WEBVTT - How Does A Laser Work? 0:00:07.040 --> 0:00:10.399 Hey, Daniel, let's talk about acronyms. Acronyms are actually a 0:00:10.520 --> 0:00:13.240 really really important part of science. Whenever you have a 0:00:13.240 --> 0:00:15.880 good idea, you have to come up with an acronym 0:00:15.960 --> 0:00:17.480 or it's not going to be catchy. Well, I heard 0:00:17.480 --> 0:00:21.240 there have been some pretty unfortunate acronyms in the history 0:00:21.280 --> 0:00:24.880 of science. There are I googled for worst acronyms ever, 0:00:25.000 --> 0:00:27.200 and I came up with some that you gotta wonder, 0:00:27.320 --> 0:00:31.240 like people must have known what was going on, you know. So, um, 0:00:31.280 --> 0:00:37.479 one of my favorites is Phase one Observing Proposal System. 0:00:37.479 --> 0:00:40.120 So for those of you filing along at home, that's 0:00:40.240 --> 0:00:43.800 p O O P S. So yeah, you can put 0:00:43.800 --> 0:00:47.279 that together yourself. But but I heard that one day 0:00:47.320 --> 0:00:51.160 actually grabbed the y from system, like they consciously made 0:00:51.159 --> 0:00:54.240 the choice not to be called poops but to be 0:00:54.280 --> 0:00:58.480 called poop. See, well, there is one acronym that's a 0:00:58.520 --> 0:01:02.000 famous acronym for a physics topic. But I think we 0:01:02.120 --> 0:01:05.360 think maybe most people don't even know it's an acronym. Yeah, 0:01:05.360 --> 0:01:08.000 And maybe that means it's really successful, right, because it's 0:01:08.040 --> 0:01:10.600 become a word in its own right. You know, people 0:01:10.640 --> 0:01:14.200 actually use the word yeah, and that word is laser 0:01:14.440 --> 0:01:17.959 camp to do. So, do you know what it stands for? Horror? Hey, 0:01:18.000 --> 0:01:19.480 don't look it up. Do you know what it stands for? 0:01:20.360 --> 0:01:24.839 Test NERD CREB test, I do it. It stands for 0:01:25.000 --> 0:01:32.360 UM light amplification through stimulated emission radiation. Being we have 0:01:32.480 --> 0:01:35.080 a winner, folks, give him a laser. But I heard 0:01:35.120 --> 0:01:37.640 that the acron could have been different. It could have 0:01:37.680 --> 0:01:42.959 been light oscillation by stimulated emission radiation. That's right, And 0:01:42.959 --> 0:01:44.800 I don't think that one would have caught on quite 0:01:44.800 --> 0:01:47.240 as well. That would be l o s E er 0:01:47.640 --> 0:01:50.800 has some obvious disadvantages. You don't want to be a 0:01:50.800 --> 0:02:14.120 loser scientist. That would be That would be obvious him 0:02:14.800 --> 0:02:17.600 and I'm Daniel, and welcome to our podcast Daniel and 0:02:17.680 --> 0:02:21.840 Jorge Explain the Universe, in which we talk about all 0:02:21.919 --> 0:02:24.280 kinds of cool things about the universe. Yeah, and we 0:02:24.480 --> 0:02:27.320 take the universe apart, we disassemble its acronyms, and we 0:02:27.360 --> 0:02:29.920 tell you what it actually means. All the cool things 0:02:29.919 --> 0:02:33.840 you see in science fiction movies, books, laser guns, stuff 0:02:33.880 --> 0:02:35.960 like that. We break it down and make sense of 0:02:35.960 --> 0:02:38.240 it for you. So, if you have ideas for what 0:02:38.320 --> 0:02:40.920 you'd like us to talk about, send them into feedback 0:02:40.960 --> 0:02:44.200 at Daniel and Jorge dot com. We love hearing your 0:02:44.200 --> 0:02:46.840 topic suggestions. Today on the program, we're going to be 0:02:46.840 --> 0:02:56.920 talking about lasers, lasers. How does a laser work? What 0:02:57.080 --> 0:02:59.680 is a laser? Who came up with a laser? Where 0:02:59.680 --> 0:03:02.840 can I at my laser death ray? These are important questions. 0:03:02.880 --> 0:03:04.720 How can I make it my living to laz about? 0:03:06.960 --> 0:03:12.200 Here a cartoonist, you're already laser by which I mean 0:03:12.240 --> 0:03:17.720 you are brilliant and cutting. That's right, and very um focused, 0:03:18.600 --> 0:03:24.280 very focused exactly. So, Yeah, lasers are. Lasers are awesome. 