, I can actually follow up on that.
I agree entirely with thatremark, Rajesh.
You did your undergrad at MIT.
Speaker 2 (57:40):
My graduate work, but go ahead.
Speaker 4 (57:42):
Sorry, your graduate work?
Yeah, we can start over.
I fully agree with the commentsthat you made.
Those are very important points.
I fully support them.
I guess you did your graduatedegree at MIT.
Do you have familiarity withOlin College's user-oriented
collaborative design course?
Speaker 2 (58:04):
Unfortunately not, sorry, please go ahead.
Speaker 4 (58:09):
I actually had the privilege of teaching that as a
transplant here at the U of Ifor a few semesters.
It was taught within the Artand Design program, and Olin
College actually teaches that asa very first semester freshman
course to kind of help studentsunderstand how to go out and
find problems.
It's not so much finding asolution to a problem, but it's
(58:31):
going out and understanding howto find where the problems exist
.
What's a problem?
A problem is something thatcould make someone's life better
.
A problem could be somethingthat helps us understand our
environment better, Anywherewhere you feel like you might be
able to make a positive changefor humanity.
And unless you're able tounderstand how to go out and
(58:52):
find those problems, it's hardto understand whether the
solutions that you're generatinghave any value or have any
meaning.
And so I agree the whole idea.
That course that I was involvedwith actually got the students
up out of the classroom into thefield talking to people.
Hey, what do you think isimportant?
What could make your lifebetter From the perspective of a
(59:15):
LiDAR system?
What is it that we need tounderstand to really get a grasp
on the meaning of globalwarming?
For instance, Do we have tomeasure carbon dioxide?
Or is there an atmosphericmodel somewhere where there's a
scientist who's not a laserperson who says, hey, if we had
this information, this would betransformative, and so the
(59:37):
student then can go out findthat problem and then speak
targeted solutions to solvingthat problem?
Speaker 3 (59:45):
I think that's a very interesting perspective and
interesting advice as well,because somebody I look up to
quite a lot, in addition toeverything that you've mentioned
, has also quite vocally saidthat sometimes the people that
you actually work with arealmost as valuable, if not more,
than the actual problem thatyou're trying to solve, and such
(01:00:06):
is the nature of academia, suchis the nature of industry, such
is the nature of everythingthat we do today, that the
people that we work with add somuch more value.
So, going back to Rajesh'sadvice of speaking to more
people, building thoseconnections, and combining that
with Peter's idea of the here'sa problem I would really really
like to solve makes up for sucha perfect motivational statement
(01:00:29):
.
For instance, where anyonetaking on a project, a research
problem, across any field,really and I think if you'd
actually seen me on video whilewe were having this conversation
, listening to the both of you,I was simply going yep, they've
answered that.
Yep, they've answered that.
Yep, they've answered that.
So you've left me with almostno questions to ask, which is
really really good.
(01:00:53):
I'm going to end today bythanking you both for your time.
It's been a wonderfulconversation.
We have heard about LiDARsystems, about how margin
atmospheres can be measured andmonitored, the value of it for
astronomy, looking atfluorescence, looking at low
light problems.
We touched a little bit onbrain imaging, although that's
(01:01:17):
tangentially related.
However, as in research,everything is connected.
I think one of the biggesttakeaways for me was how
multidisciplinary andinterdisciplinary research today
and problems today have become.
There's electronics, there'soptics, there's rocket science,
and I never actually, and neverbefore today, have I realized
(01:01:39):
how much someone like Peterwould really like his laser back
after it's gone to space andcome back.
So I think that's quite nice Ajourney of a laser that's
probably traveled more than me.
Speaker 2 (01:01:54):
I do have one last question for you, Akhil.
Speaker 4 (01:01:57):
Yeah, go ahead.
Speaker 2 (01:01:59):
Before we end, what are some key takeaways that we,
as more advanced in the careers,should know how we can support
early stage researchers likeyourself and your peers.
Speaker 3 (01:02:18):
Okay, so how much time do you have?
How could I list, so, I think,the conversations that people
can have?
There is an innate fear, whenit comes to every early career
researcher and PhD student, towalk up to an established
academic at a conference and gohere's a question I have.
(01:02:41):
I read a paper that youpublished and I think I have a
few questions.
Would you have an opportunityfor a conversation?
I think the, as in mostacademics and most sorry, I
correct myself most early careerresearchers are looking for a
(01:03:01):
mentor, somebody who can eitherbe a mentor for a long duration,
somebody who's going to who'sat the other end of their career
to turn and say I will guideyou through this procedure, or
somebody who can answer thequestion as best as they can in
that moment, effectively helpingthem along their journey.
I think the best contributionsI have had from established
(01:03:26):
academics, from their careers tomine, was simply time, just the
opportunity to talk to somebodymuch further along in the
journey and for them toeffectively tell me I did this,
don't do this or I did this.
I think you should also do this.
I think there's no bettersupport than a good mentor, some
(01:03:48):
good advice and a generoussupport of nature really, so
does that answer your question?
I've got a bigger list, though.
Excellent.
Speaker 2 (01:03:56):
Excellent.
No, that's a fantastic place.
I've got a bigger list thatsays sorry, go ahead.
Speaker 3 (01:04:05):
No, no, no, go ahead.
I've got a bigger list that'sgot cameras, lasers, optic
systems.
I'm going to put Peter Linersystems on it.
It's a shopping bag.
Speaker 1 (01:04:17):
That was so, so good.
I think that might don't tellthe other participants, but
that's like my favorite episodeso far.
So thank you so much, I think.
Karen Karen did you want to aska question?
Speaker 2 (01:04:27):
It was my first and I'm hooked already.
Speaker 3 (01:04:31):
I found myself taking notes and, like I don't have a
clue, but this is so interestingI have to write something down.
Speaker 2 (01:04:36):
but, pete, you had said when they said what got you
into this, you said it wassomething you did in your
undergraduate group work or astudy group and that took you
back there.
Speaker 3 (01:04:48):
Can I ask whose?
Speaker 2 (01:04:48):
group that was.
Speaker 4 (01:04:50):
George Papin, okay.
Speaker 2 (01:04:53):
I said to Kirsten, I said it has to be one of our
guys, because at one point ourentire bog was almost from, you
know, Urbana Champaign.
Oh yeah, we have to know who itwas.
Speaker 4 (01:05:07):
I don't know if George was ever on the bog, but
we've got.
I mean, ken Chiquette is in theoffice next to mine.
Speaker 2 (01:05:14):
He was president at some point, yeah.
Speaker 4 (01:05:18):
I know George from other things, but like we, I
mean you know we oh yeah.
Yeah, jim, and yeah, it'sinteresting, because you know
what one regret that I have isthat George's advisor was Bahasa
.
Okay, I've actually never methim.
Speaker 1 (01:05:37):
Oh man.
Speaker 4 (01:05:39):
My grand advisor, or whatever you call it.
Speaker 1 (01:05:46):
Is it Gary Eden?
There too?
Speaker 4 (01:05:48):
Hey, gary is here.
Yeah, he's retired recently.
He's spending more of his timein Texas these days, kind of in
retirement, but yeah, yeah,gary's here and.
Speaker 2 (01:05:56):
You know that's such a thing.
Does everybody from Illinoiseventually head to Texas?
Because there's?
Speaker 1 (01:06:01):
a couple of them I know Shu Ling.
Speaker 2 (01:06:04):
Everybody went to Texas, Yep.
Speaker 4 (01:06:05):
Yep, yep.
So yeah, I don't know what'sgoing on.
Speaker 2 (01:06:12):
I guess you know they've got their oil field
endowments, I guess they're onpump.
Speaker 1 (01:06:18):
Yeah, that's hysterical.
Um, okay, all right, so we're15 minutes over, so I know how
you guys gave so much air freetime, so I'm going to wrap it up
so you guys can get some timeback.
But I just want to justseriously tell you guys how
grateful and how much weappreciate you participating in
this, and we probably will askfor you guys to come back as a
(01:06:39):
moderator or guest speaker.
