March 5, 2019 • 36 mins
What makes a laser a laser? Pew Pew Pew!? Zap Zap Zap!?
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Episode Transcript
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Speaker 1 (00:07):
Hey, Daniel, let's talk about acronyms. Acronyms are actually a
really really important part of science. Whenever you have a
good idea, you have to come up with an acronym
or it's not going to be catchy. Well, I heard
there have been some pretty unfortunate acronyms in the history
of science. There are I googled for worst acronyms ever,
and I came up with some that you gotta wonder,
(00:27):
like people must have known what was going on, you know. So, um,
one of my favorites is Phase one Observing Proposal System.
So for those of you filing along at home, that's
p O O P S. So yeah, you can put
that together yourself. But but I heard that one day
actually grabbed the y from system, like they consciously made
(00:51):
the choice not to be called poops but to be
called poop. See, well, there is one acronym that's a
famous acronym for a physics topic. But I think we
think maybe most people don't even know it's an acronym. Yeah,
And maybe that means it's really successful, right, because it's
become a word in its own right. You know, people
actually use the word yeah, and that word is laser
(01:14):
camp to do. So, do you know what it stands for? Horror? Hey,
don't look it up. Do you know what it stands for?
Test NERD CREB test, I do it. It stands for
UM light amplification through stimulated emission radiation. Being we have
a winner, folks, give him a laser. But I heard
(01:35):
that the acron could have been different. It could have
been light oscillation by stimulated emission radiation. That's right, And
I don't think that one would have caught on quite
as well. That would be l o s E er
has some obvious disadvantages. You don't want to be a
loser scientist. That would be That would be obvious him
(02:14):
and I'm Daniel, and welcome to our podcast Daniel and
Jorge Explain the Universe, in which we talk about all
kinds of cool things about the universe. Yeah, and we
take the universe apart, we disassemble its acronyms, and we
tell you what it actually means. All the cool things
you see in science fiction movies, books, laser guns, stuff
like that. We break it down and make sense of
(02:35):
it for you. So, if you have ideas for what
you'd like us to talk about, send them into feedback
at Daniel and Jorge dot com. We love hearing your
topic suggestions. Today on the program, we're going to be
talking about lasers, lasers. How does a laser work? What
(02:57):
is a laser? Who came up with a laser? Where
can I at my laser death ray? These are important questions.
How can I make it my living to laz about?
Here a cartoonist, you're already laser by which I mean
you are brilliant and cutting. That's right, and very um focused,
(03:18):
very focused exactly. So, Yeah, lasers are. Lasers are awesome.
Everyone knows what a laser is. My kids know what
lasers are. Yeah, I mean they're they're in science fiction everywhere. Um,
people have laser pens, right, lasers there. You probably have
dozens of lasers in your house, right, Lasers used for everything? Yeah,
they're in our everyday lives. Like every time you go
(03:41):
buy something at a store. Assume you still go to
physical store. But if they scan your product in they're
using a laser, that's right. And if you still have
a CD player, that thing is read by a laser.
A CD what you're too young to understand those things?
For he For those of you under forty we used
to store music on these shiny little disks. Yeah, they'd
(04:02):
use lasers. So they were literally everywhere. I mean, there
are optical drives, right, anything that reads the disc. So
if you pop in a disk to your PlayStation, that's
using a laser in there, that's right. And lasers have
an enormous variety of applications, you know, from tiny laser
pointers to world size lasers that people are experimenting with
to try to deflect asteroids that might blow up the Earth. Yeah,
(04:26):
like in the Dead Star and in Star Wars, right,
that's right. Those that's the fiction, of course, But the
group building a laser to disflect asteroids, that's real. They
might save the planet. They might save the planet exactly.
So lasers are everywhere. They're definitely an important part of
our culture and of our technology and of everything you do.
(04:47):
But the question we had was how do they do
what they do? What does it mean to lazy? How
do you build a laser? Could you assemble one from
the stuff in your kitchen? Yeah? Can you shoot it
in the movies like to destroy other specihopes? That's right?
Do they really make the pew pew pew sound. That's
that's the question. I want to know the answer to
what sound does a laser make? Is it like pure
(05:09):
or it's definitely one of those? How good? I hit
it on my first three talk tries. But we were
wondering how many people out there know what a laser
is and how it works. I walked around on campus
and I asked people, do you know how a laser works?
Does of you listening think about it for a second.
(05:31):
Here's what people had to say, mate, Sorry, uh, focused light,
light gets multiplied and focused? Okay, cool light? All right.
I guess not a lot of deep knowledge about lasers
out there. I had the impression people think lasers are
(05:52):
like you have a light bulb and then maybe you
have a lens to focus it, and that's your laser.
I like the person who said, how did how do
lasers work? By light? Technically? You're right, you can go
wrong with that answer. That's right. Yeah, go with a
very very general answer, how does this work? Physics? Right?
You could just say physics to any question to ask people? Really,
(06:12):
even math? Can I say how does math work? No?
But that's not a topic for our podcast, right because
math is outside the universe. Beyond the scope of this podcast.
That's right. But maybe it's the only thing more fundamental
in physics is math. Maybe. I like how you say, maybe,
is there is there anything else? Maybe philosophy. I guess
(06:34):
philosophy and math, you know, down there at the at
the down in the dirt and the roots of human
intellectual exploration. Yeah, so lasers are pretty interesting, right, They
have an interesting history, Like apparently historians don't really know
who invented the laser, or they haven't settled on who
(06:55):
invented laser. That's right. And I heard that one really
important science historian actually wrote a him about it once.
Oh really is that true? Yeah? His name is Um.
Hold on, I have it here. Let me check Jorge him.
Oh yeah, that comic laureate of the Internet. Should we um?
Should we read the poem? Sure? Go for it. I'm
(07:17):
not sure if this is supposed to be set to
music or rhyme. Yeah, it's supposed to be said to
laser music. So you think, think eighties here and then
go for it. Um. So, I wrote this when the
laser turned fifty about eight years ago, was the anniversary
(07:37):
of the laser. I'll read it and you make the
pu pu sounds all right. The laser turns fifty this week,
an important event in history. But who developed this amazing
technique that's still kind of a mystery. Was it Ted
my mom who built the first laser? Or was it
Towns in Shacklow who wrote the seminal paper and it
(07:58):
goes on like that role beautifully crafted versus oh thanks,
Yeah it was you know what happened? I was in
Ottawa and I went to visit they have a laser
institute at one of the university there, and they explained
to me that the anniversary of the laser was coming up,
and so they explained to me how the laser works.
And in fact, I think that's kind of related to
(08:19):
how you and I started working together, right, Yeah, you
just reminded me of this today. Apparently your comic about
the laser is one of the ones that I read
and uh and induced me to write you an email.
So yeah, the history is kind of funny because the
Nobel Prize for the laser, the first prototype for the laser,
and the first paper about the laser are all credited
(08:42):
to different people, Like, nobody knows who invented this really, yeah,
it might have been one of these things where like
an idea that whose time has just come, you know,
we're on the cusp is sort of the next thing
to happen, and a few people contribute bits and pieces here,
and some other person puts these things together first there,
and uh, it's a bit of a mess. Yeah, it's
a bit of a mess. I think it's fascinating. Also
(09:03):
how important it is to assign credit for things like
we have the laser. It's awesome. Are people just fighting
about the money, like who earns a penny every time
they make a laser pointer? Or is it about like
the credit and scientific history? You know, it's it's interesting
to me how how long and nasty this battle is.
You mean you wouldn't fight to have that in your tombstone?
