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How Does A Laser Work? · Daniel and Kelly’s Extraordinary Universe

0:07
Speaker 1: Hey, Daniel, let's talk about acronyms. Acronyms are actually a
0:10
Speaker 1: really really important part of science. Whenever you have a
0:13
Speaker 1: good idea, you have to come up with an acronym
0:15
Speaker 1: or it's not going to be catchy. Well, I heard
0:17
Speaker 1: there have been some pretty unfortunate acronyms in the history
0:21
Speaker 1: of science. There are I googled for worst acronyms ever,
0:25
Speaker 1: and I came up with some that you gotta wonder,
0:27
Speaker 1: like people must have known what was going on, you know. So, um,
0:31
Speaker 1: one of my favorites is Phase one Observing Proposal System.
0:37
Speaker 1: So for those of you filing along at home, that's
0:40
Speaker 1: p O O P S. So yeah, you can put
0:43
Speaker 1: that together yourself. But but I heard that one day
0:47
Speaker 1: actually grabbed the y from system, like they consciously made
0:51
Speaker 1: the choice not to be called poops but to be
0:54
Speaker 1: called poop. See, well, there is one acronym that's a
0:58
Speaker 1: famous acronym for a physics topic. But I think we
1:02
Speaker 1: think maybe most people don't even know it's an acronym. Yeah,
1:05
Speaker 1: And maybe that means it's really successful, right, because it's
1:08
Speaker 1: become a word in its own right. You know, people
1:10
Speaker 1: actually use the word yeah, and that word is laser
1:14
Speaker 1: camp to do. So, do you know what it stands for? Horror? Hey,
1:18
Speaker 1: don't look it up. Do you know what it stands for?
1:20
Speaker 1: Test NERD CREB test, I do it. It stands for
1:25
Speaker 1: UM light amplification through stimulated emission radiation. Being we have
1:32
Speaker 1: a winner, folks, give him a laser. But I heard
1:35
Speaker 1: that the acron could have been different. It could have
1:37
Speaker 1: been light oscillation by stimulated emission radiation. That's right, And
1:42
Speaker 1: I don't think that one would have caught on quite
1:44
Speaker 1: as well. That would be l o s E er
1:47
Speaker 1: has some obvious disadvantages. You don't want to be a
1:50
Speaker 1: loser scientist. That would be That would be obvious him
2:14
Speaker 1: and I'm Daniel, and welcome to our podcast Daniel and
2:17
Speaker 1: Jorge Explain the Universe, in which we talk about all
2:21
Speaker 1: kinds of cool things about the universe. Yeah, and we
2:24
Speaker 1: take the universe apart, we disassemble its acronyms, and we
2:27
Speaker 1: tell you what it actually means. All the cool things
2:29
Speaker 1: you see in science fiction movies, books, laser guns, stuff
2:33
Speaker 1: like that. We break it down and make sense of
2:35
Speaker 1: it for you. So, if you have ideas for what
2:38
Speaker 1: you'd like us to talk about, send them into feedback
2:40
Speaker 1: at Daniel and Jorge dot com. We love hearing your
2:44
Speaker 1: topic suggestions. Today on the program, we're going to be
2:46
Speaker 1: talking about lasers, lasers. How does a laser work? What
2:57
Speaker 1: is a laser? Who came up with a laser? Where
2:59
Speaker 1: can I at my laser death ray? These are important questions.
3:02
Speaker 1: How can I make it my living to laz about?
3:06
Speaker 1: Here a cartoonist, you're already laser by which I mean
3:12
Speaker 1: you are brilliant and cutting. That's right, and very um focused,
3:18
Speaker 1: very focused exactly. So, Yeah, lasers are. Lasers are awesome.
3:24
Speaker 1: Everyone knows what a laser is. My kids know what
3:26
Speaker 1: lasers are. Yeah, I mean they're they're in science fiction everywhere. Um,
3:31
Speaker 1: people have laser pens, right, lasers there. You probably have
3:34
Speaker 1: dozens of lasers in your house, right, Lasers used for everything? Yeah,
3:38
Speaker 1: they're in our everyday lives. Like every time you go
3:41
Speaker 1: buy something at a store. Assume you still go to
3:43
Speaker 1: physical store. But if they scan your product in they're
3:47
Speaker 1: using a laser, that's right. And if you still have
3:50
Speaker 1: a CD player, that thing is read by a laser.
3:52
Speaker 1: A CD what you're too young to understand those things?
3:56
Speaker 1: For he For those of you under forty we used
3:59
Speaker 1: to store music on these shiny little disks. Yeah, they'd
4:02
Speaker 1: use lasers. So they were literally everywhere. I mean, there
4:06
Speaker 1: are optical drives, right, anything that reads the disc. So
4:09
Speaker 1: if you pop in a disk to your PlayStation, that's
4:12
Speaker 1: using a laser in there, that's right. And lasers have
4:14
Speaker 1: an enormous variety of applications, you know, from tiny laser
4:17
Speaker 1: pointers to world size lasers that people are experimenting with
4:22
Speaker 1: to try to deflect asteroids that might blow up the Earth. Yeah,
4:26
Speaker 1: like in the Dead Star and in Star Wars, right,
4:29
Speaker 1: that's right. Those that's the fiction, of course, But the
4:32
Speaker 1: group building a laser to disflect asteroids, that's real. They
4:36
Speaker 1: might save the planet. They might save the planet exactly.
4:39
Speaker 1: So lasers are everywhere. They're definitely an important part of
4:43
Speaker 1: our culture and of our technology and of everything you do.
4:47
Speaker 1: But the question we had was how do they do
4:49
Speaker 1: what they do? What does it mean to lazy? How
4:52
Speaker 1: do you build a laser? Could you assemble one from
4:55
Speaker 1: the stuff in your kitchen? Yeah? Can you shoot it
4:57
Speaker 1: in the movies like to destroy other specihopes? That's right?
