How Lasers Work

sophisticated heat beam, which we called a laser. Using these lasers, we punch a hole in the protective layer around the Earth, which we scientists call the ozone layer. Slowly but surely, ultra violet rays would pour in, increasing the risk of skin cancer. That is, unless the world pays us a hefty ransom. Joy that was an easy one, you know,

I Yeah, that's true. You know it's one because we sort of obfuscate as to what the topic of the show is going to be when we start, not just time yet you could probably read it before you even sure, and you just don't don't mean it. Yes, well, obviously we're gonna be talking about weather changing technology. Yes, now we're gonna talk about lasers, and this comes from a little Facebook feedback, you be, Nathan had this to say, how do lasers work? How does the lights stay in

a straight line? What makes them different than a beam of light? Well, Nathan, we thought we would tackle this, and in order to explain lasers, we actually have to first talk about atoms. Indeed, you wouldn't necessarily believe it to be so um, you know, maybe not anyway, but yeah, the the science behind lasers is very very tiny on the atomic or molecular level, depending on what kind of laser you're talking about, most of the scientists don't top four ft ten. That's a lot at any rate, the

right right to Jonathan, if you sists. So let's just do a little review on atomic science. This is this is from a high level. So anyone who has taken any kind of science classes where you've talked about atoms, this is going to be very familiar to you. But just just bear with us, because you have to start from somewhere right. Yeah, and and not all of our

listeners are necessarily going to know this. So the atom is comprised of a nucleus, which is at least one proton and usually a pro some protons and some neutrons. Protons being the positively charged sub atomic particles, neutrons being having no charge, and then there are it's surrounded by a cloud of electrons, yes, and the electrons are the

negatively charged particles. So you have with a with a standard atom in its elemental form, you have no net charge because the the protons and electrons cancel one another out. Now the electrons. Uh, it's this gets a little complicated.

We have to kind of simplify things. Imagine that electra ons orbit the nucleus at different shells, Like there's a there's a shell that's a certain distance from the nucleus, and then there's another shell further out, and another shell further out, and only so many electrons can occupy each shell at a single time. Yeah, they really the orbit the nucleus in a way that uh, in which you know, for the more complex types of atoms, you you have

some that are closer to the nucleus than others. They're just not room enough in that orbit for those other electrons to be. And it's funny because you think about it in a three dimensional sense, and it's far more complex than the diagrams we've used to have to make in chemistry class, right with the circles and the larger

circles and the larger circles. But if you think about I mean, these electrons are negatively charged, right right, So that means that they repel one another like repels like. So that's why you can only have so many electrons within that physical space, because they're gonna be pushing against one another as they're rotating as the orbiting I shouldn't

say rotating as they're orbiting the nucleus. M Now here's the interesting thing is that the if you if you inject energy into an atom, what's your what happens is that those electrons will elevate to a higher energy state, so they will actually move further away from the nucleus. If you, if you inject enough energy into an atom, it will lose its electrons, or at least some electrons.

That's how we generate electricity. So but if you if you don't do that much, if you just generate enough where it's the electron has been pushed out to one of the outer energy levels, and then you then remove that that source of energy, the electron will naturally come back down to its ground energy state. But we know about the law of conservation of energy, right, you can't that energy that you injected into the atom. It has

to come back somehow. Well, in this case, when the electron comes back down to its ground state, it emits a photon, which is a light particle. M hm. And you know who had this idea way back in the day, would it be Mr Albert Einstein? Yes, yes, uh you know, of course we have an article about lasers on how Stuff Works dot com. But I wanted to go, um see what Britannica had to say about it, because I

thought that would be a good general explanation for lasers. UM. And it was Albert Einstein who in nineteen sixteen figured that, uh, you know, he he noticed that that adams could release light when they were stimulated by light. UM. And you know it was Rudolph Walter Leidenburg who actually saw it happen. He was he was doing some experiments UM. And for a while, this this phenomenon, it was just sort of