0:03:24.360 --> 0:03:26.799 Everyone knows what a laser is. My kids know what 0:03:26.919 --> 0:03:31.160 lasers are. Yeah, I mean they're they're in science fiction everywhere. Um, 0:03:31.320 --> 0:03:34.480 people have laser pens, right, lasers there. You probably have 0:03:34.600 --> 0:03:38.320 dozens of lasers in your house, right, Lasers used for everything? Yeah, 0:03:38.360 --> 0:03:41.200 they're in our everyday lives. Like every time you go 0:03:41.360 --> 0:03:43.680 buy something at a store. Assume you still go to 0:03:43.760 --> 0:03:47.080 physical store. But if they scan your product in they're 0:03:47.160 --> 0:03:50.040 using a laser, that's right. And if you still have 0:03:50.080 --> 0:03:52.400 a CD player, that thing is read by a laser. 0:03:52.840 --> 0:03:56.440 A CD what you're too young to understand those things? 0:03:56.480 --> 0:03:59.440 For he For those of you under forty we used 0:03:59.440 --> 0:04:02.839 to store music on these shiny little disks. Yeah, they'd 0:04:02.880 --> 0:04:06.680 use lasers. So they were literally everywhere. I mean, there 0:04:06.680 --> 0:04:09.680 are optical drives, right, anything that reads the disc. So 0:04:09.720 --> 0:04:12.000 if you pop in a disk to your PlayStation, that's 0:04:12.080 --> 0:04:14.320 using a laser in there, that's right. And lasers have 0:04:14.320 --> 0:04:17.560 an enormous variety of applications, you know, from tiny laser 0:04:17.600 --> 0:04:22.240 pointers to world size lasers that people are experimenting with 0:04:22.320 --> 0:04:26.200 to try to deflect asteroids that might blow up the Earth. Yeah, 0:04:26.279 --> 0:04:29.680 like in the Dead Star and in Star Wars, right, 0:04:29.880 --> 0:04:32.480 that's right. Those that's the fiction, of course, But the 0:04:32.520 --> 0:04:36.640 group building a laser to disflect asteroids, that's real. They 0:04:36.680 --> 0:04:39.440 might save the planet. They might save the planet exactly. 0:04:39.680 --> 0:04:43.000 So lasers are everywhere. They're definitely an important part of 0:04:43.000 --> 0:04:46.560 our culture and of our technology and of everything you do. 0:04:47.080 --> 0:04:49.760 But the question we had was how do they do 0:04:49.839 --> 0:04:52.320 what they do? What does it mean to lazy? How 0:04:52.320 --> 0:04:55.120 do you build a laser? Could you assemble one from 0:04:55.120 --> 0:04:57.520 the stuff in your kitchen? Yeah? Can you shoot it 0:04:57.560 --> 0:05:00.680 in the movies like to destroy other specihopes? That's right? 0:05:00.720 --> 0:05:04.080 Do they really make the pew pew pew sound. That's 0:05:04.160 --> 0:05:05.880 that's the question. I want to know the answer to 0:05:07.080 --> 0:05:09.520 what sound does a laser make? Is it like pure 0:05:09.880 --> 0:05:16.279 or it's definitely one of those? How good? I hit 0:05:16.360 --> 0:05:19.960 it on my first three talk tries. But we were 0:05:20.000 --> 0:05:23.240 wondering how many people out there know what a laser 0:05:23.680 --> 0:05:26.200 is and how it works. I walked around on campus 0:05:26.200 --> 0:05:28.520 and I asked people, do you know how a laser works? 0:05:28.680 --> 0:05:30.680 Does of you listening think about it for a second. 0:05:31.920 --> 0:05:38.400 Here's what people had to say, mate, Sorry, uh, focused light, 0:05:39.720 --> 0:05:46.280 light gets multiplied and focused? Okay, cool light? All right. 0:05:46.440 --> 0:05:49.239 I guess not a lot of deep knowledge about lasers 0:05:49.279 --> 0:05:52.000 out there. I had the impression people think lasers are 0:05:52.040 --> 0:05:54.120 like you have a light bulb and then maybe you 0:05:54.200 --> 0:05:56.440 have a lens to focus it, and that's your laser. 0:05:57.080 --> 0:05:58.760 I like the person who said, how did how do 0:05:58.839 --> 0:06:03.279 lasers work? By light? Technically? You're right, you can go 0:06:03.360 --> 0:06:06.359 wrong with that answer. That's right. Yeah, go with a 0:06:06.520 --> 0:06:09.760 very very general answer, how does this work? Physics? Right? 