5:00
Speaker 1: Do they really make the pew pew pew sound. That's
5:04
Speaker 1: that's the question. I want to know the answer to
5:07
Speaker 1: what sound does a laser make? Is it like pure
5:09
Speaker 1: or it's definitely one of those? How good? I hit
5:16
Speaker 1: it on my first three talk tries. But we were
5:20
Speaker 1: wondering how many people out there know what a laser
5:23
Speaker 1: is and how it works. I walked around on campus
5:26
Speaker 1: and I asked people, do you know how a laser works?
5:28
Speaker 1: Does of you listening think about it for a second.
5:31
Speaker 1: Here's what people had to say, mate, Sorry, uh, focused light,
5:39
Speaker 1: light gets multiplied and focused? Okay, cool light? All right.
5:46
Speaker 1: I guess not a lot of deep knowledge about lasers
5:49
Speaker 1: out there. I had the impression people think lasers are
5:52
Speaker 1: like you have a light bulb and then maybe you
5:54
Speaker 1: have a lens to focus it, and that's your laser.
5:57
Speaker 1: I like the person who said, how did how do
5:58
Speaker 1: lasers work? By light? Technically? You're right, you can go
6:03
Speaker 1: wrong with that answer. That's right. Yeah, go with a
6:06
Speaker 1: very very general answer, how does this work? Physics? Right?
6:09
Speaker 1: You could just say physics to any question to ask people? Really,
6:12
Speaker 1: even math? Can I say how does math work? No?
6:17
Speaker 1: But that's not a topic for our podcast, right because
6:20
Speaker 1: math is outside the universe. Beyond the scope of this podcast.
6:25
Speaker 1: That's right. But maybe it's the only thing more fundamental
6:28
Speaker 1: in physics is math. Maybe. I like how you say, maybe,
6:31
Speaker 1: is there is there anything else? Maybe philosophy. I guess
6:34
Speaker 1: philosophy and math, you know, down there at the at
6:37
Speaker 1: the down in the dirt and the roots of human
6:40
Speaker 1: intellectual exploration. Yeah, so lasers are pretty interesting, right, They
6:47
Speaker 1: have an interesting history, Like apparently historians don't really know
6:51
Speaker 1: who invented the laser, or they haven't settled on who
6:55
Speaker 1: invented laser. That's right. And I heard that one really
6:58
Speaker 1: important science historian actually wrote a him about it once.
7:01
Speaker 1: Oh really is that true? Yeah? His name is Um.
7:04
Speaker 1: Hold on, I have it here. Let me check Jorge him.
7:06
Speaker 1: Oh yeah, that comic laureate of the Internet. Should we um?
7:13
Speaker 1: Should we read the poem? Sure? Go for it. I'm
7:17
Speaker 1: not sure if this is supposed to be set to
7:19
Speaker 1: music or rhyme. Yeah, it's supposed to be said to
7:23
Speaker 1: laser music. So you think, think eighties here and then
7:31
Speaker 1: go for it. Um. So, I wrote this when the
7:34
Speaker 1: laser turned fifty about eight years ago, was the anniversary
7:37
Speaker 1: of the laser. I'll read it and you make the
7:39
Speaker 1: pu pu sounds all right. The laser turns fifty this week,
7:43
Speaker 1: an important event in history. But who developed this amazing
7:46
Speaker 1: technique that's still kind of a mystery. Was it Ted
7:51
Speaker 1: my mom who built the first laser? Or was it
7:54
Speaker 1: Towns in Shacklow who wrote the seminal paper and it
7:58
Speaker 1: goes on like that role beautifully crafted versus oh thanks,
8:04
Speaker 1: Yeah it was you know what happened? I was in
8:06
Speaker 1: Ottawa and I went to visit they have a laser
8:09
Speaker 1: institute at one of the university there, and they explained
8:12
Speaker 1: to me that the anniversary of the laser was coming up,
8:14
Speaker 1: and so they explained to me how the laser works.
8:17
Speaker 1: And in fact, I think that's kind of related to
8:19
Speaker 1: how you and I started working together, right, Yeah, you
8:21
Speaker 1: just reminded me of this today. Apparently your comic about
8:25
Speaker 1: the laser is one of the ones that I read
8:27
Speaker 1: and uh and induced me to write you an email.
8:31
Speaker 1: So yeah, the history is kind of funny because the
8:34
Speaker 1: Nobel Prize for the laser, the first prototype for the laser,
8:38
Speaker 1: and the first paper about the laser are all credited
8:42
Speaker 1: to different people, Like, nobody knows who invented this really, yeah,
8:46
Speaker 1: it might have been one of these things where like
8:48
Speaker 1: an idea that whose time has just come, you know,
8:51
Speaker 1: we're on the cusp is sort of the next thing
8:53
Speaker 1: to happen, and a few people contribute bits and pieces here,
8:56
Speaker 1: and some other person puts these things together first there,
8:59
Speaker 1: and uh, it's a bit of a mess. Yeah, it's
9:01
Speaker 1: a bit of a mess. I think it's fascinating. Also
9:03
Speaker 1: how important it is to assign credit for things like
9:07
Speaker 1: we have the laser. It's awesome. Are people just fighting
9:09
Speaker 1: about the money, like who earns a penny every time
9:12
Speaker 1: they make a laser pointer? Or is it about like
9:14
Speaker 1: the credit and scientific history? You know, it's it's interesting
9:18
Speaker 1: to me how how long and nasty this battle is.
9:20
Speaker 1: You mean you wouldn't fight to have that in your tombstone?