(09:24):
Daniel Whiteson invented the laser? Who would? Oh, I'm definitely
putting that on my tombstone. True or not? I mean,
you can put anything you wanted your trimstone. Nobody fact
checks tombstones. It's like fake news applied to tombstones. I'm
taking credit for all sorts of stuff in my tombstone. Well,
let's get into what Daniel is a laser? Right? So
(09:48):
a laser is different from a flashlight, right, It's not
just a flashlight with a lens, Okay. A laser is
something that produces a bunch of light, usually of the
same color or so, like all a bunch of photons
of the same energy, and they should all be going
in the same direction, right, So they're perfectly parallel. Meaning
(10:09):
if they're like, you know, a tiny distance apart now,
then a hundred meters away or a kilometer away, or
a million miles away, they'll still be the same distance apart,
perfectly parallel, perfectly parallel photons, right, yeah, exactly, So photons
usually of the same color, shot perfectly parallel, and also
(10:29):
wiggling the same way. Right. Remember, the photons are waves,
and they're like all other particles. They're governed by their
wave equation, and waves wiggle, right, they go up and
they go down, they go up and they go down.
And if you have two waves, if they're wiggling in
opposite directions, one wiggles up the other one wiggles down,
then they can cancel each other out. Right, So we
(10:49):
want our photons all wiggling the same way, so they
all sort of pushed together. It's like folks, on a
boat rowing at the same time. They all push together
for constructive interference to make a strong when they hit
something at the end. You want them to be perfectly synchronized.
Otherwise they might cancel each other out when they hit something. Yeah,
that's right, or they might you know, cancel each other
(11:10):
out part of the way. Um. You know these things,
these interference effects depend on the phase, and so yeah,
you want them all pushing in the same direction, um
at the same time. And so that's what a laser produces. Right.
That's that's what it means to be a laser. And
that's an important distinction of people to understand. That's not
just like a powerful flashlight or of uh flashlights somebody
put a lens in front of. It's a It's really
(11:31):
a very different kind of source of light. It's not
just a really bright light. It's like a perfectly ordered,
perfectly parallel beams of light. That's right. And there's two
kinds of lasers. One kind is the kind we're talking
about where all the photons have the same color, so
it's monochromatic, right, it's a single color of light, all
the photons of the same energy, the same color. UM.
That's the kind that you make to produce beams. You
(11:53):
can also produce laser pulses, right. These are short bursts,
and those require having lots of different colors so that
you add they add up and cancel out in just
the right way to have a localized burst. And you
can add up all the different wiggles together to make
the burst of any shape you want, right. And that's
different than a flashlight, because a flashlight it's just pumping
(12:15):
out photons with all kinds of colors and all kinds
of phases, and they're all out of sync with each other,
all these photons, that's right. And also they go in
in all different directions, right. Um, a flashlight usually has
like a tungsten filament bulb or something, right, and that's
just glowing and it's sending light in every direction. And
even if you have it, you know, coming out of
(12:35):
the front, so it's a little bit um shaped. You know.
You can take, for example, a flashlight and you can
point it at the moon, right, and as as you
get further away from the source of the light, the
size of the beam grows. Right. Flashlight makes a cone,
and the cone grows with distance, So you can point
it to the Moon, and you basically cover the whole
Moon with your flashlight, because by the time you get
(12:57):
to the distance of the Moon, the cone is huge.
Even if you focus it with like a lens and
try to get them parallel, they won't be perfectly parallel
exactly right. There's always going to be some spread there.
Whereas with a laser. If you take a laser and
you point it at the moon, if you if it's
a good laser, when it gets there, should have the
beam should have the same with is when is when
it left. So that's how that's why lasers are powerful, right,
(13:22):
because with just a few photons they can go a
great distance together and so they can transmit that information.
But they're also kind of in sync so they can
deliver all that power when they get there. That's right.
And that example about a laser to the Moon is
not just like a made up example. I don't know
if you know, but the astronauts who visited the Moon
left mirrors on the surface of the Moon so that
(13:44):
we can bounce lasers off of them and use that
to measure the distance from the Earth to the Moon.
I think that's pretty cool. The Earth's beak is selfie.
You can think we can take a selfie by shooting
the laser at the moon. And that's right. Even though
this is decades before the concept of selfies, it was
it was prescient that way, right. They were forward, forward looking.
(14:06):
NASA is always looking into the future. NASA invented the selfie.
We just we just give credit. We just give credit
to them. They can put it on the Actually the first,
the first selfie comes from decades and decades before that.
But but yeah, the first astronomical selfie for sure, first
laser selfie, that's right. Okay, So that's what the laser is.
(14:31):
It's like, it's like something that makes light, that shoots
light that's perfectly in sync and perfectly parallel and that's
really powerful. Okay, so what why is it called laser?
Like what what? What does that acronym mean? Light amplified
by stimulated emission radiation. That's right, let's break that down, right.
The first one is just light. Okay, so photons are light,
(14:52):
that's obvious. The last one, the last one is radiation, right,
and radiation in this case also it just means light. Yeah.
I think that's because they didn't want to call it
a laser that would have been more awkward with an
l So both of those words light and radiation just
(15:16):
refer to the photons, right, Okay. So it's something that
makes light, something that makes light and um and it
makes it in this special way using this process called
stimulated emission. Okay. And that's the really the guts of
the laser. That's what's going on inside, is that it's
a system that creates this stimulated emission. So we should
dig into that. The A and laser beings amplified, meaning
(15:39):
you're not just making that use sort of amplifying it somehow.
That's right. The basic principle of the laser is you
start with one photon of the color that you want,
you know, and you amplify use that to use this
system to multiply you. So I want to start with
one photon and then you create a chain reaction that
gives you ten photons, and then a hundred photons, and
then a thousand photons, etcetera, etcetera. Grows exponentially until you
(16:01):
have a very very intense beam of photons all the
same kind. And the key is the stimulated emission. That's
the thing that basically copies the photon. It says, if
you have one of the right wavelength or to all
the right attributes, then I can make more for you.
That's this process called stimulated emission. Okay, let's get stimulated
by stimulated emission. But first let's take a quick break. Okay,
(16:36):
So laser is something that makes light that's all the
same color, the same wavelength, the same direction, the same wiggle,
and it's all done by something called stimulated emission. What
does that mean? Right? So the thing that's doing the
emission is just an atom, and so you have some
medium in your laser. Maybe it's a crystal, maybe it's
(16:57):
a gas that doesn't really matter, but it's a bunch
of atoms. And atoms can emit light, right, any atom,
any atom can emit light. Right, you make you get
things hot and they glow, right, that's something emitting light.
So if you pump energy into some material, right, it
will absorb that energy and bring it internally into itself.
But then sometimes it gets rid of that energy. That's
(17:19):
called emission, and it turns that energy into light. And
the way that it does that is it has inside
it, it it has these electrons. Right, So every atom has
electrons whizzing around it, and there's electrons have a few
certain orbits that they can use around the atom. It's
like a bunch of different energy levels. Electrons can't just
have any random energy level around it atom. Based on
(17:41):
the shape of the atom and the configuration of the protons, etcetera.
There's a few places the electrons are allowed to live,
so they're called energy levels. And you can imagine sort
of a ladder of these energy levels. And that's kind
of related to their wave nature of electrons, right, because
their waves they can only fit in so many ways
around the atom. Right, It's sort of related to that, right,
(18:03):
It's very closely related. Yeah. Um, the reason that there
are discrete energy levels, right, quantized energy levels, is precisely
because of those waves and the way the waves fit
together around the atom. So a simple way to think
about it is when the electron goes around the atom,
it's going to do it's wiggling, and you wanted to
build on itself. You don't want it to cancel itself out,
(18:23):
and so when it comes around one orbit, you need
to be in the same place in its wiggle either
it's wiggling up or it's wiggling down. It has to
fit a very specific number of wiggles in an orbit.