0:06:09.760 --> 0:06:12.640 You could just say physics to any question to ask people? Really, 0:06:12.680 --> 0:06:17.479 even math? Can I say how does math work? No? 0:06:17.640 --> 0:06:20.719 But that's not a topic for our podcast, right because 0:06:20.760 --> 0:06:24.479 math is outside the universe. Beyond the scope of this podcast. 0:06:25.440 --> 0:06:28.320 That's right. But maybe it's the only thing more fundamental 0:06:28.360 --> 0:06:31.520 in physics is math. Maybe. I like how you say, maybe, 0:06:31.760 --> 0:06:34.400 is there is there anything else? Maybe philosophy. I guess 0:06:34.480 --> 0:06:37.760 philosophy and math, you know, down there at the at 0:06:37.760 --> 0:06:40.559 the down in the dirt and the roots of human 0:06:40.600 --> 0:06:47.320 intellectual exploration. Yeah, so lasers are pretty interesting, right, They 0:06:47.320 --> 0:06:51.520 have an interesting history, Like apparently historians don't really know 0:06:51.839 --> 0:06:55.040 who invented the laser, or they haven't settled on who 0:06:55.120 --> 0:06:58.000 invented laser. That's right. And I heard that one really 0:06:58.040 --> 0:07:00.880 important science historian actually wrote a him about it once. 0:07:01.200 --> 0:07:04.120 Oh really is that true? Yeah? His name is Um. 0:07:04.160 --> 0:07:06.560 Hold on, I have it here. Let me check Jorge him. 0:07:06.800 --> 0:07:13.400 Oh yeah, that comic laureate of the Internet. Should we um? 0:07:13.400 --> 0:07:17.280 Should we read the poem? Sure? Go for it. I'm 0:07:17.320 --> 0:07:19.680 not sure if this is supposed to be set to 0:07:19.840 --> 0:07:23.560 music or rhyme. Yeah, it's supposed to be said to 0:07:23.640 --> 0:07:31.120 laser music. So you think, think eighties here and then 0:07:31.200 --> 0:07:34.040 go for it. Um. So, I wrote this when the 0:07:34.160 --> 0:07:37.520 laser turned fifty about eight years ago, was the anniversary 0:07:37.520 --> 0:07:39.480 of the laser. I'll read it and you make the 0:07:39.480 --> 0:07:42.920 pu pu sounds all right. The laser turns fifty this week, 0:07:43.360 --> 0:07:46.800 an important event in history. But who developed this amazing 0:07:46.840 --> 0:07:51.520 technique that's still kind of a mystery. Was it Ted 0:07:51.800 --> 0:07:54.680 my mom who built the first laser? Or was it 0:07:54.720 --> 0:07:58.320 Towns in Shacklow who wrote the seminal paper and it 0:07:58.360 --> 0:08:03.520 goes on like that role beautifully crafted versus oh thanks, 0:08:04.120 --> 0:08:06.240 Yeah it was you know what happened? I was in 0:08:06.320 --> 0:08:09.120 Ottawa and I went to visit they have a laser 0:08:09.160 --> 0:08:12.040 institute at one of the university there, and they explained 0:08:12.040 --> 0:08:14.160 to me that the anniversary of the laser was coming up, 0:08:14.440 --> 0:08:16.440 and so they explained to me how the laser works. 0:08:17.000 --> 0:08:18.960 And in fact, I think that's kind of related to 0:08:19.000 --> 0:08:21.720 how you and I started working together, right, Yeah, you 0:08:21.800 --> 0:08:25.240 just reminded me of this today. Apparently your comic about 0:08:25.280 --> 0:08:27.800 the laser is one of the ones that I read 0:08:27.920 --> 0:08:31.320 and uh and induced me to write you an email. 0:08:31.480 --> 0:08:34.080 So yeah, the history is kind of funny because the 0:08:34.120 --> 0:08:38.600 Nobel Prize for the laser, the first prototype for the laser, 0:08:38.880 --> 0:08:42.960 and the first paper about the laser are all credited 0:08:42.960 --> 0:08:46.760 to different people, Like, nobody knows who invented this really, yeah, 0:08:46.840 --> 0:08:48.640 it might have been one of these things where like 0:08:48.800 --> 0:08:51.240 an idea that whose time has just come, you know, 0:08:51.559 --> 0:08:53.360 we're on the cusp is sort of the next thing 0:08:53.360 --> 0:08:56.400 to happen, and a few people contribute bits and pieces here, 0:08:56.520 --> 0:08:59.319 and some other person puts these things together first there, 0:08:59.400 --> 0:09:01.640 and uh, it's a bit of a mess. Yeah, it's 0:09:01.640 --> 0:09:03.400 a bit of a mess. I think it's fascinating. Also 0:09:03.640 --> 0:09:06.560 how important it is to assign credit for things like 0:09:07.000 --> 0:09:09.720 we have the laser. It's awesome. Are people just fighting 0:09:09.720 --> 0:09:12.439 about the money, like who earns a penny every time 0:09:12.480 --> 0:09:14.640 they make a laser pointer? Or is it about like 0:09:14.679 --> 0:09:18.079 the credit and scientific history? You know, it's it's interesting 0:09:18.080 --> 0:09:20.680 to me how how long and nasty this battle is. 0:09:20.880 --> 0:09:23.880 You mean you wouldn't fight to have that in your tombstone? 