9:24
Speaker 1: Daniel Whiteson invented the laser? Who would? Oh, I'm definitely
9:28
Speaker 1: putting that on my tombstone. True or not? I mean,
9:30
Speaker 1: you can put anything you wanted your trimstone. Nobody fact
9:33
Speaker 1: checks tombstones. It's like fake news applied to tombstones. I'm
9:41
Speaker 1: taking credit for all sorts of stuff in my tombstone. Well,
9:43
Speaker 1: let's get into what Daniel is a laser? Right? So
9:48
Speaker 1: a laser is different from a flashlight, right, It's not
9:52
Speaker 1: just a flashlight with a lens, Okay. A laser is
9:54
Speaker 1: something that produces a bunch of light, usually of the
9:59
Speaker 1: same color or so, like all a bunch of photons
10:02
Speaker 1: of the same energy, and they should all be going
10:05
Speaker 1: in the same direction, right, So they're perfectly parallel. Meaning
10:09
Speaker 1: if they're like, you know, a tiny distance apart now,
10:13
Speaker 1: then a hundred meters away or a kilometer away, or
10:16
Speaker 1: a million miles away, they'll still be the same distance apart,
10:19
Speaker 1: perfectly parallel, perfectly parallel photons, right, yeah, exactly, So photons
10:24
Speaker 1: usually of the same color, shot perfectly parallel, and also
10:29
Speaker 1: wiggling the same way. Right. Remember, the photons are waves,
10:33
Speaker 1: and they're like all other particles. They're governed by their
10:36
Speaker 1: wave equation, and waves wiggle, right, they go up and
10:38
Speaker 1: they go down, they go up and they go down.
10:40
Speaker 1: And if you have two waves, if they're wiggling in
10:43
Speaker 1: opposite directions, one wiggles up the other one wiggles down,
10:46
Speaker 1: then they can cancel each other out. Right, So we
10:49
Speaker 1: want our photons all wiggling the same way, so they
10:51
Speaker 1: all sort of pushed together. It's like folks, on a
10:54
Speaker 1: boat rowing at the same time. They all push together
10:57
Speaker 1: for constructive interference to make a strong when they hit
11:01
Speaker 1: something at the end. You want them to be perfectly synchronized.
11:04
Speaker 1: Otherwise they might cancel each other out when they hit something. Yeah,
11:08
Speaker 1: that's right, or they might you know, cancel each other
11:10
Speaker 1: out part of the way. Um. You know these things,
11:12
Speaker 1: these interference effects depend on the phase, and so yeah,
11:16
Speaker 1: you want them all pushing in the same direction, um
11:18
Speaker 1: at the same time. And so that's what a laser produces. Right.
11:21
Speaker 1: That's that's what it means to be a laser. And
11:23
Speaker 1: that's an important distinction of people to understand. That's not
11:26
Speaker 1: just like a powerful flashlight or of uh flashlights somebody
11:29
Speaker 1: put a lens in front of. It's a It's really
11:31
Speaker 1: a very different kind of source of light. It's not
11:34
Speaker 1: just a really bright light. It's like a perfectly ordered,
11:37
Speaker 1: perfectly parallel beams of light. That's right. And there's two
11:40
Speaker 1: kinds of lasers. One kind is the kind we're talking
11:43
Speaker 1: about where all the photons have the same color, so
11:45
Speaker 1: it's monochromatic, right, it's a single color of light, all
11:48
Speaker 1: the photons of the same energy, the same color. UM.
11:51
Speaker 1: That's the kind that you make to produce beams. You
11:53
Speaker 1: can also produce laser pulses, right. These are short bursts,
11:57
Speaker 1: and those require having lots of different colors so that
12:00
Speaker 1: you add they add up and cancel out in just
12:03
Speaker 1: the right way to have a localized burst. And you
12:06
Speaker 1: can add up all the different wiggles together to make
12:09
Speaker 1: the burst of any shape you want, right. And that's
12:11
Speaker 1: different than a flashlight, because a flashlight it's just pumping
12:15
Speaker 1: out photons with all kinds of colors and all kinds
12:19
Speaker 1: of phases, and they're all out of sync with each other,
12:22
Speaker 1: all these photons, that's right. And also they go in
12:24
Speaker 1: in all different directions, right. Um, a flashlight usually has
12:28
Speaker 1: like a tungsten filament bulb or something, right, and that's
12:31
Speaker 1: just glowing and it's sending light in every direction. And
12:34
Speaker 1: even if you have it, you know, coming out of
12:35
Speaker 1: the front, so it's a little bit um shaped. You know.
12:38
Speaker 1: You can take, for example, a flashlight and you can
12:40
Speaker 1: point it at the moon, right, and as as you
12:43
Speaker 1: get further away from the source of the light, the
12:46
Speaker 1: size of the beam grows. Right. Flashlight makes a cone,
12:49
Speaker 1: and the cone grows with distance, So you can point
12:52
Speaker 1: it to the Moon, and you basically cover the whole
12:54
Speaker 1: Moon with your flashlight, because by the time you get
12:57
Speaker 1: to the distance of the Moon, the cone is huge.
12:59
Speaker 1: Even if you focus it with like a lens and
13:01
Speaker 1: try to get them parallel, they won't be perfectly parallel
13:05
Speaker 1: exactly right. There's always going to be some spread there.
13:08
Speaker 1: Whereas with a laser. If you take a laser and
13:10
Speaker 1: you point it at the moon, if you if it's
13:13
Speaker 1: a good laser, when it gets there, should have the
13:15
Speaker 1: beam should have the same with is when is when
13:17
Speaker 1: it left. So that's how that's why lasers are powerful, right,
13:22
Speaker 1: because with just a few photons they can go a
13:26
Speaker 1: great distance together and so they can transmit that information.
13:29
Speaker 1: But they're also kind of in sync so they can
13:31
Speaker 1: deliver all that power when they get there. That's right.
13:34
Speaker 1: And that example about a laser to the Moon is
13:36
Speaker 1: not just like a made up example. I don't know
13:39
Speaker 1: if you know, but the astronauts who visited the Moon
13:41
Speaker 1: left mirrors on the surface of the Moon so that
13:44
Speaker 1: we can bounce lasers off of them and use that
13:46
Speaker 1: to measure the distance from the Earth to the Moon.
13:50
Speaker 1: I think that's pretty cool. The Earth's beak is selfie.