You can just do like three and a half that's right.
It has to wiggle once or twice or three times. Right.
If it wiggles one and a half times, then it's
(18:45):
going to get out of sync with itself and eventually
cancel itself out. So those are not stable solutions. So
you can't have an electron hanging out and wiggling one
and a half times around the atom. So each of
those is a different level. It's not like the Earth
going around the Sun, like if something moves as a
little bit, our orbit will increase a little bit. That's
not how electrons work. They have very specific orbits that
(19:06):
can fit around the nucleus of the atom. Yeah, that's
actually a really interesting deep question. Is the Earth's orbit quantized?
Are there an infinite number of orbits? That's not a
one with a simple answer. If gravity is not quantum mechanical,
then you're right, so there's an infinite number of orbits
the Earth can take. However, if the gravity is quantized,
(19:27):
then then you're wrong, and there are energy levels around
the Sun, but those energy levels would be so tiny
we could probably not even see them anyway. That might
be the subject of a different podcast. Yeah, exactly. Yeah.
So the energy, So the electron has these energy levels
it has on these ladder. This ladder can go up
and it can go down. Yeah, people use the ladder analogy, right,
(19:47):
like electrons can be here or it can go up
a level or another level. Right, It's like very discrete steps.
And just like with the ladder, what happens when you
go up a level? Will you It takes some energy
to do that, right, put some energy into your thigh
muscle to push you up, and then you're storing more
energy or you have more gravitational energy because you're higher up.
The same thing happens with the electron. How does it
(20:09):
go up a level? It needs to get energy from somewhere, right,
it needs to get heated up or absorb some light
or something. So it can go up a level, right,
and then it can go down a level. And what
happens when it goes down a level While the energy
level it was at is fixed and the energy level
is going to is fixed, so the energy difference between
them is fixed, meaning every atom has the same levels.
(20:31):
And if electrons jumped down from one level to the
lower one. Then they're going to release a photon whose
energy is exactly the difference between those two levels, right,
conservation of energy. The electron loses energy, goes down a level,
and it gives off that missing that extra energy in
terms of a photon. Okay, so the electron goes down
a level, it will shoot out a photon with that
(20:53):
energy that it doesn't need anymore. That's right, exactly. So
how do you get a bunch of photons of all
the same color in the same direction. When you get
a bunch of atoms, You get them all to have
their electrons up one level, right, You heat them up,
you pump some energy into them somehow, and then you
get them to come down all about the same time.
You get them excited. You get him excited, right, and
(21:14):
then you get them the big let down. Yeah, all,
And when they get the let down, that's when they
give off a photon, and each one will give off
the same color photon. The photon is determined exactly by
its energy, which is determined by its wavelength. Right, those
things things are all connected, right, But they don't all
(21:35):
in a laser. They don't all give them out at
the same time, it's it's kind of like how you
said earlier. You want to cause a chain reaction that
will make all the atoms in your laser shoot all
these photons perfectly saying exactly so that chain reaction is key,
and you can have an atom and you can give
it energy. So the electron goes up one level and
then it's happened to just hang out there for a while, right,
(21:57):
But what happens when another photon just the right energy
level comes by, Like if you're an electron, you're an
excited state, um, and there's like a ladders step ladder
step below you, or you could go down. If a
photon comes by just that right energy level, it has
exactly the energy that's between you and that lower level,
then you're more likely to emit. You get pushed sort
(22:19):
of out of that energy level. And the reason is
that that photon changes the way the environment works. Right.
Photons are electromagnetic waves, so it creates a little electromagnetic
field there that makes what you were doing a little
less stable, so sort of pushes you out of that
state down to a lower state, and you end up
emitting another photon. So the bottom line is if you're
(22:41):
capable of emitting that photon, and one photon just like
that comes by, then you're gonna give it up and
emit that photon. And that's why it's called stimulated emission. Right, Like,
if you're an excited atom, you could just spontaneously have
your electron drop and admit a photon. That's called spontaneous emission. Yeah,
But stimulated emission is when you're excited and you get
(23:03):
hit by another photon and that causes you to drop
a level and emit another photon. Yeah. It's sort of
like peer pressure and you're like, hey, everybody's emitting that
red photon. I got one, I could emit one, and yeah,
yeah I could, and so I will. This is the
right time, you know. And so that's what the stimulated
part is. Right, Um, it's not. This is not nocturnal emissions.
(23:25):
People were talking about photons stimulating electrons into a emitting
war photons. What's the acronym for that one? Leaner? Um?
So to review, right, you start, you get some material,
you gotta pump it with energy. It's not free energy, right,
(23:46):
you gotta pump it with energy somehow. You gotta get
the atoms excited in your media and lock of stuff. Yeah,
it's like you know your comedy routine. You need somebody
go out there and warm up the crowd. Right, So
first you warm up the crowd, you get it's called
population inversion. Maybe've heard that phrase by everyone a beer,
that's right, We've discovered alcohol makes people laugh at the
(24:08):
jokes more. And so the physics equivalent for lasers, right,
is you pump the room with with energy and you
get all those electrons up at that level, and then
one of them will one of them will pop, right,
and that will cause the chain reaction. Having one photon
around will make all these other atoms which you know
(24:28):
are holding that photon inside them. Basically, birds didn't get
rid of it. They'll start emitting and then and then
more and more will admit. But they have to get
hit by a photon for them to release a photon, right, Like,
it doesn't just yeah, it's not because your neighbor shot
out a photon, then you shoot out a photon. It's
like you got you have to get hit by a
photon for you to get stimulated. Yeah, you don't have
(24:50):
to absorb it, but having the photon nearby close enough
to interact with the atom will change the electromagnetic vicinity
essentially and cause it to do that. And that's why
you usually you also put this block of atoms in
a resonant cavity. Basically you put two mirrors on either
side so that you capture the photons and you sort
of bounce them around inside. It's the same reason why
(25:10):
you have like walls in your oven, right, you want
to reflect the energy back so that it builds on itself. Right.
But that that whole process I heard is still even
a mystery for physicists, Like why exactly does the stimulated
atom shootout a photon that's exactly exactly like the one
that just went by closely or that hit it. Why
(25:31):
does it create a photon that's exactly identical to the
one that it saw with the same like wiggle and
the same timing in this exact same direction. That's still
kind of a mystery, right. Well, I think there's some
quantum mechanical arguments that that suggested. I think there's a
lot of the details are not perfectly understood. But you know,
the photon creates destabilizes the atom a tiny bit, right,
(25:55):
and so we can understand that there's something called firms
Golden rule, which tells us about how how things like
to decay, and so having that photon around definitely helps
us understand how the electron would be more likely to
jump down. Um. But yeah, why why it comes out
in exactly the same phase for example, I think it's
more likely too, but not guaranteed. So I think there
(26:16):
definitely are some some open questions there before we keep going,
Let's take a short break. Okay, So that's the S
(26:36):
E N L A S E R and so we
we tried. We covered all the letters. So it's light
amplified by stimulated emission radiation, that's right, and um. And
so you have it in this box and you have
these residents. You have a resident cavity. You have either mirrors, right,
bounce it back and forth, so the photons you emit
more photons to emit and um. You know, you can
(26:57):
have a little hole in the side so that some
of them leak out, and that's basically your laser. That's
how you produce it, right. But it can be a
constant thing. You can be constantly pumping it with energy,
pushing the electrons up and then they come down. You
get photon, you push them back up right so it
can be a continual thing. Um. One of the most
interesting lasers I ever saw was actually here on on
campus at U SEE. I as a professor here Franklin
(27:19):
Dollar who does fusion research, and they're trying to create
fusion by focusing a bunch of lasers all in the
same place. And he had this amazing setup where had
a bunch of lasers all overlapping in his lab and
he created a ball of plasma that was just floating
there in empty space. It was incredible. You can trap
atoms with lasers basically, right, you can do that, but
(27:42):
here he was just basically heating the air with a
bunch of lasers. By pointing a bunch of lasers so
they overlapped in one place in space. He heated up
the air hot enough to ionize and create a floating
ball of plasma. It was like looking at stable lightning.