0:09:24.320 --> 0:09:28.960 Daniel Whiteson invented the laser? Who would? Oh, I'm definitely 0:09:28.960 --> 0:09:30.800 putting that on my tombstone. True or not? I mean, 0:09:30.840 --> 0:09:32.920 you can put anything you wanted your trimstone. Nobody fact 0:09:33.000 --> 0:09:41.199 checks tombstones. It's like fake news applied to tombstones. I'm 0:09:41.240 --> 0:09:43.600 taking credit for all sorts of stuff in my tombstone. Well, 0:09:43.640 --> 0:09:48.080 let's get into what Daniel is a laser? Right? So 0:09:48.520 --> 0:09:52.160 a laser is different from a flashlight, right, It's not 0:09:52.280 --> 0:09:54.920 just a flashlight with a lens, Okay. A laser is 0:09:54.960 --> 0:09:59.280 something that produces a bunch of light, usually of the 0:09:59.360 --> 0:10:02.480 same color or so, like all a bunch of photons 0:10:02.480 --> 0:10:05.880 of the same energy, and they should all be going 0:10:05.960 --> 0:10:09.079 in the same direction, right, So they're perfectly parallel. Meaning 0:10:09.400 --> 0:10:12.880 if they're like, you know, a tiny distance apart now, 0:10:13.040 --> 0:10:16.360 then a hundred meters away or a kilometer away, or 0:10:16.360 --> 0:10:19.080 a million miles away, they'll still be the same distance apart, 0:10:19.240 --> 0:10:24.839 perfectly parallel, perfectly parallel photons, right, yeah, exactly, So photons 0:10:24.920 --> 0:10:28.920 usually of the same color, shot perfectly parallel, and also 0:10:29.520 --> 0:10:33.120 wiggling the same way. Right. Remember, the photons are waves, 0:10:33.760 --> 0:10:36.040 and they're like all other particles. They're governed by their 0:10:36.040 --> 0:10:38.640 wave equation, and waves wiggle, right, they go up and 0:10:38.640 --> 0:10:40.440 they go down, they go up and they go down. 0:10:40.760 --> 0:10:43.480 And if you have two waves, if they're wiggling in 0:10:43.559 --> 0:10:46.600 opposite directions, one wiggles up the other one wiggles down, 0:10:46.679 --> 0:10:49.720 then they can cancel each other out. Right, So we 0:10:49.760 --> 0:10:51.920 want our photons all wiggling the same way, so they 0:10:51.960 --> 0:10:54.800 all sort of pushed together. It's like folks, on a 0:10:54.880 --> 0:10:57.520 boat rowing at the same time. They all push together 0:10:57.760 --> 0:11:01.199 for constructive interference to make a strong when they hit 0:11:01.280 --> 0:11:04.440 something at the end. You want them to be perfectly synchronized. 0:11:04.480 --> 0:11:08.160 Otherwise they might cancel each other out when they hit something. Yeah, 0:11:08.200 --> 0:11:10.320 that's right, or they might you know, cancel each other 0:11:10.400 --> 0:11:12.600 out part of the way. Um. You know these things, 0:11:12.640 --> 0:11:16.080 these interference effects depend on the phase, and so yeah, 0:11:16.120 --> 0:11:18.800 you want them all pushing in the same direction, um 0:11:18.840 --> 0:11:21.880 at the same time. And so that's what a laser produces. Right. 0:11:21.920 --> 0:11:23.880 That's that's what it means to be a laser. And 0:11:23.880 --> 0:11:26.080 that's an important distinction of people to understand. That's not 0:11:26.200 --> 0:11:29.520 just like a powerful flashlight or of uh flashlights somebody 0:11:29.600 --> 0:11:31.920 put a lens in front of. It's a It's really 0:11:31.960 --> 0:11:34.200 a very different kind of source of light. It's not 0:11:34.280 --> 0:11:37.439 just a really bright light. It's like a perfectly ordered, 0:11:37.800 --> 0:11:40.880 perfectly parallel beams of light. That's right. And there's two 0:11:40.960 --> 0:11:43.280 kinds of lasers. One kind is the kind we're talking 0:11:43.320 --> 0:11:45.840 about where all