13:52
Speaker 1: You can think we can take a selfie by shooting
13:57
Speaker 1: the laser at the moon. And that's right. Even though
13:59
Speaker 1: this is decades before the concept of selfies, it was
14:03
Speaker 1: it was prescient that way, right. They were forward, forward looking.
14:06
Speaker 1: NASA is always looking into the future. NASA invented the selfie.
14:10
Speaker 1: We just we just give credit. We just give credit
14:12
Speaker 1: to them. They can put it on the Actually the first,
14:15
Speaker 1: the first selfie comes from decades and decades before that.
14:18
Speaker 1: But but yeah, the first astronomical selfie for sure, first
14:21
Speaker 1: laser selfie, that's right. Okay, So that's what the laser is.
14:31
Speaker 1: It's like, it's like something that makes light, that shoots
14:34
Speaker 1: light that's perfectly in sync and perfectly parallel and that's
14:37
Speaker 1: really powerful. Okay, so what why is it called laser?
14:41
Speaker 1: Like what what? What does that acronym mean? Light amplified
14:45
Speaker 1: by stimulated emission radiation. That's right, let's break that down, right.
14:49
Speaker 1: The first one is just light. Okay, so photons are light,
14:52
Speaker 1: that's obvious. The last one, the last one is radiation, right,
14:58
Speaker 1: and radiation in this case also it just means light. Yeah.
15:04
Speaker 1: I think that's because they didn't want to call it
15:06
Speaker 1: a laser that would have been more awkward with an
15:09
Speaker 1: l So both of those words light and radiation just
15:16
Speaker 1: refer to the photons, right, Okay. So it's something that
15:19
Speaker 1: makes light, something that makes light and um and it
15:23
Speaker 1: makes it in this special way using this process called
15:26
Speaker 1: stimulated emission. Okay. And that's the really the guts of
15:30
Speaker 1: the laser. That's what's going on inside, is that it's
15:32
Speaker 1: a system that creates this stimulated emission. So we should
15:35
Speaker 1: dig into that. The A and laser beings amplified, meaning
15:39
Speaker 1: you're not just making that use sort of amplifying it somehow.
15:42
Speaker 1: That's right. The basic principle of the laser is you
15:44
Speaker 1: start with one photon of the color that you want,
15:47
Speaker 1: you know, and you amplify use that to use this
15:50
Speaker 1: system to multiply you. So I want to start with
15:52
Speaker 1: one photon and then you create a chain reaction that
15:55
Speaker 1: gives you ten photons, and then a hundred photons, and
15:57
Speaker 1: then a thousand photons, etcetera, etcetera. Grows exponentially until you
16:01
Speaker 1: have a very very intense beam of photons all the
16:04
Speaker 1: same kind. And the key is the stimulated emission. That's
16:08
Speaker 1: the thing that basically copies the photon. It says, if
16:10
Speaker 1: you have one of the right wavelength or to all
16:13
Speaker 1: the right attributes, then I can make more for you.
16:16
Speaker 1: That's this process called stimulated emission. Okay, let's get stimulated
16:20
Speaker 1: by stimulated emission. But first let's take a quick break. Okay,
16:36
Speaker 1: So laser is something that makes light that's all the
16:40
Speaker 1: same color, the same wavelength, the same direction, the same wiggle,
16:46
Speaker 1: and it's all done by something called stimulated emission. What
16:49
Speaker 1: does that mean? Right? So the thing that's doing the
16:51
Speaker 1: emission is just an atom, and so you have some
16:54
Speaker 1: medium in your laser. Maybe it's a crystal, maybe it's
16:57
Speaker 1: a gas that doesn't really matter, but it's a bunch
16:58
Speaker 1: of atoms. And atoms can emit light, right, any atom,
17:03
Speaker 1: any atom can emit light. Right, you make you get
17:05
Speaker 1: things hot and they glow, right, that's something emitting light.
17:09
Speaker 1: So if you pump energy into some material, right, it
17:12
Speaker 1: will absorb that energy and bring it internally into itself.
17:17
Speaker 1: But then sometimes it gets rid of that energy. That's
17:19
Speaker 1: called emission, and it turns that energy into light. And
17:22
Speaker 1: the way that it does that is it has inside
17:25
Speaker 1: it, it it has these electrons. Right, So every atom has
17:27
Speaker 1: electrons whizzing around it, and there's electrons have a few
17:31
Speaker 1: certain orbits that they can use around the atom. It's
17:35
Speaker 1: like a bunch of different energy levels. Electrons can't just
17:37
Speaker 1: have any random energy level around it atom. Based on
17:41
Speaker 1: the shape of the atom and the configuration of the protons, etcetera.
17:45
Speaker 1: There's a few places the electrons are allowed to live,
17:47
Speaker 1: so they're called energy levels. And you can imagine sort
17:50
Speaker 1: of a ladder of these energy levels. And that's kind
17:52
Speaker 1: of related to their wave nature of electrons, right, because
17:56
Speaker 1: their waves they can only fit in so many ways
18:00
Speaker 1: around the atom. Right, It's sort of related to that, right,
18:03
Speaker 1: It's very closely related. Yeah. Um, the reason that there
18:06
Speaker 1: are discrete energy levels, right, quantized energy levels, is precisely
18:10
Speaker 1: because of those waves and the way the waves fit
18:13
Speaker 1: together around the atom. So a simple way to think
18:15
Speaker 1: about it is when the electron goes around the atom,
18:18
Speaker 1: it's going to do it's wiggling, and you wanted to
18:21
Speaker 1: build on itself. You don't want it to cancel itself out,
18:23
Speaker 1: and so when it comes around one orbit, you need
18:27
Speaker 1: to be in the same place in its wiggle either
18:29
Speaker 1: it's wiggling up or it's wiggling down. It has to
18:31
Speaker 1: fit a very specific number of wiggles in an orbit.
18:35
Speaker 1: You can just do like three and a half that's right.
18:38
Speaker 1: It has to wiggle once or twice or three times. Right.