a something that we knew. It wasn't anything that we did something with you, oh, let's go build some lasers. In fact, there's a natural phenomenon that happens, uh that you can you can observe if you're far enough to the north or to the south on the Earth, which are the northern and southern lights of the Aurora borealis

and the Aurora astralis. And the reason for this is that you know, the Earth has a magnetic field, and that magnetic field converges at the north and south poles, the magnetic north and South poles and UH, and sometimes that magnetic field gets disrupted, for example, when there's a solar flare, and sometimes the solar flare will send enough energy to Earth that it it kind of uh will twist the magnetic field will realign earth magnetic field that

tends to dump a lot of energy into the ionosphere, and the particles in the ionosphere they'll this is what happens. The electrons get elevated to a higher energy state when the atoms calm down, essentially they emit photons and we we can see that invisible light. And that's when you know, if you're at far off to the north and you look off and you see these bright flashing lights in the sky and they're all these pretty colors, that's what's happening.

It's actually the same phenomenon that we use to to create a laser UM. So in more to laser history UM, it was Columbia University's Charles H. Towns who decided to try working on atoms at microwave frequencies UM and he actually demonstrated in nineteen fifty three that it could be done. Except he called his a mazer for microwave amplification by the stimulated emission of radiation UM, and he actually got

the nineteen sixty four Nobel Price or physics UM. Also UH Alexander Prokarov and Nikolai Bessov of the PM Lebedev Physical Institute in Moscow, who also we're working on the problem independently, none of it when it seems weird that all these things happen simultaneously, Like we we talked about the development of television. How two different people are credited with the invention of television depending on whom you ask.

Shout out to Philo. Yeah, it's just it's just funny that that UM, and this happens all the time in the development of calculus. But yeah, we weird. Way to go Newton, like, can we have a clear winner please? Anyway, I'm sorry, but yes, I was gonna say so, yes, you you were mentioning the maser that that also is something we should point out that laser itself is an acronym light amplification by stimulated emission of radiation. You can

see why laser was picked over that. Yea, And uh, do you have who made the first true laser um? I do have the first the person who made the first true laser um. Well, if you're talking about Gordon Gould, that is Oh, that wasn't who I have, But go ahead. He is the person who actually got he called it

the laser um. He's the person who filed for the patent. Now, if you're talking about Towns again, he was working with Arthur L. Shallow, who was his brother in law UM, and they were looking at the infrared light and visible light wavelengths. And in December they published a and an issue of Physical Review was published and their paper was in it. UM. But Gordon Gould actually had his patents granted in the nineteen seventies and he's the one who

made most of the money off of it. Because masers had actually been used in atomic clocks and microwave amplifiers, but they really weren't using them for much else. And lasers which use a different wavelengths of light um there, you can use them in different applications, and that's why this was so profitable. Are those the people that you had in Actually, the one I have specifically was a fellow who in nineteen sixty built a laser out of

a synthetic ruby. Ah, you're talking about THEO yeah, Teddy Theodore Mayman. Yes, and uh, that would be the fellow who created the first true laser using a synthetic ruby. Now right now that that's the kind of laser that I think of as being the modern the kind of laser were used today. Although he when I think it's kind of interesting, he used a photographer's flash, Yeah, as a source of stimulation for chromium atoms in a in

a ruby crystal, synthetic ruby crystal. So when you when you're talking about creating a laser, the first step is you have to have some sort of medium that you are going to, uh, you're going to apply energy to in order to excite the atoms within that medium. And I understand that's called a game medium and also sometimes called a lazing medium. So yeah, and you the the process of pouring energy into this is called actually it's called pumping. You pump the lazing medium to generate photons.