So just keep your eye open andI'll let you guys know as soon
as the episode is you know hasbeen edited by our editor, and
then I'll let you guys know assoon as it's up on Spotify as
well.
Excellent.
Speaker 3 (01:06:56):
Thank you, thank you very much, thank you.
Speaker 4 (01:06:59):
Thanks everybody.
Yeah, Okay, if they need to,you know to dub over anything,
because maybe my you know, SouthSide of Chicago accent was made
things unclear.
Speaker 1 (01:07:15):
But in that case I'll definitely reach out to you
guys.
But our editor's pretty goodand you guys really did like
such a good job.
You're all naturals.
Speaker 4 (01:07:23):
Thank you very much.
Speaker 1 (01:07:24):
Thanks everybody, thank you, bye, bye, bye, bye.
Speaker 2 (01:07:28):
Bye.
are finalized, but we'll send you the episode as
soon as it's edited, just so youcan review it and kind of give
it the final approval.
I don't imagine you guys aresaying anything.
We shouldn't, but just in caseyou wanted to listen really
quickly and spot-track it, oryou listen to it.
Speaker 2 (00:19):
You mean you'll give us the veto power if we say
something controversial.
Speaker 1 (00:27):
Yeah, we actually can .
We want you guys to be proud.
Like you said, you wanted toput it on your social media.
We definitely want youencourage you to be proud of the
episode and our editor isreally good.
So if we want to changeanything, we can.
The only thing we can't changeis the intro song, which is very
fun.
You guys will hear that.
But, yeah, we can edit anythingthat happens in the episode
(00:50):
which goes into what I'm goingto say next.
This is really relaxed.
If you start to answer aquestion or start to ask a
question and you feel like youkind of misspoke or didn't say
it how you wanted it to come out, feel free to say I'm just
going to do that again and we'lledit it out.
We're not on live TV, nothinglike that.
(01:12):
So this is really relaxed andthe editor has a really good eye
to fix anything if somethingdoesn't flow right.
So if there's no otherquestions, I will pass it off to
a kill the host to kick it off,and, feel free, I'll be on with
you guys the whole time.
So if I hear something that Imight say, oh, let's redo that,
(01:34):
I might pop in, but likely not,because we do want it to be
organic, but if you have anyquestions that arise during the
conversation, I'll be here, orany technical questions.
Speaker 3 (01:45):
All right, excellent, peter Rajesh ready.
Speaker 4 (01:50):
Yep sounds pretty good Excellent.
Speaker 3 (01:53):
So in three, two, one .
Hi everyone and welcome totoday's episode of Illuminated.
I am Akhil and, as theAssociate Vice President of the
Young Professionals and theChair of the Young Professional
Advisory Committee, it's mypleasure to be your host today.
I'm a biomedical physicistmyself working at the University
(02:16):
of Glasgow as a leading humanearly career fellow.
In my role for the IxativeEthnic Society, I'm supporting
and promoting initiatives verymuch like this podcast, to raise
the profile of valuable youngprofessionals within various
sectors.
The Young ProfessionalsInitiative is for graduate
students, post-doctoralcandidates and early career
(02:37):
professionals up to 15 yearspost their first degree.
This affinity group within theIxative Ethnic Society is
committed to helping one pursuea career in photonics.
We're here to one help evaluateyour career goals, to better
understand technical pathwaysand subject matters, refine
skills and finally growprofessional networks through
(03:01):
mentorship.
Now onto the more exciting ourpodcast for today.
Today is a particularlyinteresting topic that we're
talking about.
Working in classical andquantum optics myself, and with
a keen interest in time of lightimaging and sensing, our topic
is of a particularly personalinterest to me.
We're discussing LiDAR systems,technologies and current
(03:24):
questions regarding the state ofthe field and the future of the
field itself.
Our very special guest,professor Pete Dragitch, and
moderator Rajesh Menon, are herewith us.
We're going to technology,career journeys, advice from
within and beyond research.
Now, firstly, thank you verymuch for listening to this
(03:45):
episode.
I am already certain it's goingto be a great one, and I hand
over to Rajesh for the nextintroduction.
Speaker 2 (03:56):
Great Well, thank you , O'Kill.
I'm very excited to be herewith both of you.
We are honored to have PeteDragitch as our expert for today
.
Speaker 3 (04:15):
Sorry, I know Kristin's already listening in.
Could I just go back?
Until?
When I actually finished aboutthank you for listening to this
episode, I realized if I justscroll the page, I'm doing the
introduction for Rajesh as well.
I'm going to do theintroduction for Rajesh and then
I'll hand over to Rajesh again.
Speaker 1 (04:34):
Okay, perfect, good catch.
Speaker 3 (04:36):
Yeah, I mean literally scroll.
Speaker 1 (04:41):
Okay, go ahead, you can just pick up from there.
Speaker 3 (04:43):
Yeah, I'll hand over to Rajesh again in a second.
Speaker 1 (04:46):
Okay, perfect.
Speaker 3 (04:49):
All right, three, two , one.
I will now hand over to Rajeshfor the episode and for
conversations with ProfessorDragitch.
Rajesh Menon is an engineer andentrepreneur advancing
knowledge at the intersection ofoptics, nanofabrication and
computation.
He is a professor in electricaland computer engineering at the
(05:12):
University of Utah, a fellow ofOptica, sbie and a senior
member of our very own IEEE.
After receiving his PhD fromMIT, he co-founded and led a
spin-off company forcommercializing maskless
lithography.
His lab in Utah is exploring amultitude of imaging systems
(05:33):
enabled by nanofabrication andcomputational methods, including
miniaturized endomyroscopy fordeep brain imaging, ultra
lightweight optics for airborneimages, computationally enhanced
diffractive spectral images andmany, many more.
Rajesh is also invested in thesuccessful realization of
laboratory innovations byentrepreneurship and his funnel
(05:57):
for companies.
It is a great pleasure now thatI hand over to Rajesh for the
rest of the episode.
Take it away.
Speaker 2 (06:08):
Great.
Thank you very much for thekind introduction, Akhil, and
it's an honor to be in this finecompany and very excited to
talk about a very pertinenttopic, which is LIDAR.
It's the topic of this podcast.
Lidar, of course, stands forlight detection and ranging.
(06:29):
It is a remote sensingtechnology that uses lasers to
measure distances and many morethings about the 3D environment
which we will learn about today.
Most of us have somefamiliarity with automotive
LIDAR.
In automotive LIDAR, laser beamis emitted from a source and we
(06:54):
measure the time it takes forthe beam to bounce back off from
objects in the environment.
This data is then used tocreate a detailed 3D point cloud
of the area being scanned.
What is really exciting now isthe creation of 3D point clouds
(07:16):
such as automobiles, butincluding surveying, mapping,
forests, urban sprawl,archaeology, environmental
monitoring, etc.
It's a very exciting technology, but just getting very wide
usage, which is, of course, thegoal of almost any technology
that comes out of the lab.
(07:37):
Today we are honored to have anexpert in the field of LIDAR,
Professor Peter Dragic, with usto geek out about LIDAR.
Pete received his PhD from theUniversity of Illinois at Urbana
, Champagne in 1999.
After a stint doing startups,he returned to his alma mater,
(07:58):
where he is currently anassociate professor in the
Department of Electrical andComputer Engineering.
His graduate work focused onthe development of fiber
laser-based sources foratmospheric LIDARs, namely for
the sensing of water vapor.
His current research interestsrange widely from optimal
materials to lasers and lasersystems, including LIDAR.
(08:20):
A particular interest are fiberlaser systems, which offer some
advantages over theircounterparts.
However, they also suffer moresignificantly from power
limitations due tononlinearities.
Therefore, much of Pete'sattention has also been focused
on reducing the impact of thesenonlinearities, and optical
fiber systems for applicationssuch as remote sensing.
(08:43):
The first of two current LIDARprojects is an upper-demospheric
slash exospheric LIDAR for thedetection of metastable helium.
The other is the sodium LIDARthat will take a ride on a
sounding rocket through thelower to middle thermosphere.
It is my distinct pleasure toinvite Professor Pete Dragic to
(09:05):
this conversation.
