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