18:42
Speaker 1: If it wiggles one and a half times, then it's
18:45
Speaker 1: going to get out of sync with itself and eventually
18:47
Speaker 1: cancel itself out. So those are not stable solutions. So
18:50
Speaker 1: you can't have an electron hanging out and wiggling one
18:53
Speaker 1: and a half times around the atom. So each of
18:55
Speaker 1: those is a different level. It's not like the Earth
18:57
Speaker 1: going around the Sun, like if something moves as a
18:59
Speaker 1: little bit, our orbit will increase a little bit. That's
19:02
Speaker 1: not how electrons work. They have very specific orbits that
19:06
Speaker 1: can fit around the nucleus of the atom. Yeah, that's
19:09
Speaker 1: actually a really interesting deep question. Is the Earth's orbit quantized?
19:14
Speaker 1: Are there an infinite number of orbits? That's not a
19:17
Speaker 1: one with a simple answer. If gravity is not quantum mechanical,
19:21
Speaker 1: then you're right, so there's an infinite number of orbits
19:24
Speaker 1: the Earth can take. However, if the gravity is quantized,
19:27
Speaker 1: then then you're wrong, and there are energy levels around
19:31
Speaker 1: the Sun, but those energy levels would be so tiny
19:33
Speaker 1: we could probably not even see them anyway. That might
19:35
Speaker 1: be the subject of a different podcast. Yeah, exactly. Yeah.
19:40
Speaker 1: So the energy, So the electron has these energy levels
19:42
Speaker 1: it has on these ladder. This ladder can go up
19:44
Speaker 1: and it can go down. Yeah, people use the ladder analogy, right,
19:47
Speaker 1: like electrons can be here or it can go up
19:49
Speaker 1: a level or another level. Right, It's like very discrete steps.
19:54
Speaker 1: And just like with the ladder, what happens when you
19:56
Speaker 1: go up a level? Will you It takes some energy
19:58
Speaker 1: to do that, right, put some energy into your thigh
20:01
Speaker 1: muscle to push you up, and then you're storing more
20:04
Speaker 1: energy or you have more gravitational energy because you're higher up.
20:07
Speaker 1: The same thing happens with the electron. How does it
20:09
Speaker 1: go up a level? It needs to get energy from somewhere, right,
20:12
Speaker 1: it needs to get heated up or absorb some light
20:15
Speaker 1: or something. So it can go up a level, right,
20:18
Speaker 1: and then it can go down a level. And what
20:20
Speaker 1: happens when it goes down a level While the energy
20:22
Speaker 1: level it was at is fixed and the energy level
20:25
Speaker 1: is going to is fixed, so the energy difference between
20:27
Speaker 1: them is fixed, meaning every atom has the same levels.
20:31
Speaker 1: And if electrons jumped down from one level to the
20:34
Speaker 1: lower one. Then they're going to release a photon whose
20:38
Speaker 1: energy is exactly the difference between those two levels, right,
20:41
Speaker 1: conservation of energy. The electron loses energy, goes down a level,
20:45
Speaker 1: and it gives off that missing that extra energy in
20:48
Speaker 1: terms of a photon. Okay, so the electron goes down
20:50
Speaker 1: a level, it will shoot out a photon with that
20:53
Speaker 1: energy that it doesn't need anymore. That's right, exactly. So
20:57
Speaker 1: how do you get a bunch of photons of all
20:59
Speaker 1: the same color in the same direction. When you get
21:01
Speaker 1: a bunch of atoms, You get them all to have
21:04
Speaker 1: their electrons up one level, right, You heat them up,
21:06
Speaker 1: you pump some energy into them somehow, and then you
21:09
Speaker 1: get them to come down all about the same time.
21:12
Speaker 1: You get them excited. You get him excited, right, and
21:14
Speaker 1: then you get them the big let down. Yeah, all,
21:19
Speaker 1: And when they get the let down, that's when they
21:22
Speaker 1: give off a photon, and each one will give off
21:24
Speaker 1: the same color photon. The photon is determined exactly by
21:30
Speaker 1: its energy, which is determined by its wavelength. Right, those
21:33
Speaker 1: things things are all connected, right, But they don't all
21:35
Speaker 1: in a laser. They don't all give them out at
21:37
Speaker 1: the same time, it's it's kind of like how you
21:39
Speaker 1: said earlier. You want to cause a chain reaction that
21:42
Speaker 1: will make all the atoms in your laser shoot all
21:45
Speaker 1: these photons perfectly saying exactly so that chain reaction is key,
21:49
Speaker 1: and you can have an atom and you can give
21:52
Speaker 1: it energy. So the electron goes up one level and
21:54
Speaker 1: then it's happened to just hang out there for a while, right,
21:57
Speaker 1: But what happens when another photon just the right energy
22:01
Speaker 1: level comes by, Like if you're an electron, you're an
22:03
Speaker 1: excited state, um, and there's like a ladders step ladder
22:07
Speaker 1: step below you, or you could go down. If a
22:10
Speaker 1: photon comes by just that right energy level, it has
22:13
Speaker 1: exactly the energy that's between you and that lower level,
22:16
Speaker 1: then you're more likely to emit. You get pushed sort
22:19
Speaker 1: of out of that energy level. And the reason is
22:22
Speaker 1: that that photon changes the way the environment works. Right.
22:25
Speaker 1: Photons are electromagnetic waves, so it creates a little electromagnetic
22:29
Speaker 1: field there that makes what you were doing a little
22:32
Speaker 1: less stable, so sort of pushes you out of that
22:35
Speaker 1: state down to a lower state, and you end up
22:37
Speaker 1: emitting another photon. So the bottom line is if you're
22:41
Speaker 1: capable of emitting that photon, and one photon just like
22:44
Speaker 1: that comes by, then you're gonna give it up and
22:46
Speaker 1: emit that photon. And that's why it's called stimulated emission. Right, Like,
22:51
Speaker 1: if you're an excited atom, you could just spontaneously have
22:55
Speaker 1: your electron drop and admit a photon. That's called spontaneous emission. Yeah,
23:00
Speaker 1: But stimulated emission is when you're excited and you get
23:03
Speaker 1: hit by another photon and that causes you to drop
23:07
Speaker 1: a level and emit another photon. Yeah. It's sort of
23:10
Speaker 1: like peer pressure and you're like, hey, everybody's emitting that
23:13
Speaker 1: red photon. I got one, I could emit one, and yeah,
23:17
Speaker 1: yeah I could, and so I will. This is the
23:19
Speaker 1: right time, you know. And so that's what the stimulated
23:22
Speaker 1: part is. Right, Um, it's not. This is not nocturnal emissions.