It was pretty incredible. But these are These mirrors are
pretty cool because they're not just any mirrors that you
put on both sides of your stimulated stuff. It's like
(28:06):
one of them has to be a one way mirror.
One of them is a regular mirror, but the other
one is like a half mirror, meaning that it reflects
some of the light, but it also lets through some
of the light. Right, that's right. If both of them
were perfect mirrors, then you would never get anything out
of your laser. You just they would all stay inside
the cavity. So you have to have one of them
being imperfect mirrors that some of them leak out. Yeah,
(28:27):
So that that's kind of where the laser is. It's
kind of like a light echo chamber. Meaning you get
you get all your atoms excited, and then you set
one one of them off and then that will, for example,
go to the right, bounce off the mirror, go to
the left, hit another atom, cause it to also admit
(28:48):
an exact copy of that photon hit the other mirror.
Then both of them come back to the stuff, and
then they stimulate two other atoms, and then that creates
four photons and that just kind of builds and multiplies
within your echo chamber. But because one of the mirrors
is one way or semi transparent, that's where the laser
shoots out. Right, Yeah, yeah, exactly. Did I just make
(29:08):
that up? You should be the physicist on this podcast, man,
But I mean that's that's an important part of it. Right.
It's like you have you want to develop an echo chamber,
but you have to let some of the light out,
that's right. Yeah, If you don't let some of that out,
then it's pretty quickly going to get overheated. You're gonna
laser your own laser, right, And it's for all those
(29:31):
for all of us who have ever built a death star.
You know that you want it to blow up your
enemies basis, you don't want it to destroy your own.
But then it's stimulating the stuff in between. You can
do that several ways. Like your stuff can be a
gas or it can be crystal to right, that's right.
(29:54):
And if you want a laser to give you light
of a certain wavelength, like you want a red laser
or a green laser, or an X ray laser or something,
you have to find a material that has steps in
the ladder, their steps in their electron ladder that are
just the right size. Right. You can't just tune it
up to anything you want, right, You can't say I
(30:15):
want photons of this frequency. You have to find some
material that has electrons um that have an energy level
that has just the right size and that's why some
of these things are easy, and some of these things
are hard, like X ray lasers are really difficult to build,
and they're really everywhere, right, Like I was thinking, like
if you have a mouse in your computer and it's
(30:36):
an optical mouse that has a little laser in it, right,
that's right, Yeah, yeah, lasers are everywhere, and uh, it's
amazing how influential they have become. You know. And if
you look back at the history of the lasers, not
only is it a big mess nobody can agree about
who invented them, but in the early days there was
a lot of skepticism that it was even useful at all. Right,
(30:57):
some scientists thought it was impossible to make a laser, right, Yeah,
it was Neil's bore. He tried to make an argument
using the Heisenberg and certainty principle. He was like, you
can't have that many atoms in a specified state. He
thought it would just be impossibly that quantum mechanics would
make it not possible to make a laser, when in fact,
you need quantum mechanics to build a laser. Right, So
(31:17):
it works the other direction, So sometimes famous scientists get
it wrong. What was his argument for saying that it
was impossible, Well, you know, the Heisenberg and certainty principle
tells you that there's a certain there's a limit to
how much information you can have, right, And so he
was arguing that having all these atoms in the same state,
that you're specifying their energy um too tightly, right, you
(31:40):
can't the same way the Heisenberger and certainty principle tells
you that you can't know the position and momentum um
of a particle at the same time. It also applies
to the energy and timing information, and so a laser
is trying to isolate a bunch of particles have the
same energy all at the same time. And so he
thought that that was going to violate the Heisenberg on
(32:01):
certainly principle. But clearly it doesn't. We shot that down
with a laser's right, with our fully operational battle station.
So so there's, uh, it's interesting that there are all
kinds of different kinds of laser right, Right, Like your
mouse can have a laser on it, but you can
also use a laser to cut through steel, right, Like,
(32:23):
what's the difference between the laser and my mouse and
the laser that can cut through things nothing, you're a mouse.
Laser can cut through steel, horrey, you just never tried. Know.
The difference is just the intensity, right, the number of
photons per second. Photons have energy, and when something is
hit by a laser, they deposit their energy into whatever
is hit by it. If it's not a very bright laser,
(32:45):
then you're not I don't have a whole lot of
photons per second, then you're not depositing a lot of energy, right.
So that's why you can shine you know, a simple
laser pointer and as your skin and it doesn't burn, right,
But if you had ten thousand laser point and you
hit them all at the same place in your skin,
that would be the same as having one really powerful laser,
and yeah, you could cut a hole in yourself. So
(33:07):
cutting lasers are just lasers with a higher intensity UM
and they can have more photons per second and they
do that. How do you create more intensity? Do you
just pump the material more or do you do you
know what I mean? Like, what's the difference. If I
had the same material, how do I get more laser
out of it? Yeah, you can pump the material more,
you can have more material. Um you're gonna have you
(33:28):
must be must also have to do with how you
tune the one wayness of your one way mirror how much,
And that's that's some fracture of the energy out per second.
So there's probably lots of ways to do it. Well.
Lasers are everywhere in our lives. But I heard somebody
once told me that the biggest impact lasers have had
is in science, helping us make instruments to measure things
(33:50):
so that we can expand our knowledge about the universe. Um. Yeah,
lasers everywhere. Um, but I thought you were going to
say something about like laser lithography, like we can all
design our own cutting board logos and have lasers burn
them out. Yeah. No, the maker, the maker movement is
(34:12):
very grateful for lasers, but in the sense that you know,
like that's how we know for example, or initially that's
how we kind of figured out that the gravitational waves
measurement that depends on lasers, right, absolutely. Yeah. That uses
two lasers um in two different directions, and then you
shoot them away and they bounce back and use that
as a way to measure the distance. You count the
(34:32):
number of wiggles the laser has had. Yeah, Yeah, and
that's how they do a lot of like DNA studies,
and you can use lasers to figure out what materials
are made out of. So it's kind of in scientific
instrumentation has been a huge Lasers have had had a
huge impact, not just in like consumer products and death
(34:54):
rays that were never made, it's in science, right, it's
in its Lasers have really kind of boosted and amplified
what science can do. And that's right. Yeah, we're all
emitting more papers thanks to lasers. We're stimulated to emit
more papers. Yeah. Lasers also play a big role in
fusion research, as we were mentioning earlier. Um, you know
it's a powerful device, right, you have you have light
(35:16):
with a specific wavelength. You can focus at a very
specific spot and so it uh, and that's what scientists do,
you know, They think, how can I answer this question
with the tools I have? And that's a very specific tool.
It's like a tiny little science scalpel, right, and that
lets you sometimes cut problems open that you otherwise couldn't. Yeah.
So the next time you are at the grocery store
(35:37):
and are checking out and you hear that people, that's
a that's a laser at work. There there's a little
tiny death ray death ray to scan your your bananas.
That's right, you're fully operational grocery store uses lasers. Yeah,
all right. Well, I hope this discussion stimulated you and
(36:00):
made you focus with laser pocisition. And if you have
any questions, you can admit them to us. We'd love
to hear him see you next time. If you still
have a question after listening to all these explanations, please
drop us a line. We'd love to hear from you.