the photons have the same color, so 0:11:45.880 --> 0:11:48.880 it's monochromatic, right, it's a single color of light, all 0:11:48.880 --> 0:11:51.400 the photons of the same energy, the same color. UM. 0:11:51.520 --> 0:11:53.800 That's the kind that you make to produce beams. You 0:11:53.840 --> 0:11:57.480 can also produce laser pulses, right. These are short bursts, 0:11:57.840 --> 0:12:00.800 and those require having lots of different colors so that 0:12:00.880 --> 0:12:03.720 you add they add up and cancel out in just 0:12:03.760 --> 0:12:06.440 the right way to have a localized burst. And you 0:12:06.480 --> 0:12:08.640 can add up all the different wiggles together to make 0:12:09.200 --> 0:12:11.240 the burst of any shape you want, right. And that's 0:12:11.360 --> 0:12:15.320 different than a flashlight, because a flashlight it's just pumping 0:12:15.320 --> 0:12:19.400 out photons with all kinds of colors and all kinds 0:12:19.400 --> 0:12:22.400 of phases, and they're all out of sync with each other, 0:12:22.440 --> 0:12:24.599 all these photons, that's right. And also they go in 0:12:24.840 --> 0:12:28.920 in all different directions, right. Um, a flashlight usually has 0:12:28.960 --> 0:12:31.560 like a tungsten filament bulb or something, right, and that's 0:12:31.600 --> 0:12:34.160 just glowing and it's sending light in every direction. And 0:12:34.200 --> 0:12:35.800 even if you have it, you know, coming out of 0:12:35.800 --> 0:12:38.560 the front, so it's a little bit um shaped. You know. 0:12:38.600 --> 0:12:40.760 You can take, for example, a flashlight and you can 0:12:40.760 --> 0:12:43.680 point it at the moon, right, and as as you 0:12:43.720 --> 0:12:45.880 get further away from the source of the light, the 0:12:46.040 --> 0:12:49.480 size of the beam grows. Right. Flashlight makes a cone, 0:12:49.720 --> 0:12:52.240 and the cone grows with distance, So you can point 0:12:52.240 --> 0:12:54.320 it to the Moon, and you basically cover the whole 0:12:54.400 --> 0:12:57.559 Moon with your flashlight, because by the time you get 0:12:57.559 --> 0:12:59.640 to the distance of the Moon, the cone is huge. 0:12:59.760 --> 0:13:01.720 Even if you focus it with like a lens and 0:13:01.800 --> 0:13:05.239 try to get them parallel, they won't be perfectly parallel 0:13:05.480 --> 0:13:07.720 exactly right. There's always going to be some spread there. 0:13:08.040 --> 0:13:10.720 Whereas with a laser. If you take a laser and 0:13:10.800 --> 0:13:13.240 you point it at the moon, if you if it's 0:13:13.240 --> 0:13:15.440 a good laser, when it gets there, should have the 0:13:15.440 --> 0:13:17.520 beam should have the same with is when is when 0:13:17.559 --> 0:13:22.160 it left. So that's how that's why lasers are powerful, right, 0:13:22.200 --> 0:13:25.960 because with just a few photons they can go a 0:13:26.080 --> 0:13:29.439 great distance together and so they can transmit that information. 0:13:29.679 --> 0:13:31.520 But they're also kind of in sync so they can 0:13:31.600 --> 0:13:34.360 deliver all that power when they get there. That's right. 0:13:34.800 --> 0:13:36.760 And that example about a laser to the Moon is 0:13:36.800 --> 0:13:39.400 not just like a made up example. I don't know 0:13:39.400 --> 0:13:41.480 if you know, but the astronauts who visited the Moon 0:13:41.600 --> 0:13:44.160 left mirrors on the surface of the Moon so that 0:13:44.200 --> 0:13:46.880 we can bounce lasers off of them and use that 0:13:46.920 --> 0:13:48.920 to measure the distance from the Earth to the Moon. 0:13:50.000 --> 0:13:52.280 I think that's pretty cool. The Earth's beak is selfie. 0:13:52.520 --> 0:13:57.200 You can think we can take a selfie by shooting 0:13:57.200 --> 0:13:59.760 the laser at the moon. And that's right. Even though 0:13:59.760 --> 0:14:02.840 this is decades before the concept of selfies, it was 0:14:03.080 --> 0:14:06.240 it was prescient that way, right. They were forward, forward looking. 0:14:06.320 --> 0:14:09.560 NASA is always looking into the future. NASA invented the selfie. 