Pete, let us start with anintroductory question about
could you share with us how youchose to get into the field of
LIDAR and what inspired you topursue these topics?
Sure thing, Rajesh.
Speaker 4 (09:20):
Thank you very much for the kind introduction.
I'm also very pleased to behere in the company of some
really wonderful people, somegreat minds.
To answer your question, Iguess this goes back to my
undergraduate days.
During the end of my junioryear I was looking around for a
summer undergraduate researchexperience pretty much of any
kind.
Frankly, I wasn't sure ifgraduate school was for me or
(09:44):
not, but I was fortunate to finda faculty member working on
semiconductor-based LIDARs whowas also looking for
undergraduate researchers.
At the time.
His group was trying to developa system to measure atmospheric
water vapor concentrations.
Water vapor turns out as a verystrong and indeed the most
abundant greenhouse gas.
It helps to trap radiation,keeping thermal energy from
(10:05):
escaping the earth's atmosphere.
Some of us understand that tobe a source of global warming.
Anyway, I spent a summerworking on the laser transmitter
and became passionate aboutlasers and, frankly, I've been
at it ever since.
In fact, I became a graduatestudent in the same group where
I did my undergraduate research.
(10:26):
I also had a NASA fellowshipduring my graduate days from the
Goddard Space Flight Center,helping with a similar system,
actually for the Martianatmosphere.
The goal there was to look forterrestrial vents of water vapor
that could be indicators of thepresence of things like
microbial life.
What's neat about LIDAR andthis is kind of what keeps me
going is, if you like lasers,for every LIDAR that you build,
(10:46):
you get to build a new kind of alaser system, and so I think
that's really really neat andvery exciting.
Speaker 2 (10:57):
Wonderful.
Thank you, pete.
It's quite instructive that youwere inspired by an
undergraduate researchexperience, which really
underscores the importance ofsupporting and mentoring
students, which I think we'llcome back to later in our
conversation, and I'm alsofascinated by your PhD work
(11:23):
about detecting water vapor inthe Martian atmosphere.
Clearly, it would be one of thegreatest discoveries of human
history if we were to detectproof of extraterrestrial life
forms even outside of solarsystem.
This is something I would liketo come back to as we go through
(11:46):
this conversation, but let usbegin with something more down
to earth.
Could you give us an overviewof what your group is currently
working on, the technologiesyou're developing and their
exciting applications that theywill enable?
Speaker 4 (12:03):
Sure thing.
I'll speak to the two lidarsthat we're developing in our
group, both of which are typesof lidars known as resonance
fluorescence lidars.
So the way that they work isone pixel laser beam tunes its
wavelength to an absorptionfeature of a species.
(12:23):
In the case of our systems theyare helium and sodium.
Those end up being actually inthe upper atmosphere.
There's a layer of sodium,roughly 90 to 130 kilometers up,
that resides there due toablation of mainly meteorites as
they come into the earth'satmosphere.
(12:43):
And then helium, in the upperatmosphere ranging from about
300 kilometers to about 900kilometers.
There's a layer of helium, Ofcourse.
What can imagine if theatmosphere stratified?
The lightest element willappear at the top.
And so what we do there?
Basically, the principle behindresonance fluorescence is,
again, we tune our laserwavelength to an absorption line
(13:07):
, like the D2 line of sodium,for instance, at 589 nanometers.
That species will absorb thatphoton and then re-radiate it.
It'll re-radiate it asfluorescence and therefore it
goes in all four pi-stradians,all directions basically, and
we're looking from somewherelike the ground or from
somewhere where we have atelescope, the helium lidar.
(13:28):
The goal is to measure out toroughly 900 kilometers, 1,000
kilometers metastable helium.
So what happens there is thatsolar radiation comes in and
that energetic particles arecreated, collide with the helium
and excite those heliums intoan upper state, Many electron
(13:49):
volts above the ground state.
Once you're up there, there's afeature, an absorption feature
at roughly 1 microns 1083nanometers actually that can be
used to probe the presence ofthat metastable helium in that
part of the atmosphere, and soof course we want to make sure
our laser wavelength is at 1083nanometers.
What's interesting about thisis that's a wavelength that's
(14:11):
achievable through fiber lasertechnologies, among other solid
state methods, and what we'reinterested in doing is creating
a high power source that can goup far enough into the
atmosphere.
Again, it's a resonancefluorescent system.
So then that laser signal willbe absorbed, It'll be
re-radiated to the ground and wesit on the ground with a very,
(14:34):
very large telescope, such as anobservatory telescope or
something like this, and receivesignal back Again.
If we do, if we pulse the laseror we can actually do other
techniques to sort of do rangeresolution, and we can track and
we can watch the helium, thatmetastable helium concentration,
as a function of time anddistance, and that gives us
(14:55):
information about the dynamicsof the atmosphere.
So the helium itself serves asa tracer.
It's not necessarily that wecare to first order about the
helium itself, although thereare interesting things about
that too.
It serves as a tracer to giveus details about the atmospheric
dynamics.
That second system is asodium-based system, Again at
(15:16):
589 nanometers.
That one is not directlyproducible by a fiber, but again
you start with some sources andyou get to a wavelength
somewhere in the infrared andyou do frequency doubling and
there's lots of neat ways toachieve that wavelength.
But anyway, the idea is thereis a layer of sodium roughly 90
to 130 kilometers, and watchinghow that sodium moves through
(15:39):
the atmosphere gives usinformation about atmospheric
dynamics, the motion of energyfrom lower parts of the
atmosphere to the upper parts ofthe atmosphere.
How do they couple?
A lot of that is still notunderstood by humanity, and
understanding the way thatfunctions can give us better
insight into creating globalenergy transport models for our
(16:00):
planet.
The idea there, of course, thesystem itself will take a ride
on a rocket.
What we're looking for inparticular for that system is
kind of a short-range, rangingfrom the rocket, say, a couple
to a few kilometers, and we'relooking for turbulence effects,
mixing effects.
So what happens during mixingevents.
(16:23):
We're simply using the sodium,again as a means to watch that
process.
It's not so much that we carehow much sodium there is.
Again, there are reasons whyyou'd want to know how much
sodium there is.
For instance, there are guidestar applications where
understanding the concentrationis very important, but we're
using that as a tracer toactually watch the motion of the
atmosphere.
Speaker 2 (16:47):
It's very interesting .
I just want to make sure Iunderstand it.
In the case of the resonancefluorescence, you are exciting
the resonance and watching thefluorescence from the ground.
How is the excitation beamscanned across some field of
(17:07):
view?
How does it actually work?
Speaker 4 (17:11):
We can scan the beam.
Most generally, though, wedon't scan the beam.
It's kind of a line of sight.
We look in one direction.
The beam will expand to someextent, of course.
Think about a milliradian beamgoing hundreds of kilometers.
It'll be a relatively largebeam, so we're really
integrating across its area.
Certainly we can think about ascan.
(17:31):
That becomes a little moredifficult as one goes to large
scan angles because the distanceto the measure end is a little
bit increased.
Speaker 2 (17:40):
In that respect, how do you actually get the range
information from where thefluorescence came from?
Speaker 4 (17:52):
For a LiDAR.
You can do this a couple ofdifferent ways.
The most common approach is touse a pulsed LiDAR, which you
alluded to earlier in thediscussion today.
What you do is you send out apulse of light.
You're basically measuringreturns as a function of time.
It's a time of flight thing.
If you get to some point intime where you start measuring
(18:15):
information, you could turn thatinto or start measuring returns
.
You could create a distancedistribution by scaling via the
speed of light.
Understanding there's a roundtrip involved.
One of the caveats there, ofcourse, is if you do a pulse
system, you want to make surethat your pulse goes out in a
way that you don't alias yourreturn signal from the
(18:39):
atmosphere.
That means that if you sendyour pulse out, you want to make
sure your pulse goes out andthen it leaves the line of sight
to make sure that you're notgetting returns from different
parts of the atmosphere, fromdifferent pulses.
Speaker 2 (18:54):
Ah, yes, yes, I see that was actually one of my
questions was would there bepotential for ambiguity if
sodium at different distancesacross the layer starts
fluorescing from the same pulse?