(36:22):
You can find us at Facebook, Twitter, and Instagram at
Daniel and Jorge that's one word, or email us at
Feedback at Daniel and Jorge dot com.
Hey, Daniel, let's talk about acronyms. Acronyms are actually a
really really important part of science. Whenever you have a
good idea, you have to come up with an acronym
or it's not going to be catchy. Well, I heard
there have been some pretty unfortunate acronyms in the history
of science. There are I googled for worst acronyms ever,
and I came up with some that you gotta wonder,
(00:27):
like people must have known what was going on, you know. So, um,
one of my favorites is Phase one Observing Proposal System.
So for those of you filing along at home, that's
p O O P S. So yeah, you can put
that together yourself. But but I heard that one day
actually grabbed the y from system, like they consciously made
(00:51):
the choice not to be called poops but to be
called poop. See, well, there is one acronym that's a
famous acronym for a physics topic. But I think we
think maybe most people don't even know it's an acronym. Yeah,
And maybe that means it's really successful, right, because it's
become a word in its own right. You know, people
actually use the word yeah, and that word is laser
(01:14):
camp to do. So, do you know what it stands for? Horror? Hey,
don't look it up. Do you know what it stands for?
Test NERD CREB test, I do it. It stands for
UM light amplification through stimulated emission radiation. Being we have
a winner, folks, give him a laser. But I heard
(01:35):
that the acron could have been different. It could have
been light oscillation by stimulated emission radiation. That's right, And
I don't think that one would have caught on quite
as well. That would be l o s E er
has some obvious disadvantages. You don't want to be a
loser scientist. That would be That would be obvious him
(02:14):
and I'm Daniel, and welcome to our podcast Daniel and
Jorge Explain the Universe, in which we talk about all
kinds of cool things about the universe. Yeah, and we
take the universe apart, we disassemble its acronyms, and we
tell you what it actually means. All the cool things
you see in science fiction movies, books, laser guns, stuff
like that. We break it down and make sense of
(02:35):
it for you. So, if you have ideas for what
you'd like us to talk about, send them into feedback
at Daniel and Jorge dot com. We love hearing your
topic suggestions. Today on the program, we're going to be
talking about lasers, lasers. How does a laser work? What
(02:57):
is a laser? Who came up with a laser? Where
can I at my laser death ray? These are important questions.
How can I make it my living to laz about?
Here a cartoonist, you're already laser by which I mean
you are brilliant and cutting. That's right, and very um focused,
(03:18):
very focused exactly. So, Yeah, lasers are. Lasers are awesome.
Everyone knows what a laser is. My kids know what
lasers are. Yeah, I mean they're they're in science fiction everywhere. Um,
people have laser pens, right, lasers there. You probably have
dozens of lasers in your house, right, Lasers used for everything? Yeah,
they're in our everyday lives. Like every time you go
(03:41):
buy something at a store. Assume you still go to
physical store. But if they scan your product in they're
using a laser, that's right. And if you still have
a CD player, that thing is read by a laser.
A CD what you're too young to understand those things?
For he For those of you under forty we used
to store music on these shiny little disks. Yeah, they'd
(04:02):
use lasers. So they were literally everywhere. I mean, there
are optical drives, right, anything that reads the disc. So
if you pop in a disk to your PlayStation, that's
using a laser in there, that's right. And lasers have
an enormous variety of applications, you know, from tiny laser
pointers to world size lasers that people are experimenting with
to try to deflect asteroids that might blow up the Earth. Yeah,
(04:26):
like in the Dead Star and in Star Wars, right,
that's right. Those that's the fiction, of course, But the
group building a laser to disflect asteroids, that's real. They
might save the planet. They might save the planet exactly.
So lasers are everywhere. They're definitely an important part of
our culture and of our technology and of everything you do.
(04:47):
But the question we had was how do they do
what they do? What does it mean to lazy? How
do you build a laser? Could you assemble one from
the stuff in your kitchen? Yeah? Can you shoot it
in the movies like to destroy other specihopes? That's right?
Do they really make the pew pew pew sound. That's
that's the question. I want to know the answer to
what sound does a laser make? Is it like pure
(05:09):
or it's definitely one of those? How good? I hit
it on my first three talk tries. But we were
wondering how many people out there know what a laser
is and how it works. I walked around on campus
and I asked people, do you know how a laser works?
Does of you listening think about it for a second.
(05:31):
Here's what people had to say, mate, Sorry, uh, focused light,
light gets multiplied and focused? Okay, cool light? All right.
I guess not a lot of deep knowledge about lasers
out there. I had the impression people think lasers are
(05:52):
like you have a light bulb and then maybe you
have a lens to focus it, and that's your laser.
I like the person who said, how did how do
lasers work? By light? Technically? You're right, you can go
wrong with that answer. That's right. Yeah, go with a
very very general answer, how does this work? Physics? Right?
You could just say physics to any question to ask people? Really,
(06:12):
even math? Can I say how does math work? No?
But that's not a topic for our podcast, right because
math is outside the universe. Beyond the scope of this podcast.
That's right. But maybe it's the only thing more fundamental
in physics is math. Maybe. I like how you say, maybe,
is there is there anything else? Maybe philosophy. I guess
(06:34):
philosophy and math, you know, down there at the at
the down in the dirt and the roots of human
intellectual exploration. Yeah, so lasers are pretty interesting, right, They
have an interesting history, Like apparently historians don't really know
who invented the laser, or they haven't settled on who
(06:55):
invented laser. That's right. And I heard that one really
important science historian actually wrote a him about it once.
Oh really is that true? Yeah? His name is Um.
Hold on, I have it here. Let me check Jorge him.
Oh yeah, that comic laureate of the Internet. Should we um?
Should we read the poem? Sure? Go for it. I'm
(07:17):
not sure if this is supposed to be set to
music or rhyme. Yeah, it's supposed to be said to
laser music. So you think, think eighties here and then
go for it. Um. So, I wrote this when the
laser turned fifty about eight years ago, was the anniversary
(07:37):
of the laser. I'll read it and you make the
pu pu sounds all right. The laser turns fifty this week,
an important event in history. But who developed this amazing
technique that's still kind of a mystery. Was it Ted
my mom who built the first laser? Or was it
Towns in Shacklow who wrote the seminal paper and it
(07:58):
goes on like that role beautifully crafted versus oh thanks,
Yeah it was you know what happened? I was in
Ottawa and I went to visit they have a laser
institute at one of the university there, and they explained
to me that the anniversary of the laser was coming up,
and so they explained to me how the laser works.
And in fact, I think that's kind of related to
(08:19):
how you and I started working together, right, Yeah, you
just reminded me of this today. Apparently your comic about
the laser is one of the ones that I read
and uh and induced me to write you an email.
So yeah, the history is kind of funny because the
Nobel Prize for the laser, the first prototype for the laser,
and the first paper about the laser are all credited
(08:42):
to different people, Like, nobody knows who invented this really, yeah,
it might have been one of these things where like
an idea that whose time has just come, you know,
we're on the cusp is sort of the next thing
to happen, and a few people contribute bits and pieces here,
and some other person puts these things together first there,
and uh, it's a bit of a mess. Yeah, it's
a bit of a mess. I think it's fascinating. Also
(09:03):
how important it is to assign credit for things like
we have the laser. It's awesome. Are people just fighting
about the money, like who earns a penny every time
they make a laser pointer? Or is it about like
the credit and scientific history? You know, it's it's interesting
to me how how long and nasty this battle is.
You mean you wouldn't fight to have that in your tombstone?