0:14:10.160 --> 0:14:12.840 We just we just give credit. We just give credit 0:14:12.880 --> 0:14:15.240 to them. They can put it on the Actually the first, 0:14:15.320 --> 0:14:18.160 the first selfie comes from decades and decades before that. 0:14:18.240 --> 0:14:21.680 But but yeah, the first astronomical selfie for sure, first 0:14:21.760 --> 0:14:30.920 laser selfie, that's right. Okay, So that's what the laser is. 0:14:31.000 --> 0:14:34.480 It's like, it's like something that makes light, that shoots 0:14:34.560 --> 0:14:37.760 light that's perfectly in sync and perfectly parallel and that's 0:14:37.760 --> 0:14:41.400 really powerful. Okay, so what why is it called laser? 0:14:41.480 --> 0:14:45.160 Like what what? What does that acronym mean? Light amplified 0:14:45.440 --> 0:14:49.480 by stimulated emission radiation. That's right, let's break that down, right. 0:14:49.520 --> 0:14:52.120 The first one is just light. Okay, so photons are light, 0:14:52.240 --> 0:14:57.680 that's obvious. The last one, the last one is radiation, right, 0:14:58.360 --> 0:15:04.240 and radiation in this case also it just means light. Yeah. 0:15:04.560 --> 0:15:05.960 I think that's because they didn't want to call it 0:15:06.000 --> 0:15:09.400 a laser that would have been more awkward with an 0:15:09.560 --> 0:15:16.720 l So both of those words light and radiation just 0:15:16.800 --> 0:15:19.320 refer to the photons, right, Okay. So it's something that 0:15:19.400 --> 0:15:23.280 makes light, something that makes light and um and it 0:15:23.360 --> 0:15:26.160 makes it in this special way using this process called 0:15:26.320 --> 0:15:30.280 stimulated emission. Okay. And that's the really the guts of 0:15:30.320 --> 0:15:32.760 the laser. That's what's going on inside, is that it's 0:15:32.800 --> 0:15:35.680 a system that creates this stimulated emission. So we should 0:15:35.680 --> 0:15:38.640 dig into that. The A and laser beings amplified, meaning 0:15:39.320 --> 0:15:42.240 you're not just making that use sort of amplifying it somehow. 0:15:42.600 --> 0:15:44.600 That's right. The basic principle of the laser is you 0:15:44.640 --> 0:15:47.320 start with one photon of the color that you want, 0:15:47.680 --> 0:15:50.640 you know, and you amplify use that to use this 0:15:50.720 --> 0:15:52.720 system to multiply you. So I want to start with 0:15:52.760 --> 0:15:55.200 one photon and then you create a chain reaction that 0:15:55.240 --> 0:15:57.960 gives you ten photons, and then a hundred photons, and 0:15:57.960 --> 0:16:01.720 then a thousand photons, etcetera, etcetera. Grows exponentially until you 0:16:01.760 --> 0:16:04.640 have a very very intense beam of photons all the 0:16:04.680 --> 0:16:08.120 same kind. And the key is the stimulated emission. That's 0:16:08.120 --> 0:16:10.880 the thing that basically copies the photon. It says, if 0:16:10.920 --> 0:16:13.680 you have one of the right wavelength or to all 0:16:13.720 --> 0:16:16.000 the right attributes, then I can make more for you. 0:16:16.200 --> 0:16:20.120 That's this process called stimulated emission. Okay, let's get stimulated 0:16:20.200 --> 0:16:36.760 by stimulated emission. But first let's take a quick break. Okay, 0:16:36.800 --> 0:16:40.200 So laser is something that makes light that's all the 0:16:40.280 --> 0:16:46.200 same color, the same wavelength, the same direction, the same wiggle, 0:16:46.720 --> 0:16:49.600 and it's all done by something called stimulated emission. What 0:16:49.640 --> 0:16:51.720 does that mean? Right? So the thing that's doing the 0:16:51.760 --> 0:16:54.680 emission is just an atom, and so you have some 0:16:54.800 --> 0:16:57.080 medium in your laser. Maybe it's a crystal, maybe it's 0:16:57.120 --> 0:16:58.960 a gas that doesn't really matter, but it's a bunch 0:16:58.960 --> 0:17:03.520 of atoms. And atoms can emit light, right, any atom, 0:17:03.720 --> 0:17:05.600 any atom can emit light. Right, you make you get 0:17:05.640 --> 0:17:09.440 things hot and they glow, right, that's something emitting light. 0:17:09.480 --> 0:17:12.920 So if you pump energy into some material, right, it 0:17:12.960 --> 0:17:15.920 will absorb that energy and bring it internally into itself. 