Is that very possible?
Speaker 4 (19:15):
Yes, it's possible, but because the pulse is
propagating at the speed oflight through that range, when
we receive those returns will bea function of time as well.
Speaker 2 (19:29):
So if we send out a pulse.
Speaker 4 (19:31):
Let's say there are two ranges, X1 and X2,.
Well, distance equals rate,times, time via the speed of
light, of course, and so when westart receiving signals from
the first part, from X1, will bea time different from X2, and
that's how we can resolve them.
But if we have multiple laserpulses that exist at the same
time, then it becomes ambiguousto you know which pulse
(19:54):
contributed from which layer.
Speaker 2 (19:56):
Yeah, yeah, yeah, yeah.
Very cool, and I would assumethat the signal that you receive
back is quite weak.
Can you comment on that?
Like, how much?
What's the efficiency from theexcitation to the received
signal?
And if that is a challenge, howdo you deal with it?
Speaker 4 (20:18):
Yes, that is a challenge actually.
You know you send out a signal.
That might be, you know, forour helium LiDAR we're actually
envisioning kilowatt lasers.
You know the return is going tobe many, many, many orders of
magnitude below what you put out.
Oftentimes it requires photoncounting and so you'll actually
have a receiver or a detectorlike a photomultiplier tube or
(20:40):
an avalanche photodiode orsomething that's configured to
count photons.
Of course that depends on thenumber of returns.
You know, if you have a largeramount of returns, you want to
make sure that your photoncounter can keep up with the
number of photons that arecoming back.
If your returns are very smallor very low the number of
photons, then we have toconsider, of course, ultimately
(21:04):
scaling the receiver design.
So you know, if our returns arelow, you know a couple of
photons such that they'reswamped out by the noise that we
might get, you know, say,thermal noise or background
light from some other source,then we think about scaling the
telescope, you know.
So it's kind of like the trickin LiDAR is power and aperture.
(21:25):
So the more power you have, ofcourse, the more returns you're
going to get, the more apertureyou have, the more of those
photons you can collect, youhave a larger light bucket.
There is, though, a limit tothat, especially in terms of the
residence fluorescence LiDARs.
The residence fluorescenceLiDARs, actually, I mean,
they're like it's almost like afluorescent material in space,
(21:46):
kind of like a laser, for themost part kind of up in the
atmosphere, and so you know, ifyou put out too much of the
laser signal, hoping to getreturns back, you can actually
saturate the layer, and sothere's going to be a limitation
, potentially, to how muchsignal you can get back,
regardless of the size of thetelescope.
Speaker 2 (22:06):
Wow, yeah, I was just noticing how many different
parts of electrical engineeringcome into play to make the LiDAR
work, everything from optics tosignal processing.
Speaker 4 (22:22):
Yes.
Speaker 2 (22:23):
I'm curious if I were to dig in a little deeper into
the laser itself.
You mentioned very highkilowatt lasers.
Could you talk a little bitabout the challenges and
complexity of building suchlasers?
Speaker 4 (22:40):
Oh, certainly.
Of course, the laser itself iscomprised of many components.
There's different ways toachieve laser technology.
One it could be based on itcould be a traditional laser
that's based on a resonator, and, you know, you kind of achieve
high power that way.
Other approaches are to createthese master oscillator power
(23:02):
amplifier type lasers, where youstart with a seed laser,
perhaps a relatively low power,and then you amplify it.
In fact, both of the systemsthat we're building are based on
that technology.
The helium LiDAR is nothingmore than a semiconductor laser
that's amplified by a chain offiber amplifiers, and then our
(23:26):
sodium system is based on Ramanscattering in bulk crystals.
In that case, again, it'samplifiers that are amplifying
our signal, and then at the endwe double to get the 589 from
1178 nanometers.
To get to the high power, thereare several things that of
course we have to think about.
One is you have to energize, orprovide energy to the laser.
(23:50):
So the pumps, as we call them,have to provide sufficient power
in a wavelength range that thegain material can absorb.
That's basic lasers 101.
And then you have to considerthe modality or the framework by
which you're actuallygenerating the light.
So, for instance, in fiberlaser systems we're after the
(24:16):
high power, and for our heliumsystem we want to make sure that
our laser wavelength not justthe wavelength but the spectrum
of that laser lies within theabsorption band of the helium.
Turns out that in the upperatmosphere that's on the order
of something like a gigahertz.
This is all a temperaturebroadened stuff, but anyway we
(24:38):
want to make sure that our lasersignal is the spectral
bandwidth is much less than theone gigahertz.
Turns out that in opticalfibers this leads to
nonlinearities, in particularstimulated brillo on scattering,
which is an interaction betweenthe light wave and an acoustic
wave within the fiber.
That can greatly limit theamount of power that you get out
of it.
So it's not so much that youwant to get the power out of it,
(25:01):
but you have to then devise anoptical fiber that can also
support that kind of powerlevels while somehow
circumventing the effects ofbrillo on scattering.
There are several ways to do it.
It might be beyond the scope oftoday's discussion, and then on
top of that, of course, are allthe optics, and so normally
(25:24):
when we send a beam out, ifwe're going over long distances
it's different of over shortdistances, but maybe we don't
want the divergence to be toolarge, because as we come up
through the atmosphere we don'twant to have our beam expanding
to many hundreds of kilometersin the far field, and so what
we'll do is to reduce thedivergence.
We'll do a beam expansion andof course all of the optical
(25:47):
components that go into thatexpansion then have to tolerate
that kind of power.
So there are a lot of differentthings that we think about.
And then ultimately, as we'rerunning, we think about device
longevity.
Are there components to thatsystem that might fail over time
, especially when you're doingsomething like a remote
(26:07):
measurement, or you're sending alaser system onto an autonomous
vehicle or even a rocket,because I wouldn't call that
necessary.
It's autonomous, I guess, in away, but if you're just
launching and it's doing itsthing, you want the system to
succeed and not fail during itsflight.
And then, on top of that too,of course, when you're on a
(26:29):
platform such as that one, youthink about vibrations, things
shaking.
What's interesting about thatsystem is it's not so much
making the measurement once weget to the layer that we're
interested in the sodium layer,it's the ride that it takes
getting up there, and so whenthings are shaking, it has to
survive the ride.
Once it gets to the layer,everything's nice and smooth,
(26:49):
all the rocket engines shut offand it's not a big deal.
But then we also think aboutmaking sure that the wavelength
itself is stable enough again tobe held within the absorption
band of interest.
There are temperaturefluctuations, vibrations and
things that are happening.
There's a possibility of thewavelength walking off For
(27:10):
systems with motion, such as therocket.
Now we also have to contendwith a Doppler shift.
So the fact that our rocket ismoving gives us another degree
of complexity, in that we haveto understand not just the
wavelength, but how does theobservation change, given the
fact that the rocket itself ison a moving platform?
Speaker 2 (27:30):
Wow yeah, there are so many layers of complexity
that you just went through that.
I want to peel away a littlebit and ask you a little bit
more detail.
The stimulated balloonscattering is an incredibly
fascinating phenomenon and Ijust want to clarify with you.
(27:56):
It is the.
Where does the acoustic wavearise from?
In the fiber.
So let's start there.
I have so many questions aboutwhat you just explained.
Speaker 4 (28:07):
Oh sure, sure.
Well, I guess the easiest wayto think about it, the simplest
model, is to consider the fiberitself as being at temperature,
it's just room temperature.
Whatever it is, there arevibrations that are present in
the material, and so you couldthink of sort of the glass
itself as being kind of a bathof acoustic waves that are all
(28:32):
present.
And as the light wave passesthrough the optical fiber, there
will be bragg mesh with some ofthose acoustic waves, as your
bragg.
The acoustic wave itself, ofcourse, is a longitudinal
pressure wave, and if you havepressure in the material, that
changes the refractive index,and so the grading itself looks
a lot like a fiber bragg rating.
(28:52):
And so your optical wave, whenit comes in, will be bragg
meshed with some of thoseacoustic waves.