(09:24):
Daniel Whiteson invented the laser? Who would? Oh, I'm definitely
putting that on my tombstone. True or not? I mean,
you can put anything you wanted your trimstone. Nobody fact
checks tombstones. It's like fake news applied to tombstones. I'm
taking credit for all sorts of stuff in my tombstone. Well,
let's get into what Daniel is a laser? Right? So
(09:48):
a laser is different from a flashlight, right, It's not
just a flashlight with a lens, Okay. A laser is
something that produces a bunch of light, usually of the
same color or so, like all a bunch of photons
of the same energy, and they should all be going
in the same direction, right, So they're perfectly parallel. Meaning
(10:09):
if they're like, you know, a tiny distance apart now,
then a hundred meters away or a kilometer away, or
a million miles away, they'll still be the same distance apart,
perfectly parallel, perfectly parallel photons, right, yeah, exactly, So photons
usually of the same color, shot perfectly parallel, and also
(10:29):
wiggling the same way. Right. Remember, the photons are waves,
and they're like all other particles. They're governed by their
wave equation, and waves wiggle, right, they go up and
they go down, they go up and they go down.
And if you have two waves, if they're wiggling in
opposite directions, one wiggles up the other one wiggles down,
then they can cancel each other out. Right, So we
(10:49):
want our photons all wiggling the same way, so they
all sort of pushed together. It's like folks, on a
boat rowing at the same time. They all push together
for constructive interference to make a strong when they hit
something at the end. You want them to be perfectly synchronized.
Otherwise they might cancel each other out when they hit something. Yeah,
that's right, or they might you know, cancel each other
(11:10):
out part of the way. Um. You know these things,
these interference effects depend on the phase, and so yeah,
you want them all pushing in the same direction, um
at the same time. And so that's what a laser produces. Right.
That's that's what it means to be a laser. And
that's an important distinction of people to understand. That's not
just like a powerful flashlight or of uh flashlights somebody
put a lens in front of. It's a It's really
(11:31):
a very different kind of source of light. It's not
just a really bright light. It's like a perfectly ordered,
perfectly parallel beams of light. That's right. And there's two
kinds of lasers. One kind is the kind we're talking
about where all the photons have the same color, so
it's monochromatic, right, it's a single color of light, all
the photons of the same energy, the same color. UM.
That's the kind that you make to produce beams. You
(11:53):
can also produce laser pulses, right. These are short bursts,
and those require having lots of different colors so that
you add they add up and cancel out in just
the right way to have a localized burst. And you
can add up all the different wiggles together to make
the burst of any shape you want, right. And that's
different than a flashlight, because a flashlight it's just pumping
(12:15):
out photons with all kinds of colors and all kinds
of phases, and they're all out of sync with each other,
all these photons, that's right. And also they go in
in all different directions, right. Um, a flashlight usually has
like a tungsten filament bulb or something, right, and that's
just glowing and it's sending light in every direction. And
even if you have it, you know, coming out of
(12:35):
the front, so it's a little bit um shaped. You know.
You can take, for example, a flashlight and you can
point it at the moon, right, and as as you
get further away from the source of the light, the
size of the beam grows. Right. Flashlight makes a cone,
and the cone grows with distance, So you can point
it to the Moon, and you basically cover the whole
Moon with your flashlight, because by the time you get
(12:57):
to the distance of the Moon, the cone is huge.
Even if you focus it with like a lens and
try to get them parallel, they won't be perfectly parallel
exactly right. There's always going to be some spread there.
Whereas with a laser. If you take a laser and
you point it at the moon, if you if it's
a good laser, when it gets there, should have the
beam should have the same with is when is when
it left. So that's how that's why lasers are powerful, right,
(13:22):
because with just a few photons they can go a
great distance together and so they can transmit that information.
But they're also kind of in sync so they can
deliver all that power when they get there. That's right.
And that example about a laser to the Moon is
not just like a made up example. I don't know
if you know, but the astronauts who visited the Moon
left mirrors on the surface of the Moon so that
(13:44):
we can bounce lasers off of them and use that
to measure the distance from the Earth to the Moon.
I think that's pretty cool. The Earth's beak is selfie.
You can think we can take a selfie by shooting
the laser at the moon. And that's right. Even though
this is decades before the concept of selfies, it was
it was prescient that way, right. They were forward, forward looking.
(14:06):
NASA is always looking into the future. NASA invented the selfie.
We just we just give credit. We just give credit
to them. They can put it on the Actually the first,
the first selfie comes from decades and decades before that.
But but yeah, the first astronomical selfie for sure, first
laser selfie, that's right. Okay, So that's what the laser is.
(14:31):
It's like, it's like something that makes light, that shoots
light that's perfectly in sync and perfectly parallel and that's
really powerful. Okay, so what why is it called laser?
Like what what? What does that acronym mean? Light amplified
by stimulated emission radiation. That's right, let's break that down, right.
The first one is just light. Okay, so photons are light,
(14:52):
that's obvious. The last one, the last one is radiation, right,
and radiation in this case also it just means light. Yeah.
I think that's because they didn't want to call it
a laser that would have been more awkward with an
l So both of those words light and radiation just
(15:16):
refer to the photons, right, Okay. So it's something that
makes light, something that makes light and um and it
makes it in this special way using this process called
stimulated emission. Okay. And that's the really the guts of
the laser. That's what's going on inside, is that it's
a system that creates this stimulated emission. So we should
dig into that. The A and laser beings amplified, meaning
(15:39):
you're not just making that use sort of amplifying it somehow.
That's right. The basic principle of the laser is you
start with one photon of the color that you want,
you know, and you amplify use that to use this
system to multiply you. So I want to start with
one photon and then you create a chain reaction that
gives you ten photons, and then a hundred photons, and
then a thousand photons, etcetera, etcetera. Grows exponentially until you
(16:01):
have a very very intense beam of photons all the
same kind. And the key is the stimulated emission. That's
the thing that basically copies the photon. It says, if
you have one of the right wavelength or to all
the right attributes, then I can make more for you.
That's this process called stimulated emission. Okay, let's get stimulated
by stimulated emission. But first let's take a quick break. Okay,
(16:36):
So laser is something that makes light that's all the
same color, the same wavelength, the same direction, the same wiggle,
and it's all done by something called stimulated emission. What
does that mean? Right? So the thing that's doing the
emission is just an atom, and so you have some
medium in your laser. Maybe it's a crystal, maybe it's
(16:57):
a gas that doesn't really matter, but it's a bunch
of atoms. And atoms can emit light, right, any atom,
any atom can emit light. Right, you make you get
things hot and they glow, right, that's something emitting light.
So if you pump energy into some material, right, it
will absorb that energy and bring it internally into itself.
But then sometimes it gets rid of that energy. That's
(17:19):
called emission, and it turns that energy into light. And
the way that it does that is it has inside
it, it it has these electrons. Right, So every atom has
electrons whizzing around it, and there's electrons have a few
certain orbits that they can use around the atom. It's
like a bunch of different energy levels. Electrons can't just
have any random energy level around it atom. Based on
(17:41):
the shape of the atom and the configuration of the protons, etcetera.
There's a few places the electrons are allowed to live,
so they're called energy levels. And you can imagine sort
of a ladder of these energy levels. And that's kind
of related to their wave nature of electrons, right, because
their waves they can only fit in so many ways
around the atom. Right, It's sort of related to that, right,
(18:03):
It's very closely related. Yeah. Um, the reason that there
are discrete energy levels, right, quantized energy levels, is precisely
because of those waves and the way the waves fit
together around the atom. So a simple way to think
about it is when the electron goes around the atom,
it's going to do it's wiggling, and you wanted to
build on itself. You don't want it to cancel itself out,
(18:23):
and so when it comes around one orbit, you need
to be in the same place in its wiggle either
it's wiggling up or it's wiggling down. It has to
fit a very specific number of wiggles in an orbit.
You can just do like three and a half that's right.
It has to wiggle once or twice or three times. Right.