23:25
Speaker 1: People were talking about photons stimulating electrons into a emitting
23:30
Speaker 1: war photons. What's the acronym for that one? Leaner? Um?
23:41
Speaker 1: So to review, right, you start, you get some material,
23:44
Speaker 1: you gotta pump it with energy. It's not free energy, right,
23:46
Speaker 1: you gotta pump it with energy somehow. You gotta get
23:48
Speaker 1: the atoms excited in your media and lock of stuff. Yeah,
23:53
Speaker 1: it's like you know your comedy routine. You need somebody
23:55
Speaker 1: go out there and warm up the crowd. Right, So
23:57
Speaker 1: first you warm up the crowd, you get it's called
24:00
Speaker 1: population inversion. Maybe've heard that phrase by everyone a beer,
24:05
Speaker 1: that's right, We've discovered alcohol makes people laugh at the
24:08
Speaker 1: jokes more. And so the physics equivalent for lasers, right,
24:13
Speaker 1: is you pump the room with with energy and you
24:17
Speaker 1: get all those electrons up at that level, and then
24:20
Speaker 1: one of them will one of them will pop, right,
24:23
Speaker 1: and that will cause the chain reaction. Having one photon
24:25
Speaker 1: around will make all these other atoms which you know
24:28
Speaker 1: are holding that photon inside them. Basically, birds didn't get
24:31
Speaker 1: rid of it. They'll start emitting and then and then
24:33
Speaker 1: more and more will admit. But they have to get
24:35
Speaker 1: hit by a photon for them to release a photon, right, Like,
24:40
Speaker 1: it doesn't just yeah, it's not because your neighbor shot
24:43
Speaker 1: out a photon, then you shoot out a photon. It's
24:45
Speaker 1: like you got you have to get hit by a
24:47
Speaker 1: photon for you to get stimulated. Yeah, you don't have
24:50
Speaker 1: to absorb it, but having the photon nearby close enough
24:53
Speaker 1: to interact with the atom will change the electromagnetic vicinity
24:57
Speaker 1: essentially and cause it to do that. And that's why
24:59
Speaker 1: you usually you also put this block of atoms in
25:02
Speaker 1: a resonant cavity. Basically you put two mirrors on either
25:04
Speaker 1: side so that you capture the photons and you sort
25:08
Speaker 1: of bounce them around inside. It's the same reason why
25:10
Speaker 1: you have like walls in your oven, right, you want
25:12
Speaker 1: to reflect the energy back so that it builds on itself. Right.
25:16
Speaker 1: But that that whole process I heard is still even
25:20
Speaker 1: a mystery for physicists, Like why exactly does the stimulated
25:24
Speaker 1: atom shootout a photon that's exactly exactly like the one
25:29
Speaker 1: that just went by closely or that hit it. Why
25:31
Speaker 1: does it create a photon that's exactly identical to the
25:34
Speaker 1: one that it saw with the same like wiggle and
25:37
Speaker 1: the same timing in this exact same direction. That's still
25:41
Speaker 1: kind of a mystery, right. Well, I think there's some
25:43
Speaker 1: quantum mechanical arguments that that suggested. I think there's a
25:47
Speaker 1: lot of the details are not perfectly understood. But you know,
25:50
Speaker 1: the photon creates destabilizes the atom a tiny bit, right,
25:55
Speaker 1: and so we can understand that there's something called firms
25:57
Speaker 1: Golden rule, which tells us about how how things like
26:00
Speaker 1: to decay, and so having that photon around definitely helps
26:04
Speaker 1: us understand how the electron would be more likely to
26:08
Speaker 1: jump down. Um. But yeah, why why it comes out
26:12
Speaker 1: in exactly the same phase for example, I think it's
26:14
Speaker 1: more likely too, but not guaranteed. So I think there
26:16
Speaker 1: definitely are some some open questions there before we keep going,
26:20
Speaker 1: Let's take a short break. Okay, So that's the S
26:36
Speaker 1: E N L A S E R and so we
26:39
Speaker 1: we tried. We covered all the letters. So it's light
26:41
Speaker 1: amplified by stimulated emission radiation, that's right, and um. And
26:47
Speaker 1: so you have it in this box and you have
26:48
Speaker 1: these residents. You have a resident cavity. You have either mirrors, right,
26:51
Speaker 1: bounce it back and forth, so the photons you emit
26:54
Speaker 1: more photons to emit and um. You know, you can
26:57
Speaker 1: have a little hole in the side so that some
26:58
Speaker 1: of them leak out, and that's basically your laser. That's
27:01
Speaker 1: how you produce it, right. But it can be a
27:03
Speaker 1: constant thing. You can be constantly pumping it with energy,
27:06
Speaker 1: pushing the electrons up and then they come down. You
27:08
Speaker 1: get photon, you push them back up right so it
27:11
Speaker 1: can be a continual thing. Um. One of the most
27:14
Speaker 1: interesting lasers I ever saw was actually here on on
27:16
Speaker 1: campus at U SEE. I as a professor here Franklin
27:19
Speaker 1: Dollar who does fusion research, and they're trying to create
27:22
Speaker 1: fusion by focusing a bunch of lasers all in the
27:24
Speaker 1: same place. And he had this amazing setup where had
27:27
Speaker 1: a bunch of lasers all overlapping in his lab and
27:31
Speaker 1: he created a ball of plasma that was just floating
27:35
Speaker 1: there in empty space. It was incredible. You can trap
27:39
Speaker 1: atoms with lasers basically, right, you can do that, but
27:42
Speaker 1: here he was just basically heating the air with a
27:45
Speaker 1: bunch of lasers. By pointing a bunch of lasers so
27:47
Speaker 1: they overlapped in one place in space. He heated up
27:50
Speaker 1: the air hot enough to ionize and create a floating
27:53
Speaker 1: ball of plasma. It was like looking at stable lightning.