0:17:17.000 --> 0:17:19.440 But then sometimes it gets rid of that energy. That's 0:17:19.480 --> 0:17:22.760 called emission, and it turns that energy into light. And 0:17:22.800 --> 0:17:25.560 the way that it does that is it has inside 0:17:25.560 --> 0:17:27.960 it, it it has these electrons. Right, So every atom has 0:17:27.960 --> 0:17:31.720 electrons whizzing around it, and there's electrons have a few 0:17:31.880 --> 0:17:35.120 certain orbits that they can use around the atom. It's 0:17:35.160 --> 0:17:37.879 like a bunch of different energy levels. Electrons can't just 0:17:37.920 --> 0:17:41.320 have any random energy level around it atom. Based on 0:17:41.359 --> 0:17:44.920 the shape of the atom and the configuration of the protons, etcetera. 0:17:45.040 --> 0:17:47.400 There's a few places the electrons are allowed to live, 0:17:47.520 --> 0:17:50.160 so they're called energy levels. And you can imagine sort 0:17:50.160 --> 0:17:52.679 of a ladder of these energy levels. And that's kind 0:17:52.680 --> 0:17:56.840 of related to their wave nature of electrons, right, because 0:17:56.840 --> 0:18:00.000 their waves they can only fit in so many ways 0:18:00.280 --> 0:18:02.840 around the atom. Right, It's sort of related to that, right, 0:18:03.040 --> 0:18:06.000 It's very closely related. Yeah. Um, the reason that there 0:18:06.040 --> 0:18:10.480 are discrete energy levels, right, quantized energy levels, is precisely 0:18:10.520 --> 0:18:13.240 because of those waves and the way the waves fit 0:18:13.280 --> 0:18:15.840 together around the atom. So a simple way to think 0:18:15.880 --> 0:18:18.679 about it is when the electron goes around the atom, 0:18:18.720 --> 0:18:21.240 it's going to do it's wiggling, and you wanted to 0:18:21.280 --> 0:18:23.520 build on itself. You don't want it to cancel itself out, 0:18:23.960 --> 0:18:27.280 and so when it comes around one orbit, you need 0:18:27.359 --> 0:18:29.080 to be in the same place in its wiggle either 0:18:29.119 --> 0:18:31.399 it's wiggling up or it's wiggling down. It has to 0:18:31.480 --> 0:18:35.399 fit a very specific number of wiggles in an orbit. 0:18:35.600 --> 0:18:38.320 You can just do like three and a half that's right. 0:18:38.359 --> 0:18:42.320 It has to wiggle once or twice or three times. Right. 0:18:42.359 --> 0:18:45.040 If it wiggles one and a half times, then it's 0:18:45.040 --> 0:18:47.120 going to get out of sync with itself and eventually 0:18:47.160 --> 0:18:50.159 cancel itself out. So those are not stable solutions. So 0:18:50.160 --> 0:18:53.320 you can't have an electron hanging out and wiggling one 0:18:53.359 --> 0:18:55.399 and a half times around the atom. So each of 0:18:55.400 --> 0:18:57.359 those is a different level. It's not like the Earth 0:18:57.480 --> 0:18:59.760 going around the Sun, like if something moves as a 0:18:59.760 --> 0:19:02.920 little bit, our orbit will increase a little bit. That's 0:19:02.920 --> 0:19:06.520 not how electrons work. They have very specific orbits that 0:19:06.560 --> 0:19:09.320 can fit around the nucleus of the atom. Yeah, that's 0:19:09.359 --> 0:19:13.920 actually a really interesting deep question. Is the Earth's orbit quantized? 0:19:14.440 --> 0:19:17.399 Are there an infinite number of orbits? That's not a 0:19:17.440 --> 0:19:21.480 one with a simple answer. If gravity is not quantum mechanical, 0:19:21.840 --> 0:19:24.119 then you're right, so there's an infinite number of orbits 0:19:24.119 --> 0:19:26.840 the Earth can take. However, if the gravity is quantized, 0:19:27.359 --> 0:19:31.280 then then you're wrong, and there are energy levels around 0:19:31.320 --> 0:19:33.400 the Sun, but those energy levels would be so tiny 0:19:33.440 --> 0:19:35.800 we could probably not even see them anyway. That might 0:19:35.840 --> 0:19:40.320 be the subject of a different podcast. Yeah, exactly. Yeah. 0:19:40.359 --> 0:19:42.440 So the energy, So the electron has these energy levels 0:19:42.440 --> 0:19:44.520 it has on these ladder. This ladder can go up 0:19:44.520 --> 0:19:47.640 and it can go down. Yeah, people use the ladder analogy, right, 0:19:47.680 --> 0:19:49.720 like electrons can be here or it can go up 0:19:49.800 --> 0:19:53.359 a level or another level. Right, It's like very discrete steps. 