If it wiggles one and a half times, then it's
(18:45):
going to get out of sync with itself and eventually
cancel itself out. So those are not stable solutions. So
you can't have an electron hanging out and wiggling one
and a half times around the atom. So each of
those is a different level. It's not like the Earth
going around the Sun, like if something moves as a
little bit, our orbit will increase a little bit. That's
not how electrons work. They have very specific orbits that
(19:06):
can fit around the nucleus of the atom. Yeah, that's
actually a really interesting deep question. Is the Earth's orbit quantized?
Are there an infinite number of orbits? That's not a
one with a simple answer. If gravity is not quantum mechanical,
then you're right, so there's an infinite number of orbits
the Earth can take. However, if the gravity is quantized,
(19:27):
then then you're wrong, and there are energy levels around
the Sun, but those energy levels would be so tiny
we could probably not even see them anyway. That might
be the subject of a different podcast. Yeah, exactly. Yeah.
So the energy, So the electron has these energy levels
it has on these ladder. This ladder can go up
and it can go down. Yeah, people use the ladder analogy, right,
(19:47):
like electrons can be here or it can go up
a level or another level. Right, It's like very discrete steps.
And just like with the ladder, what happens when you
go up a level? Will you It takes some energy
to do that, right, put some energy into your thigh
muscle to push you up, and then you're storing more
energy or you have more gravitational energy because you're higher up.
The same thing happens with the electron. How does it
(20:09):
go up a level? It needs to get energy from somewhere, right,
it needs to get heated up or absorb some light
or something. So it can go up a level, right,
and then it can go down a level. And what
happens when it goes down a level While the energy
level it was at is fixed and the energy level
is going to is fixed, so the energy difference between
them is fixed, meaning every atom has the same levels.
(20:31):
And if electrons jumped down from one level to the
lower one. Then they're going to release a photon whose
energy is exactly the difference between those two levels, right,
conservation of energy. The electron loses energy, goes down a level,
and it gives off that missing that extra energy in
terms of a photon. Okay, so the electron goes down
a level, it will shoot out a photon with that
(20:53):
energy that it doesn't need anymore. That's right, exactly. So
how do you get a bunch of photons of all
the same color in the same direction. When you get
a bunch of atoms, You get them all to have
their electrons up one level, right, You heat them up,
you pump some energy into them somehow, and then you
get them to come down all about the same time.
You get them excited. You get him excited, right, and
(21:14):
then you get them the big let down. Yeah, all,
And when they get the let down, that's when they
give off a photon, and each one will give off
the same color photon. The photon is determined exactly by
its energy, which is determined by its wavelength. Right, those
things things are all connected, right, But they don't all
(21:35):
in a laser. They don't all give them out at
the same time, it's it's kind of like how you
said earlier. You want to cause a chain reaction that
will make all the atoms in your laser shoot all
these photons perfectly saying exactly so that chain reaction is key,
and you can have an atom and you can give
it energy. So the electron goes up one level and
then it's happened to just hang out there for a while, right,
(21:57):
But what happens when another photon just the right energy
level comes by, Like if you're an electron, you're an
excited state, um, and there's like a ladders step ladder
step below you, or you could go down. If a
photon comes by just that right energy level, it has
exactly the energy that's between you and that lower level,
then you're more likely to emit. You get pushed sort
(22:19):
of out of that energy level. And the reason is
that that photon changes the way the environment works. Right.
Photons are electromagnetic waves, so it creates a little electromagnetic
field there that makes what you were doing a little
less stable, so sort of pushes you out of that
state down to a lower state, and you end up
emitting another photon. So the bottom line is if you're
(22:41):
capable of emitting that photon, and one photon just like
that comes by, then you're gonna give it up and
emit that photon. And that's why it's called stimulated emission. Right, Like,
if you're an excited atom, you could just spontaneously have
your electron drop and admit a photon. That's called spontaneous emission. Yeah,
But stimulated emission is when you're excited and you get
(23:03):
hit by another photon and that causes you to drop
a level and emit another photon. Yeah. It's sort of
like peer pressure and you're like, hey, everybody's emitting that
red photon. I got one, I could emit one, and yeah,
yeah I could, and so I will. This is the
right time, you know. And so that's what the stimulated
part is. Right, Um, it's not. This is not nocturnal emissions.
(23:25):
People were talking about photons stimulating electrons into a emitting
war photons. What's the acronym for that one? Leaner? Um?
So to review, right, you start, you get some material,
you gotta pump it with energy. It's not free energy, right,
(23:46):
you gotta pump it with energy somehow. You gotta get
the atoms excited in your media and lock of stuff. Yeah,
it's like you know your comedy routine. You need somebody
go out there and warm up the crowd. Right, So
first you warm up the crowd, you get it's called
population inversion. Maybe've heard that phrase by everyone a beer,
that's right, We've discovered alcohol makes people laugh at the
(24:08):
jokes more. And so the physics equivalent for lasers, right,
is you pump the room with with energy and you
get all those electrons up at that level, and then
one of them will one of them will pop, right,
and that will cause the chain reaction. Having one photon
around will make all these other atoms which you know
(24:28):
are holding that photon inside them. Basically, birds didn't get
rid of it. They'll start emitting and then and then
more and more will admit. But they have to get
hit by a photon for them to release a photon, right, Like,
it doesn't just yeah, it's not because your neighbor shot
out a photon, then you shoot out a photon. It's
like you got you have to get hit by a
photon for you to get stimulated. Yeah, you don't have
(24:50):
to absorb it, but having the photon nearby close enough
to interact with the atom will change the electromagnetic vicinity
essentially and cause it to do that. And that's why
you usually you also put this block of atoms in
a resonant cavity. Basically you put two mirrors on either
side so that you capture the photons and you sort
of bounce them around inside. It's the same reason why
(25:10):
you have like walls in your oven, right, you want
to reflect the energy back so that it builds on itself. Right.
But that that whole process I heard is still even
a mystery for physicists, Like why exactly does the stimulated
atom shootout a photon that's exactly exactly like the one
that just went by closely or that hit it. Why
(25:31):
does it create a photon that's exactly identical to the
one that it saw with the same like wiggle and
the same timing in this exact same direction. That's still
kind of a mystery, right. Well, I think there's some
quantum mechanical arguments that that suggested. I think there's a
lot of the details are not perfectly understood. But you know,
the photon creates destabilizes the atom a tiny bit, right,
(25:55):
and so we can understand that there's something called firms
Golden rule, which tells us about how how things like
to decay, and so having that photon around definitely helps
us understand how the electron would be more likely to
jump down. Um. But yeah, why why it comes out
in exactly the same phase for example, I think it's
more likely too, but not guaranteed. So I think there
(26:16):
definitely are some some open questions there before we keep going,
Let's take a short break. Okay, So that's the S
(26:36):
E N L A S E R and so we
we tried. We covered all the letters. So it's light
amplified by stimulated emission radiation, that's right, and um. And
so you have it in this box and you have
these residents. You have a resident cavity. You have either mirrors, right,
bounce it back and forth, so the photons you emit
more photons to emit and um. You know, you can
(26:57):
have a little hole in the side so that some
of them leak out, and that's basically your laser. That's
how you produce it, right. But it can be a
constant thing. You can be constantly pumping it with energy,
pushing the electrons up and then they come down. You
get photon, you push them back up right so it
can be a continual thing. Um. One of the most
interesting lasers I ever saw was actually here on on
campus at U SEE. I as a professor here Franklin
(27:19):
Dollar who does fusion research, and they're trying to create
fusion by focusing a bunch of lasers all in the
same place. And he had this amazing setup where had
a bunch of lasers all overlapping in his lab and
he created a ball of plasma that was just floating
there in empty space. It was incredible. You can trap
atoms with lasers basically, right, you can do that, but
(27:42):
here he was just basically heating the air with a
bunch of lasers. By pointing a bunch of lasers so
they overlapped in one place in space. He heated up
the air hot enough to ionize and create a floating
ball of plasma. It was like looking at stable lightning.