Again, one in principle.
But the optical fiber can be anacoustic wave guide and it can
actually interact with multipleacoustic waves and so on and so
forth.
But to keep it simple, thelight wave will then, will
(29:12):
scatter from that bragg-matchedwave.
The scattered light wave willthen well, it's also Doppler
shifted, by the way, because thesound wave is moving at the
speed of sound.
So you have a frequency shiftassociated with that reflected
wave.
That scattered wave then willinterfere with the original
forward-going wave.
That interference pattern thenfeeds that original acoustic
(29:33):
wave, because now the originalacoustic wave becomes amplified,
its reflection becomes stronger, and so you can kind of see
this positive feedback cyclesort of forming.
Eventually you reach some powerthreshold known as the threshold
power, I guess where yourstimulated process takes over
from noise and instead ofgetting light out of the fiber,
(29:57):
much of it gets reflected backtowards the center.
So it's a problem that you seenot only in lasers but also in
telecommunications.
In telecom the easiest way toavoid this problem is to broaden
the spectrum, as Brillouinscattering is a coherent process
that requires a line widththat's less than the Brillouin
line width, which is usually onthe order of tens of megahertz.
(30:19):
For us, for the LiDARapplication.
Oftentimes we're not allowed todo that, because we're trying
to make sure that our lasersignal lies within the
absorption bandwidth of thespecies we're trying to measure.
Speaker 2 (30:33):
I see, wow, very cool .
The second topic I wasinterested in was the.
You know, it's prettyincredible that you're working
with these huge powers and I'mcurious if you can comment on
how, practically speaking how,these experiments are done in a
university lab.
I'm sure there are someinteresting challenges there.
Speaker 4 (30:58):
Yeah Well, safety is an utmost concern, so making
sure that the students are awareof their goggles and all that
stuff.
Actually, if I could take aside note before we move on, yes
, of course.
We actually have partners thatdo that.
We partner with Air Force andother groups that do kind of the
(31:24):
high power building for us, andso we don't.
One of the things that I try todo make sure that you know it's
a lot to ask a student to becomfortable about, you know,
working with kilowatts, yeah, socertainly underscores the
importance of collaboration.
Yeah, so this was.
This is a side, that was a sidecomment, not meant for
(31:45):
publishing, just just if that's.
Speaker 2 (31:49):
I guess the editors would Sorry, I couldn't find the
mute button.
Yep, that's fine, peter, okay,okay, yeah.
Speaker 1 (31:54):
I also just wanted to take this opportunity to say
that it's going really good.
The podcast is so interesting,so I'm really excited about this
.
Okay, yeah, I don't know ifwe're going off topic by talking
about the FIWAR technology ornot?
Speaker 4 (32:10):
No, you guys.
Speaker 1 (32:10):
I mean, like I said, it's a conversation in lead back
and it's really interesting Meand Karen are just saying how
we're both learning so much, soyou're doing great, but I'll
just make sure.
So you just want to remove fromwhere you said to the side note
right, yeah, yeah, yeah, yeah.
Speaker 4 (32:25):
No, I mean like I said, we We'll go up to 100
watts, a couple of 100 watts,but that's sort of where I like
to draw a line, because beyondthat point there's a real risk
for the students and unless theyhave a lot of experience
working with these things, it'sbetter if someone else is
willing to do it for us.
Yeah, here you go.
Speaker 1 (32:45):
Yeah, yeah no, that makes complete sense.
Okay thank you so much.
I took no, okay.
Okay, I'm going to go back onme.
Speaker 2 (32:55):
The other question I had was relevant to the rocket
launching, so can you talk alittle bit more about the
challenges involved in designinga laser to be launched on a
rocket Sounds incredible.
Yeah, well, we have.
Speaker 4 (33:12):
The R LiDAR system is comprised of many parts, as
we've already talked about.
You know there's the.
I guess the rocket is fairlylong and thin and when it flies
it has to fly in a way that'sstable and, I guess, predictable
.
But there are multiplecomponents that we have to worry
(33:32):
about.
So one, there is a telescopethat's on board, you know, a
curved mirror that's on boardthe rocket, and so you know when
the Actually the way it'sdesigned is as the rocket goes
up through the atmosphere, youknow different.
You know the fuel pods orwhatever will fall off the back
end.
I'm not an expert in the rocketitself, by the way, but
(33:56):
thinking about you know kind ofruggedization.
So one, you have to make surethat that telescope or that
mirror survives that process.
So actually figuring out how toepoxy it to a stable sort of
substrate such that it doesn'tcrack or shift or move out of
place, that's really important.
(34:17):
Of course the.
You know we have our mirror andthat's in a different place
from the laser.
The laser itself is on ahardened breadboard.
All the components are in, youknow machined grooves, kind of
where everything sits, you knowmechanically ruggedized and of
course, locked into place withvarious epoxies and then the
(34:41):
output of that system, of course.
Well, I should go back andcomment.
One of the things about thissetup and you know when one is
thinking about making sure thatthe laser itself stays aligned
during that flight is to usecomponents that are a little bit
bigger than you would usuallyuse in a lab.
You know it's kind of in.
(35:02):
You know it's like a typical,you know, university laboratory
or something like this teachinglab or research lab or whatnot.
So what you want to make sureis we have things like lenses
and mirrors that directdifferent parts of the beam to
different locations inside thelaser itself If something shifts
.
You know, like the crystal, forexample, the Raman crystal is
(35:25):
large enough such that ifthere's a shift in the position
it doesn't matter because thecrystal is large enough to
tolerate that change in position.
So that's part of a key to that.
The other part of it, of course, is making sure that things
stay put.
You know you want to make surethat everything is locked into
place.
(35:46):
We actually I'm not a mechanicalengineering expert, but this is
a testament to the multi, youknow, kind of multifaceted
nature of doing research likethis is.
We have people from themechanical engineering
department helping us to designthat stuff.
You know, it's very, like Isaid, very multidisciplinary.
It's like, you know, how do we?
I understand photons and Iunderstand how to generate them,
(36:09):
but how then do we drugadizethis thing?
Okay, and so that's part of the, you know, yeah, yeah, part of
the whole story.
And then, of course, as ourlaser is in a different position
from the mirror, you know we'lltake an.
You know, for example, ourconcept is to bring an optical
(36:29):
fiber, you know, to the outputof the laser, and then the
optical fiber will bring thebeam over to the telescope and
then our beam will, you knowkind of couple to the telescope,
be reflected from the mirrorand outwards in a truly
monostatic configuration.
And then that same telescope isused for receiving Another
(36:52):
optical fiber on the receiverend of course, collects that
light and then takes that to yetanother part of the rocket that
has our photodetectors, whichare actually photomultiplier
tubes, and making sure that thatstays aligned is also
imperative.
So it's, you know, there'sfibers, there's the mirror,
there's the laser, and it's thealignment of the various things,
(37:13):
plus the rigidity, thestructural integrity to make
sure that things don't breakapart, shake apart or become
misaligned.
So there's a lot to think about.
It's not a trivial task, it'sjust, yeah, a lot of things to
think about.
Speaker 2 (37:29):
That's quite an understatement.
It's very exciting and I assumethis is one of the reasons what
makes you so passionate aboutthis research, because it's
always something new to learnand problems to solve.
I'm curious just once therocket actually reaches the
(37:53):
layer that you're interested in,does it simply float?
Like are you still controllingthe motors?
Like how does it actually work?
Speaker 4 (38:04):
It's going to.
Basically it's going to ride upto roughly 130 kilometers, you
know, through its fuel that'sgoing to be on board and once
that's spent the rocket will nolonger be.
You know, it won't be propelled,it's going to undergo a
controlled fall and the way thatwe have it set up is it's
(38:28):
actually going to be spinning asit's falling.
Of course, those are the rocketscientists that figured that
out.
Again, there's a whole team ofpeople involved in this
development.
But as it's coming down it'sgoing to kind of rotate and so
what we're going to do is we'regoing to get a kind of a 360
degree field of view of thereturns or the turbulence field
(38:52):
that's in the vicinity of therocket.