0:19:54.080 --> 0:19:56.399 And just like with the ladder, what happens when you 0:19:56.440 --> 0:19:58.800 go up a level? Will you It takes some energy 0:19:58.840 --> 0:20:01.320 to do that, right, put some energy into your thigh 0:20:01.359 --> 0:20:03.880 muscle to push you up, and then you're storing more 0:20:04.040 --> 0:20:07.000 energy or you have more gravitational energy because you're higher up. 0:20:07.400 --> 0:20:09.280 The same thing happens with the electron. How does it 0:20:09.280 --> 0:20:12.359 go up a level? It needs to get energy from somewhere, right, 0:20:12.359 --> 0:20:15.040 it needs to get heated up or absorb some light 0:20:15.160 --> 0:20:17.760 or something. So it can go up a level, right, 0:20:18.320 --> 0:20:20.159 and then it can go down a level. And what 0:20:20.160 --> 0:20:22.760 happens when it goes down a level While the energy 0:20:22.960 --> 0:20:25.120 level it was at is fixed and the energy level 0:20:25.200 --> 0:20:27.919 is going to is fixed, so the energy difference between 0:20:27.960 --> 0:20:31.399 them is fixed, meaning every atom has the same levels. 0:20:31.400 --> 0:20:34.840 And if electrons jumped down from one level to the 0:20:34.880 --> 0:20:38.520 lower one. Then they're going to release a photon whose 0:20:38.680 --> 0:20:41.320 energy is exactly the difference between those two levels, right, 0:20:41.400 --> 0:20:45.080 conservation of energy. The electron loses energy, goes down a level, 0:20:45.119 --> 0:20:47.879 and it gives off that missing that extra energy in 0:20:48.000 --> 0:20:50.880 terms of a photon. Okay, so the electron goes down 0:20:50.920 --> 0:20:53.520 a level, it will shoot out a photon with that 0:20:53.680 --> 0:20:56.720 energy that it doesn't need anymore. That's right, exactly. So 0:20:57.040 --> 0:20:59.400 how do you get a bunch of photons of all 0:20:59.440 --> 0:21:01.400 the same color in the same direction. When you get 0:21:01.400 --> 0:21:03.960 a bunch of atoms, You get them all to have 0:21:04.080 --> 0:21:06.720 their electrons up one level, right, You heat them up, 0:21:06.840 --> 0:21:09.520 you pump some energy into them somehow, and then you 0:21:09.520 --> 0:21:11.840 get them to come down all about the same time. 0:21:12.000 --> 0:21:14.560 You get them excited. You get him excited, right, and 0:21:14.560 --> 0:21:17.800 then you get them the big let down. Yeah, all, 0:21:19.280 --> 0:21:22.200 And when they get the let down, that's when they 0:21:22.280 --> 0:21:24.520 give off a photon, and each one will give off 0:21:24.840 --> 0:21:30.359 the same color photon. The photon is determined exactly by 0:21:30.600 --> 0:21:33.200 its energy, which is determined by its wavelength. Right, those 0:21:33.200 --> 0:21:35.320 things things are all connected, right, But they don't all 0:21:35.359 --> 0:21:37.080 in a laser. They don't all give them out at 0:21:37.080 --> 0:21:39.399 the same time, it's it's kind of like how you 0:21:39.440 --> 0:21:42.639 said earlier. You want to cause a chain reaction that 0:21:42.760 --> 0:21:45.560 will make all the atoms in your laser shoot all 0:21:45.560 --> 0:21:49.480 these photons perfectly saying exactly so that chain reaction is key, 0:21:49.640 --> 0:21:52.000 and you can have an atom and you can give 0:21:52.000 --> 0:21:54.600 it energy. So the electron goes up one level and 0:21:54.640 --> 0:21:56.840 then it's happened to just hang out there for a while, right, 0:21:57.320 --> 0:22:00.960 But what happens when another photon just the right energy 0:22:01.040 --> 0:22:03.800 level comes by, Like if you're an electron, you're an 0:22:03.800 --> 0:22:07.280 excited state, um, and there's like a ladders step ladder 0:22:07.320 --> 0:22:10.080 step below you, or you could go down. If a 0:22:10.080 --> 0:22:13.600 photon comes by just that right energy level, it has 0:22:13.680 --> 0:22:16.480