It was pretty incredible. But these are These mirrors are
pretty cool because they're not just any mirrors that you
put on both sides of your stimulated stuff. It's like
(28:06):
one of them has to be a one way mirror.
One of them is a regular mirror, but the other
one is like a half mirror, meaning that it reflects
some of the light, but it also lets through some
of the light. Right, that's right. If both of them
were perfect mirrors, then you would never get anything out
of your laser. You just they would all stay inside
the cavity. So you have to have one of them
being imperfect mirrors that some of them leak out. Yeah,
(28:27):
So that that's kind of where the laser is. It's
kind of like a light echo chamber. Meaning you get
you get all your atoms excited, and then you set
one one of them off and then that will, for example,
go to the right, bounce off the mirror, go to
the left, hit another atom, cause it to also admit
(28:48):
an exact copy of that photon hit the other mirror.
Then both of them come back to the stuff, and
then they stimulate two other atoms, and then that creates
four photons and that just kind of builds and multiplies
within your echo chamber. But because one of the mirrors
is one way or semi transparent, that's where the laser
shoots out. Right, Yeah, yeah, exactly. Did I just make
(29:08):
that up? You should be the physicist on this podcast, man,
But I mean that's that's an important part of it. Right.
It's like you have you want to develop an echo chamber,
but you have to let some of the light out,
that's right. Yeah, If you don't let some of that out,
then it's pretty quickly going to get overheated. You're gonna
laser your own laser, right, And it's for all those
(29:31):
for all of us who have ever built a death star.
You know that you want it to blow up your
enemies basis, you don't want it to destroy your own.
But then it's stimulating the stuff in between. You can
do that several ways. Like your stuff can be a
gas or it can be crystal to right, that's right.
(29:54):
And if you want a laser to give you light
of a certain wavelength, like you want a red laser
or a green laser, or an X ray laser or something,
you have to find a material that has steps in
the ladder, their steps in their electron ladder that are
just the right size. Right. You can't just tune it
up to anything you want, right, You can't say I
(30:15):
want photons of this frequency. You have to find some
material that has electrons um that have an energy level
that has just the right size and that's why some
of these things are easy, and some of these things
are hard, like X ray lasers are really difficult to build,
and they're really everywhere, right, Like I was thinking, like
if you have a mouse in your computer and it's
(30:36):
an optical mouse that has a little laser in it, right,
that's right, Yeah, yeah, lasers are everywhere, and uh, it's
amazing how influential they have become. You know. And if
you look back at the history of the lasers, not
only is it a big mess nobody can agree about
who invented them, but in the early days there was
a lot of skepticism that it was even useful at all. Right,
(30:57):
some scientists thought it was impossible to make a laser, right, Yeah,
it was Neil's bore. He tried to make an argument
using the Heisenberg and certainty principle. He was like, you
can't have that many atoms in a specified state. He
thought it would just be impossibly that quantum mechanics would
make it not possible to make a laser, when in fact,
you need quantum mechanics to build a laser. Right, So
(31:17):
it works the other direction, So sometimes famous scientists get
it wrong. What was his argument for saying that it
was impossible, Well, you know, the Heisenberg and certainty principle
tells you that there's a certain there's a limit to
how much information you can have, right, And so he
was arguing that having all these atoms in the same state,
that you're specifying their energy um too tightly, right, you
(31:40):
can't the same way the Heisenberger and certainty principle tells
you that you can't know the position and momentum um
of a particle at the same time. It also applies
to the energy and timing information, and so a laser
is trying to isolate a bunch of particles have the
same energy all at the same time. And so he
thought that that was going to violate the Heisenberg on
(32:01):
certainly principle. But clearly it doesn't. We shot that down
with a laser's right, with our fully operational battle station.
So so there's, uh, it's interesting that there are all
kinds of different kinds of laser right, Right, Like your
mouse can have a laser on it, but you can
also use a laser to cut through steel, right, Like,
(32:23):
what's the difference between the laser and my mouse and
the laser that can cut through things nothing, you're a mouse.
Laser can cut through steel, horrey, you just never tried. Know.
The difference is just the intensity, right, the number of
photons per second. Photons have energy, and when something is
hit by a laser, they deposit their energy into whatever
is hit by it. If it's not a very bright laser,
(32:45):
then you're not I don't have a whole lot of
photons per second, then you're not depositing a lot of energy, right.
So that's why you can shine you know, a simple
laser pointer and as your skin and it doesn't burn, right,
But if you had ten thousand laser point and you
hit them all at the same place in your skin,
that would be the same as having one really powerful laser,
and yeah, you could cut a hole in yourself. So
(33:07):
cutting lasers are just lasers with a higher intensity UM
and they can have more photons per second and they
do that. How do you create more intensity? Do you
just pump the material more or do you do you
know what I mean? Like, what's the difference. If I
had the same material, how do I get more laser
out of it? Yeah, you can pump the material more,
you can have more material. Um you're gonna have you
(33:28):
must be must also have to do with how you
tune the one wayness of your one way mirror how much,
And that's that's some fracture of the energy out per second.
So there's probably lots of ways to do it. Well.
Lasers are everywhere in our lives. But I heard somebody
once told me that the biggest impact lasers have had
is in science, helping us make instruments to measure things
(33:50):
so that we can expand our knowledge about the universe. Um. Yeah,
lasers everywhere. Um, but I thought you were going to
say something about like laser lithography, like we can all
design our own cutting board logos and have lasers burn
them out. Yeah. No, the maker, the maker movement is
(34:12):
very grateful for lasers, but in the sense that you know,
like that's how we know for example, or initially that's
how we kind of figured out that the gravitational waves
measurement that depends on lasers, right, absolutely. Yeah. That uses
two lasers um in two different directions, and then you
shoot them away and they bounce back and use that
as a way to measure the distance. You count the
(34:32):
number of wiggles the laser has had. Yeah, Yeah, and
that's how they do a lot of like DNA studies,
and you can use lasers to figure out what materials
are made out of. So it's kind of in scientific
instrumentation has been a huge Lasers have had had a
huge impact, not just in like consumer products and death
(34:54):
rays that were never made, it's in science, right, it's
in its Lasers have really kind of boosted and amplified
what science can do. And that's right. Yeah, we're all
emitting more papers thanks to lasers. We're stimulated to emit
more papers. Yeah. Lasers also play a big role in
fusion research, as we were mentioning earlier. Um, you know
it's a powerful device, right, you have you have light
(35:16):
with a specific wavelength. You can focus at a very
specific spot and so it uh, and that's what scientists do,
you know, They think, how can I answer this question
with the tools I have? And that's a very specific tool.
It's like a tiny little science scalpel, right, and that
lets you sometimes cut problems open that you otherwise couldn't. Yeah.
So the next time you are at the grocery store
(35:37):
and are checking out and you hear that people, that's
a that's a laser at work. There there's a little
tiny death ray death ray to scan your your bananas.
That's right, you're fully operational grocery store uses lasers. Yeah,
all right. Well, I hope this discussion stimulated you and
(36:00):
made you focus with laser pocisition. And if you have
any questions, you can admit them to us. We'd love
to hear him see you next time. If you still
have a question after listening to all these explanations, please
drop us a line. We'd love to hear from you.
(36:22):
You can find us at Facebook, Twitter, and Instagram at
Daniel and Jorge that's one word, or email us at
Feedback at Daniel and Jorge dot com.
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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