Again, this isn't turbulencecaused by the rocket, it's, in
principle, turbulence-relatedatmospheric dynamics and that
fall process is actually quitesmooth.
Actually, the way they describeit is like a turbulence-free
kind of floating.
That happens, and you know wecan only measure, you know,
(39:15):
through the sodium layer whichends at about, you know, 80 to
85 kilometers or so, and thenthe rocket itself will land in
the ocean, near the shore, andwill retrieve it to hopefully
it'll survive, of course, thatprocess, the impact, so that we
can use it again.
Speaker 2 (39:34):
That's incredible You'll get your laser back.
Speaker 4 (39:37):
Well, that's the hope .
That's the hope you never know.
Speaker 2 (39:44):
So let me ask you about the another challenge that
many of the listeners areprobably aware of is, since we
are in the in LiDAR, since weare trying to measure such a
weak signal, can you talk alittle bit about the detection
challenges on the detector side?
Speaker 4 (40:02):
Certainly.
But again, you know, whenyou're designing a LiDAR system
you kind of have to have apriori sort of a sense of the
signal that you expect to getback, and that will help to
guide your choice of receiver ordetector.
The first order, of course youknow you have a wavelength that
(40:23):
you're producing and then someother wavelengths.
Maybe the same wavelength or adifferent wavelength will come
back, and you want to make surethat your receiver, of course,
spectrally overlaps with whatyou're trying to detect.
So you know, for instance, youknow if you're trying to look
for a 1300 nanometer signal witha silicon detector, that's not
going to work so good.
So of course that's the firstpriority.
(40:43):
The second is to understand howmuch power or how many photons
you expect to get back.
If you're expecting a largesignal to come back, oftentimes
if you're close range to anobject and it's, you know,
perhaps an automotive LiDAR youmight get a lot of signal back,
and so you can use a standarddetector for something like this
(41:04):
, whereas if you are expectingto get just a few photons back,
then we have to move to a photoncounting device.
So those could bephotomultiplier tubes.
Photomultiplier tubes work onthe photoelectric effect.
Basically, you have thismaterial, you know a photon
comes in, the energy is abovethe work function, it spits out
(41:26):
an electron and then that'samplified through a chain of
what are called dinodes and youknow you get, you know, maybe a
factor of a millionamplification.
In that case, just like withanything else, the higher the
work function, the lower thenoise that you have.
Same as with semiconductors.
You can also think about photoncounting semiconductors.
(41:47):
However, the smaller the bandgap, the more noisy they become,
as thermally generatedelectrons can traverse the band
gap.
And so oftentimes, when we'redealing with longer wavelengths,
you know where, like, the workfunction is low or the band gap
might be low, then we have tothink about actively cooling the
device.
Yeah, fortunately for us withthe sodium those wavelengths are
(42:13):
long enough, or sorry, theenergies are high enough.
The wavelengths are shortenough that we can get away with
an uncooled receiver system,whereas once somebody moves,
once you move to like 1083nanometers, where there could be
a lot of background, lightbackground and then thermal
noise, of course, in thereceiver system, then we might
have to think about cooling thedevice.
Speaker 2 (42:35):
So actually there's a question for you, Kristen how
are we doing on time?
I just realized we've gonequite a bit long, Do I?
Speaker 1 (42:43):
kind of have to wrap up yeah, go ahead.
Yeah, we have 10 minutes left.
We don't have to like stick tothe 10 minutes, but I definitely
recommend not going that muchover.
It may be just if you want topick out something that you
really wanted to make sure getsincluded, but I would try to
keep it within like 15 minutesif possible.
Speaker 4 (43:02):
Well, do you guys want to?
I've got this text written outfor, like, what are other types
of light ours?
Could that be like a goodclosing thing, or?
I mean, I wrote that outPerfect.
Speaker 2 (43:11):
Yeah, I don't know Right there yeah.
Speaker 4 (43:17):
This way I could just read it and then you know we
could.
That way, we would bring thelast 10 minutes.
Speaker 2 (43:26):
So don't we need to talk about Akhil's questions, or
no?
Speaker 1 (43:31):
Maybe like it's just Peter's 10 minutes, Sorry yeah
yeah, yeah.
Speaker 3 (43:37):
So if Peter and Rajesh could actually finish in
the next 10 minutes, then I'vegot a couple of questions and
I'll try and combine some of thequestions.
So I asked the important onesand overall we'll still stay
within the time period.
Speaker 2 (43:50):
So first let's move on to Dr Kamala, Is that okay,
Peter?
Speaker 4 (43:54):
That sounds great.
Rajesh, do you have it open?
Speaker 2 (43:58):
Yeah, I have it open, oh, okay.
Speaker 4 (44:01):
Yeah, so I was thinking maybe this kind of this
what are other types of lidars?
Just to kind of talk aboutother you know, Okay, cool.
Speaker 2 (44:10):
Okay, three, two, one .
So, Peter, so far you've givenus a fantastic description of
the challenges involved in yourspecific research.
I'm curious what are the typesof lidars exist?
And also if you can also talk alittle bit about opportunities
and where this field is going tocreate.
Speaker 4 (44:31):
Sure, that'd be wonderful.
Thanks for the opportunity.
So other types of lidars well,we've already discussed the
residence fluorescent systems.
Others are based on either theelastic or any elastic
scattering of light from theatmospheric constituents.
In the case of elasticscattering, these are based on
(44:51):
scattering from molecules oraerosols.
Usually we think about Rayleighor Me scattering in that case.
For example, upper atmospheric,such as exo or mesospheric
Rayleigh lidars are most oftenused to track dynamics in those
regions of the atmosphere.
For example, one such dynamicprocess involves gravity waves.
These are distinct, of course,from gravitational waves.
(45:11):
They relate to the motion ofthe atmosphere up and down
vertically with time.
Importantly, tracking eventssuch as these things again also
helps us understand how energycouples between the regions of
our atmosphere and enablesglobal energy transport models.
Aerosol lidars can, for example, be also used for tracking air
quality near the ground.
(45:32):
So pollution sensing and thatkind of thing.
Lidars that make use of Rayleighor Me scattering also include
something that Lidars known asdifferential absorption Lidars.
There what you do basically isyou have your laser beam again
it's pulsed, most often times todo ranging, and then you tune
your laser beams on anabsorption feature and off an
(45:53):
absorption feature, if you knowwhat the absorption
cross-section is for thatfeature.
The ratio of those two signalsgives you a relative abundance
of that constituent.
These types of Lidars can beused to measure greenhouse gases
again, such as water vapor, asI had worked on in the past, and
carbon dioxide, for instance,as well.
These two atmosphericconstituents, among others, of
(46:16):
course, can be measured in thenear infrared.
That means that we can use lessexpensive and possibly less
noisy sensors and less expensivelasers, for instance.
Other gas sensors, such asthose that look for nitrogen or
sulfur oxides, require lasers inthe mid-infrared, which is more
challenging from severalperspectives.
Different lasers at thosewavelengths produce insufficient
(46:38):
powers, especially if you wantthem to be pulsed Detectors.
Of course, now you're talkingabout low-band gap materials,
they become more noisy receivers.
You also have Doppler systemsthat make use of Rayleigh
scattering, but the receiver isable to measure a change in the
frequency or the Doppler shift.
These systems are oftenactually these days commercially
(46:59):
used to measure wind speed inthe vicinity of wind turbines.
Other LiDAR technologies basedon any elastic scattering are
like Raman and Brillouin lasers.
Like Doppler LiDARs, thesesystems rely on the measurement
of change of frequency of anoutgoing laser signal, of course
after interacting with themeasure end.
For instance, we talked aboutBrillouin scattering.
Brillouin scattering is aninteraction between a light wave
(47:22):
and an acoustic wave,oftentimes ultrasonic or
hypersonic.
The light scattered byBrillouin scattering, just like
it is an optical fiber, isfrequently shifted, and this
frequency shift can be a verystrong function of environmental
things like temperature.
Just as a result of this, forexample, brillouin scattering
based LiDARs have foundapplications in ocean
(47:43):
thermometry, which becomes avery important thing to measure
Again global circulation models,not in the upper atmosphere but
in our oceans.