27:56
Speaker 1: It was pretty incredible. But these are These mirrors are
27:59
Speaker 1: pretty cool because they're not just any mirrors that you
28:02
Speaker 1: put on both sides of your stimulated stuff. It's like
28:06
Speaker 1: one of them has to be a one way mirror.
28:09
Speaker 1: One of them is a regular mirror, but the other
28:11
Speaker 1: one is like a half mirror, meaning that it reflects
28:14
Speaker 1: some of the light, but it also lets through some
28:16
Speaker 1: of the light. Right, that's right. If both of them
28:18
Speaker 1: were perfect mirrors, then you would never get anything out
28:20
Speaker 1: of your laser. You just they would all stay inside
28:23
Speaker 1: the cavity. So you have to have one of them
28:25
Speaker 1: being imperfect mirrors that some of them leak out. Yeah,
28:27
Speaker 1: So that that's kind of where the laser is. It's
28:29
Speaker 1: kind of like a light echo chamber. Meaning you get
28:33
Speaker 1: you get all your atoms excited, and then you set
28:36
Speaker 1: one one of them off and then that will, for example,
28:41
Speaker 1: go to the right, bounce off the mirror, go to
28:44
Speaker 1: the left, hit another atom, cause it to also admit
28:48
Speaker 1: an exact copy of that photon hit the other mirror.
28:51
Speaker 1: Then both of them come back to the stuff, and
28:53
Speaker 1: then they stimulate two other atoms, and then that creates
28:55
Speaker 1: four photons and that just kind of builds and multiplies
28:59
Speaker 1: within your echo chamber. But because one of the mirrors
29:02
Speaker 1: is one way or semi transparent, that's where the laser
29:06
Speaker 1: shoots out. Right, Yeah, yeah, exactly. Did I just make
29:08
Speaker 1: that up? You should be the physicist on this podcast, man,
29:15
Speaker 1: But I mean that's that's an important part of it. Right.
29:17
Speaker 1: It's like you have you want to develop an echo chamber,
29:19
Speaker 1: but you have to let some of the light out,
29:21
Speaker 1: that's right. Yeah, If you don't let some of that out,
29:23
Speaker 1: then it's pretty quickly going to get overheated. You're gonna
29:27
Speaker 1: laser your own laser, right, And it's for all those
29:31
Speaker 1: for all of us who have ever built a death star.
29:33
Speaker 1: You know that you want it to blow up your
29:36
Speaker 1: enemies basis, you don't want it to destroy your own.
29:45
Speaker 1: But then it's stimulating the stuff in between. You can
29:48
Speaker 1: do that several ways. Like your stuff can be a
29:51
Speaker 1: gas or it can be crystal to right, that's right.
29:54
Speaker 1: And if you want a laser to give you light
29:57
Speaker 1: of a certain wavelength, like you want a red laser
30:00
Speaker 1: or a green laser, or an X ray laser or something,
30:03
Speaker 1: you have to find a material that has steps in
30:07
Speaker 1: the ladder, their steps in their electron ladder that are
30:10
Speaker 1: just the right size. Right. You can't just tune it
30:12
Speaker 1: up to anything you want, right, You can't say I
30:15
Speaker 1: want photons of this frequency. You have to find some
30:18
Speaker 1: material that has electrons um that have an energy level
30:22
Speaker 1: that has just the right size and that's why some
30:25
Speaker 1: of these things are easy, and some of these things
30:27
Speaker 1: are hard, like X ray lasers are really difficult to build,
30:31
Speaker 1: and they're really everywhere, right, Like I was thinking, like
30:34
Speaker 1: if you have a mouse in your computer and it's
30:36
Speaker 1: an optical mouse that has a little laser in it, right,
30:38
Speaker 1: that's right, Yeah, yeah, lasers are everywhere, and uh, it's
30:42
Speaker 1: amazing how influential they have become. You know. And if
30:46
Speaker 1: you look back at the history of the lasers, not
30:47
Speaker 1: only is it a big mess nobody can agree about
30:50
Speaker 1: who invented them, but in the early days there was
30:53
Speaker 1: a lot of skepticism that it was even useful at all. Right,
30:57
Speaker 1: some scientists thought it was impossible to make a laser, right, Yeah,
31:01
Speaker 1: it was Neil's bore. He tried to make an argument
31:03
Speaker 1: using the Heisenberg and certainty principle. He was like, you
31:06
Speaker 1: can't have that many atoms in a specified state. He
31:09
Speaker 1: thought it would just be impossibly that quantum mechanics would
31:12
Speaker 1: make it not possible to make a laser, when in fact,
31:14
Speaker 1: you need quantum mechanics to build a laser. Right, So
31:17
Speaker 1: it works the other direction, So sometimes famous scientists get
31:20
Speaker 1: it wrong. What was his argument for saying that it
31:23
Speaker 1: was impossible, Well, you know, the Heisenberg and certainty principle
31:26
Speaker 1: tells you that there's a certain there's a limit to
31:29
Speaker 1: how much information you can have, right, And so he
31:32
Speaker 1: was arguing that having all these atoms in the same state,
31:35
Speaker 1: that you're specifying their energy um too tightly, right, you
31:40
Speaker 1: can't the same way the Heisenberger and certainty principle tells
31:43
Speaker 1: you that you can't know the position and momentum um
31:47
Speaker 1: of a particle at the same time. It also applies
31:50
Speaker 1: to the energy and timing information, and so a laser
31:54
Speaker 1: is trying to isolate a bunch of particles have the
31:57
Speaker 1: same energy all at the same time. And so he
31:59
Speaker 1: thought that that was going to violate the Heisenberg on
32:01
Speaker 1: certainly principle. But clearly it doesn't. We shot that down
32:06
Speaker 1: with a laser's right, with our fully operational battle station.