Lidars can also operate in boththe time and frequency domain.
We talked about pulse LiDARs,but the time domain systems are
pulsed Again.
These are time of flightsystems.
Frequency domain LiDARs, on theother hand, use frequency
(48:04):
modulated continuous laser,where the laser wavelength is
swept in time.
There part of the output beamis taken as a reference or a
local oscillator.
Then think about like you senda signal out.
If our frequency is constantlyscanning or sweeping, then the
time delay between what comesback and the local oscillator
(48:25):
will give rise to a frequencyoffset between those two things.
Then, of course, if we beatthem together and measure the
frequency shift, that gives usthe time delay or equivalent of
the distance.
Lots of different ways to dothis.
As far as opportunities andbottlenecks and things go.
Challenges again, there are alot of challenges in the
(48:48):
development of LiDARs.
This is related to the laserwavelength and power.
Going back to the automotiveLiDAR application, ice safety
becomes a concern.
Ice safety is a verysignificant, a very serious
limitation to the feasibility ofLiDAR systems.
Again, we want large telescope.
(49:08):
Necessarily.
We want high power.
You can't think about reallyputting power out that might
damage someone's eye.
You also can't imagine puttingone meter telescope on top of a
car.
That's one way to think aboutlimitation.
Again, low noise, highefficiency receivers can be a
(49:29):
challenge.
We talked about silicondetectors that have been
developed for many years, a verymature technology.
Dynamic range available fromthem is also very large.
You can do photon counting withsilicon all the way up to high
power measurements.
But if a desired operatingwavelength lies outside that
spectral response of silicon,different materials have to be
(49:50):
used.
Again, some of these thingsaren't then amenable to photon
counting.
We have to think aboutdifferent ways to detect these
signals, such as a modern pushtowards things like far infrared
, superconducting, single photonreceivers.
Anyway, a lot of opportunitiesin new lasers, new receivers,
(50:13):
autonomous operation, of course,power, more efficient solutions
are important.
We think about all those thingsas well.
Again, as we talked about theenvironment and the platform on
which the laser is placed or theLiDAR is put, it's going to be
a serious limitation.
Speaker 2 (50:29):
Wonderful.
Thank you, pete, so much forspending the time going through
lots of the details about notonly your project but also an
overview of the opportunitiesand all the excitement around
LiDAR technology.
I have certainly learned a lotand enjoyed this conversation
(50:49):
very much.
Now I'd like to pass the batonto Akhil for the remainder of
the podcast.
Speaker 3 (50:57):
Thank you very much Rajesh, thank you very much
Peter.
That was absolutely incredible.
The amount of things that we'veactually had a conversation
about and so much of what we canunpack through the course of
the podcast and afterwards isincredible, and I thank you both
very, very much for that.
I've got a couple of questionsbefore we close for today, and
(51:19):
the first question I'd like tokeep for a minute Peter, both
interested.
Now, obviously, as I havelearned, being a PhD student and
an early career researcher anda postdoc, the first thing you
do when you start talking tosomebody is you Google them and
you find out what they actuallydo.
Now, interestingly, with mybackground in biophotonics,
(51:39):
everything that Peter does interms of time of flight imaging,
in terms of time of flightsensing, lidar systems, low
light conditions for LiDARsystems specifically, all the
scattering methods, everythingare also seen in Rajesh's
research of brain imaging.
Do you ever see the crossoveracross the fields?
(51:59):
Do you think something in LiDARsystems would be interesting to
Rajesh and do you thinksomething in biomedical optics
would be interesting to Peter?
A question to the most of you.
Speaker 2 (52:12):
Peter, you want to.
Speaker 4 (52:17):
That's a very interesting question because
although the different fieldsuse different names, different
words for technologies andmethods, a lot of the approaches
are all identical FMCW, forinstance, LiDARs, which you find
at automotive, LiDARs,automotive, autonomous vehicle
(52:41):
sort of things.
The same technology can befound in precision metrology on
the micro scale, so that couldalso include bio applications
and bio imaging things.
Speaker 3 (52:59):
Because it's quite interesting, when Peter was
talking about everything he wasmentioning, he was talking about
fluorescence, about LiDAR,about valence scattering, all of
which I'm sure Rajesh andmyself have seen in tissue
imaging.
So, rajesh, you were about tosay something.
Speaker 2 (53:18):
Peter's exactly right .
I think there's a significantamount of cross talk and it's
one of the reasons I try toactually talk to folks outside
of my discipline is that you notonly recognize areas that are
common but new ways of solvingvery similar problems.
(53:38):
So in dealing with scattering,certainly in macro scale imaging
, people have applied TemuFlightfor imaging through scattering
media in the microscopycommunity because the dimensions
are so small that the timedifference of the reflector
pulses are way too small, atleast as far as I'm aware of.
(54:01):
I think it's quite challenging,but I wouldn't say never, but
it is a little more challengingthan doing it for much larger
distances, I would say.
But it feels like adaptiveoptics clearly have been applied
in both areas.
Biophotonic adaptive optics ispretty standard nowadays, but it
(54:25):
was adopted originally fromastronomy and I have completely
different fields.
Speaker 3 (54:35):
Absolutely.
I mean there is obviously.
There's a big difference,literally, between a mirror used
in the telescope and a mirrorused on a digital micrometer
device, but we're stilleffectively still using a mirror
.
Speaker 2 (54:47):
Right, right yeah.
So, it really underscores the Ithink it's an important point
that you're raising.
It underscores the importanceof understanding the
fundamentals of whatever it isthat you're learning, because as
an engineer or scientist, it'smuch easier to translate your
(55:10):
skills to very different fields.
I think it's an important pointto convey to the young
engineers and scientists who arelistening to this.
Speaker 3 (55:19):
Absolutely.
My next question again to theboth of you is, as quickly as
you can and as easily as you can, what are the two things, one
for a academic sphere and onefor a personal?
Or?
Here's a good advice to be agood researcher.
Kind of advice would you giveto somebody listening to this?
(55:41):
Where should the next LiDARsystems engineer focus on?
Also, what should every youngresearcher try to do right now?
And maybe, Peter, would youlike to go first?
Speaker 4 (56:00):
Ah, boy okay.
Speaker 2 (56:07):
I can go first if you want, I mean.
Speaker 4 (56:10):
Please, maybe you'll give me some ideas.
Speaker 3 (56:13):
It's just a question of all of us being very polite
with each other.
So, Radis, how about you gofirst?
Speaker 4 (56:20):
Well, we can edit these things out, right.
Speaker 2 (56:22):
Yeah, exactly, I'd say as a new I don't want to use
the word young, because you maynot be young in mind, young in
a field, person entering a field.
I think it's really importantto really talk to as many people
as possible to understand thelandscape and understand the
(56:43):
challenges often which are notnecessarily obvious or even
written down somewhere.
So it's really useful tounderstand the culture and the
challenges of a field as much aspossible, and the way I think
it's an effective way tounderstand it is, of course,
talk to your peers, talk to yourmentors, talk to your competing
(57:07):
labs, if there are any, go toconferences.
Really try to talk to as manypeople as possible, even if
they're not directly related toyour field.
You learn a lot.
This means my personalexperience.
Speaker 4 (57:25):
Yeah, I can actually follow up on that.
I agree entirely with thatremark, Rajesh.
You did your undergrad at MIT.
Speaker 2 (57:40):
My graduate work, but go ahead.
Speaker 4 (57:42):
Sorry, your graduate work?
Yeah, we can start over.
I fully agree with the commentsthat you made.
Those are very important points.
I fully support them.
I guess you did your graduatedegree at MIT.
Do you have familiarity withOlin College's user-oriented
collaborative design course?
Speaker 2 (58:04):
Unfortunately not, sorry, please go ahead.
Speaker 4 (58:09):
I actually had the privilege of teaching that as a
transplant here at the U of Ifor a few semesters.
It was taught within the Artand Design program, and Olin
College actually teaches that asa very first semester freshman
course to kind of help studentsunderstand how to go out and
find problems.