32:12
Speaker 1: So so there's, uh, it's interesting that there are all
32:15
Speaker 1: kinds of different kinds of laser right, Right, Like your
32:17
Speaker 1: mouse can have a laser on it, but you can
32:19
Speaker 1: also use a laser to cut through steel, right, Like,
32:23
Speaker 1: what's the difference between the laser and my mouse and
32:26
Speaker 1: the laser that can cut through things nothing, you're a mouse.
32:29
Speaker 1: Laser can cut through steel, horrey, you just never tried. Know.
32:33
Speaker 1: The difference is just the intensity, right, the number of
32:35
Speaker 1: photons per second. Photons have energy, and when something is
32:39
Speaker 1: hit by a laser, they deposit their energy into whatever
32:42
Speaker 1: is hit by it. If it's not a very bright laser,
32:45
Speaker 1: then you're not I don't have a whole lot of
32:46
Speaker 1: photons per second, then you're not depositing a lot of energy, right.
32:50
Speaker 1: So that's why you can shine you know, a simple
32:53
Speaker 1: laser pointer and as your skin and it doesn't burn, right,
32:57
Speaker 1: But if you had ten thousand laser point and you
33:00
Speaker 1: hit them all at the same place in your skin,
33:02
Speaker 1: that would be the same as having one really powerful laser,
33:05
Speaker 1: and yeah, you could cut a hole in yourself. So
33:07
Speaker 1: cutting lasers are just lasers with a higher intensity UM
33:11
Speaker 1: and they can have more photons per second and they
33:13
Speaker 1: do that. How do you create more intensity? Do you
33:15
Speaker 1: just pump the material more or do you do you
33:19
Speaker 1: know what I mean? Like, what's the difference. If I
33:20
Speaker 1: had the same material, how do I get more laser
33:23
Speaker 1: out of it? Yeah, you can pump the material more,
33:25
Speaker 1: you can have more material. Um you're gonna have you
33:28
Speaker 1: must be must also have to do with how you
33:30
Speaker 1: tune the one wayness of your one way mirror how much,
33:34
Speaker 1: And that's that's some fracture of the energy out per second.
33:37
Speaker 1: So there's probably lots of ways to do it. Well.
33:39
Speaker 1: Lasers are everywhere in our lives. But I heard somebody
33:42
Speaker 1: once told me that the biggest impact lasers have had
33:46
Speaker 1: is in science, helping us make instruments to measure things
33:50
Speaker 1: so that we can expand our knowledge about the universe. Um. Yeah,
33:55
Speaker 1: lasers everywhere. Um, but I thought you were going to
34:02
Speaker 1: say something about like laser lithography, like we can all
34:05
Speaker 1: design our own cutting board logos and have lasers burn
34:09
Speaker 1: them out. Yeah. No, the maker, the maker movement is
34:12
Speaker 1: very grateful for lasers, but in the sense that you know,
34:15
Speaker 1: like that's how we know for example, or initially that's
34:18
Speaker 1: how we kind of figured out that the gravitational waves
34:21
Speaker 1: measurement that depends on lasers, right, absolutely. Yeah. That uses
34:24
Speaker 1: two lasers um in two different directions, and then you
34:28
Speaker 1: shoot them away and they bounce back and use that
34:30
Speaker 1: as a way to measure the distance. You count the
34:32
Speaker 1: number of wiggles the laser has had. Yeah, Yeah, and
34:35
Speaker 1: that's how they do a lot of like DNA studies,
34:38
Speaker 1: and you can use lasers to figure out what materials
34:43
Speaker 1: are made out of. So it's kind of in scientific
34:46
Speaker 1: instrumentation has been a huge Lasers have had had a
34:50
Speaker 1: huge impact, not just in like consumer products and death
34:54
Speaker 1: rays that were never made, it's in science, right, it's
34:57
Speaker 1: in its Lasers have really kind of boosted and amplified
35:01
Speaker 1: what science can do. And that's right. Yeah, we're all
35:03
Speaker 1: emitting more papers thanks to lasers. We're stimulated to emit
35:07
Speaker 1: more papers. Yeah. Lasers also play a big role in
35:10
Speaker 1: fusion research, as we were mentioning earlier. Um, you know
35:13
Speaker 1: it's a powerful device, right, you have you have light
35:16
Speaker 1: with a specific wavelength. You can focus at a very
35:18
Speaker 1: specific spot and so it uh, and that's what scientists do,
35:22
Speaker 1: you know, They think, how can I answer this question
35:24
Speaker 1: with the tools I have? And that's a very specific tool.
35:27
Speaker 1: It's like a tiny little science scalpel, right, and that
35:31
Speaker 1: lets you sometimes cut problems open that you otherwise couldn't. Yeah.
35:35
Speaker 1: So the next time you are at the grocery store
35:37
Speaker 1: and are checking out and you hear that people, that's
35:41
Speaker 1: a that's a laser at work. There there's a little
35:43
Speaker 1: tiny death ray death ray to scan your your bananas.
35:49
Speaker 1: That's right, you're fully operational grocery store uses lasers. Yeah,
35:55
Speaker 1: all right. Well, I hope this discussion stimulated you and
36:00
Speaker 1: made you focus with laser pocisition. And if you have
36:03
Speaker 1: any questions, you can admit them to us. We'd love
36:06
Speaker 1: to hear him see you next time. If you still
36:16
Speaker 1: have a question after listening to all these explanations, please
36:19
Speaker 1: drop us a line. We'd love to hear from you.
36:22
Speaker 1: You can find us at Facebook, Twitter, and Instagram at
36:25
Speaker 1: Daniel and Jorge that's one word, or email us at
36:28
Speaker 1: Feedback at Daniel and Jorge dot com.