It's not so much finding asolution to a problem, but it's
(58:31):
going out and understanding howto find where the problems exist
.
What's a problem?
A problem is something thatcould make someone's life better
.
A problem could be somethingthat helps us understand our
environment better, Anywherewhere you feel like you might be
able to make a positive changefor humanity.
And unless you're able tounderstand how to go out and
(58:52):
find those problems, it's hardto understand whether the
solutions that you're generatinghave any value or have any
meaning.
And so I agree the whole idea.
That course that I was involvedwith actually got the students
up out of the classroom into thefield talking to people.
Hey, what do you think isimportant?
What could make your lifebetter From the perspective of a
(59:15):
LiDAR system?
What is it that we need tounderstand to really get a grasp
on the meaning of globalwarming?
For instance, Do we have tomeasure carbon dioxide?
Or is there an atmosphericmodel somewhere where there's a
scientist who's not a laserperson who says, hey, if we had
this information, this would betransformative, and so the
(59:37):
student then can go out findthat problem and then speak
targeted solutions to solvingthat problem?
Speaker 3 (59:45):
I think that's a very interesting perspective and
interesting advice as well,because somebody I look up to
quite a lot, in addition toeverything that you've mentioned
, has also quite vocally saidthat sometimes the people that
you actually work with arealmost as valuable, if not more,
than the actual problem thatyou're trying to solve, and such
(01:00:06):
is the nature of academia, suchis the nature of industry, such
is the nature of everythingthat we do today, that the
people that we work with add somuch more value.
So, going back to Rajesh'sadvice of speaking to more
people, building thoseconnections, and combining that
with Peter's idea of the here'sa problem I would really really
like to solve makes up for sucha perfect motivational statement
(01:00:29):
.
For instance, where anyonetaking on a project, a research
problem, across any field,really and I think if you'd
actually seen me on video whilewe were having this conversation
, listening to the both of you,I was simply going yep, they've
answered that.
Yep, they've answered that.
Yep, they've answered that.
So you've left me with almostno questions to ask, which is
really really good.
(01:00:53):
I'm going to end today bythanking you both for your time.
It's been a wonderfulconversation.
We have heard about LiDARsystems, about how margin
atmospheres can be measured andmonitored, the value of it for
astronomy, looking atfluorescence, looking at low
light problems.
We touched a little bit onbrain imaging, although that's
(01:01:17):
tangentially related.
However, as in research,everything is connected.
I think one of the biggesttakeaways for me was how
multidisciplinary andinterdisciplinary research today
and problems today have become.
There's electronics, there'soptics, there's rocket science,
and I never actually, and neverbefore today, have I realized
(01:01:39):
how much someone like Peterwould really like his laser back
after it's gone to space andcome back.
So I think that's quite nice Ajourney of a laser that's
probably traveled more than me.
Speaker 2 (01:01:54):
I do have one last question for you, Akhil.
Speaker 4 (01:01:57):
Yeah, go ahead.
Speaker 2 (01:01:59):
Before we end, what are some key takeaways that we,
as more advanced in the careers,should know how we can support
early stage researchers likeyourself and your peers.
Speaker 3 (01:02:18):
Okay, so how much time do you have?
How could I list, so, I think,the conversations that people
can have?
There is an innate fear, whenit comes to every early career
researcher and PhD student, towalk up to an established
academic at a conference and gohere's a question I have.
(01:02:41):
I read a paper that youpublished and I think I have a
few questions.
Would you have an opportunityfor a conversation?
I think the, as in mostacademics and most sorry, I
correct myself most early careerresearchers are looking for a
(01:03:01):
mentor, somebody who can eitherbe a mentor for a long duration,
somebody who's going to who'sat the other end of their career
to turn and say I will guideyou through this procedure, or
somebody who can answer thequestion as best as they can in
that moment, effectively helpingthem along their journey.
I think the best contributionsI have had from established
(01:03:26):
academics, from their careers tomine, was simply time, just the
opportunity to talk to somebodymuch further along in the
journey and for them toeffectively tell me I did this,
don't do this or I did this.
I think you should also do this.
I think there's no bettersupport than a good mentor, some
(01:03:48):
good advice and a generoussupport of nature really, so
does that answer your question?
I've got a bigger list, though.
Excellent.
Speaker 2 (01:03:56):
Excellent.
No, that's a fantastic place.
I've got a bigger list thatsays sorry, go ahead.
Speaker 3 (01:04:05):
No, no, no, go ahead.
I've got a bigger list that'sgot cameras, lasers, optic
systems.
I'm going to put Peter Linersystems on it.
It's a shopping bag.
Speaker 1 (01:04:17):
That was so, so good.
I think that might don't tellthe other participants, but
that's like my favorite episodeso far.
So thank you so much, I think.
Karen Karen did you want to aska question?
Speaker 2 (01:04:27):
It was my first and I'm hooked already.
Speaker 3 (01:04:31):
I found myself taking notes and, like I don't have a
clue, but this is so interestingI have to write something down.
Speaker 2 (01:04:36):
but, pete, you had said when they said what got you
into this, you said it wassomething you did in your
undergraduate group work or astudy group and that took you
back there.
Speaker 3 (01:04:48):
Can I ask whose?
Speaker 2 (01:04:48):
group that was.
Speaker 4 (01:04:50):
George Papin, okay.
Speaker 2 (01:04:53):
I said to Kirsten, I said it has to be one of our
guys, because at one point ourentire bog was almost from, you
know, Urbana Champaign.
Oh yeah, we have to know who itwas.
Speaker 4 (01:05:07):
I don't know if George was ever on the bog, but
we've got.
I mean, ken Chiquette is in theoffice next to mine.
Speaker 2 (01:05:14):
He was president at some point, yeah.
Speaker 4 (01:05:18):
I know George from other things, but like we, I
mean you know we oh yeah.
Yeah, jim, and yeah, it'sinteresting, because you know
what one regret that I have isthat George's advisor was Bahasa
.
Okay, I've actually never methim.
Speaker 1 (01:05:37):
Oh man.
Speaker 4 (01:05:39):
My grand advisor, or whatever you call it.
Speaker 1 (01:05:46):
Is it Gary Eden?
There too?
Speaker 4 (01:05:48):
Hey, gary is here.
Yeah, he's retired recently.
He's spending more of his timein Texas these days, kind of in
retirement, but yeah, yeah,gary's here and.
Speaker 2 (01:05:56):
You know that's such a thing.
Does everybody from Illinoiseventually head to Texas?
Because there's?
Speaker 1 (01:06:01):
a couple of them I know Shu Ling.
Speaker 2 (01:06:04):
Everybody went to Texas, Yep.
Speaker 4 (01:06:05):
Yep, yep.
So yeah, I don't know what'sgoing on.
Speaker 2 (01:06:12):
I guess you know they've got their oil field
endowments, I guess they're onpump.
Speaker 1 (01:06:18):
Yeah, that's hysterical.
Um, okay, all right, so we're15 minutes over, so I know how
you guys gave so much air freetime, so I'm going to wrap it up
so you guys can get some timeback.
But I just want to justseriously tell you guys how
grateful and how much weappreciate you participating in
this, and we probably will askfor you guys to come back as a
(01:06:39):
moderator or guest speaker.
So just keep your eye open andI'll let you guys know as soon
as the episode is you know hasbeen edited by our editor, and
then I'll let you guys know assoon as it's up on Spotify as
well.
Excellent.
Speaker 3 (01:06:56):
Thank you, thank you very much, thank you.
Speaker 4 (01:06:59):
Thanks everybody.
Yeah, Okay, if they need to,you know to dub over anything,
because maybe my you know, SouthSide of Chicago accent was made
things unclear.
Speaker 1 (01:07:15):
But in that case I'll definitely reach out to you
guys.
But our editor's pretty goodand you guys really did like
such a good job.
You're all naturals.
Speaker 4 (01:07:23):
Thank you very much.
Speaker 1 (01:07:24):
Thanks everybody, thank you, bye, bye, bye, bye.
Speaker 2 (01:07:28):
Bye.
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