That's that. That's a verbie often associate with super soakers, I associated with nikes, these old air nikes. Um. But the uh yeah, so you what you do is you have to generate enough energy within this lazing medium so that you're starting to push the electrons into the higher orbits or the higher energy states, I should say. And what's interest thing is that if the once they the

electrons start coming back down and photons are admitted. If you've if you've arranged the material the right way, the medium the right way, and you have it uh contained properly, those photons when they strike other atoms will excite the atoms they hit, which will then generate their own photons. So, UM, it's not self sustaining. It's not gonna stay that way forever. You're gonna lose energy eventually through various means. But that

that helps you. That's why it's called stimulated emission of radiation. It's it's you stimulate the emission and then the process starts to help sustain itself. UM. Now, with a laser you typically happen to have mirrors on either side of

the lasing medium. So um when the photons start to travel through the medium, And by the way, another interesting thing here is that when a photon hits another atom um and excites the electron, and then the electro and comes back down to its ground state and it emits another photon, that second photon is going to travel in the same direction as the first photon, the one that

hit it the first time. So if you think about it, think of like a series of um of billiard balls rights right physics, and just imagine that you somehow manage to line up those billiard ball balls absolutely perfectly and and they hit exactly the right way, so that when the first billiard ball connects with a second, the second one continues to travel on the straight line from the first one hits the third, third one continues hit going a straight line, hits the fourth, and it just becomes

this chain reaction. Now, because there's a mirror on either end, there's actually a complete mirror on one end and a partial mirror on the other. Um, the photons when they hit the end are reflected back into the medium, and then it continues to create these this flow of photons. Now that partial mirror on the other side allows some photons to pass through, right, and they're all traveling in that one specific direction. It's a very intense, uh, coherent

part of a beam of light. Now, this is the light traveling in a straight direction that Nathan was Yes, Yes, this is it's coherence is the concept we're talking about here. It's it's organized, right, So every photon is moving in the same direction as opposed to a flashlight, which is diffuse. Right. That and for one thing that the flashlight, when the photons are emitted, they're emitted in a more random pattern.

They're not directed like in a laser. And you may even also have a lens that will focus that beam further, depending upon what application you have in mind for this laser. Like a laser pointer doesn't need to to focus the laser in a really intense beam because you're using it just to point stuff out and you don't want to burn a hole through the wall. Right. Yeah, that's that's

the type of laser that I own. I have a red laser at home that I used to h to drive my cats crazy, yes, um, which they very very much enjoy and it also doubles nicely as a laser pointer if you happen to need one. But that's um, you know, they're they're fairly inexpensive because they don't need a lot of um high end parts if you will. Um, yeah, it's and it really depends two on the type of laser.

I mean, they're there are a lot of things that you can change, um about lasers to change a number of things like um, the size of the beam and the color, because it has a lot to do with the medium. Yeah, we should actually point that out. In fact, I'm glad you mentioned that because I forgot to say that. The other interesting thing about a laser is that they are monochromatic. They are all of a single color. Now that color may not even be within the spectrum of

what we can view. It might be not not not with invisible light, because you can have ultra violet lasers, you can have infrared lasers. But the color is dependent mainly upon the the state, the energy state of the electrons, and a lot of that will depend upon what specific medium you are using as your lasing medium. Because the you know, different atoms have different number of electrons, so therefore the the state. The various energy states are going

to be different depending upon which elements you're using. So um, Yeah. For example, a carbon dioxide laser is often used in cutting applications, and it's um, it's it's a it's got a very large wavelength. The wavelength that we were talking about earlier, of course, that's talking about how long the a particular peak and trough of Yeah, that would be a wave. Uh you know that that determines a lot

of different properties of lasers. Red lasers tend to have a wavelength of around six and ninety four nanometers or gnometers, depending on how you prefer it. Um. And remember a nanometer is one billionth of a meter. It's tiny, tiny, tiny, still big compared to the atomic scale. In the atomic scale is about a tenth the size of the nanoscale. So, like we said, depending on the medium, that's what's going to determine kind of the wavelength and therefore the color

of the laser. So if you're using something like argon fluoride for your laser is going to be in the ultraviolet range, which means the wavelength is around ter So that's a tiny, tiny wavelength. The carbon dioxide one is ten six hundred nanometers, so that's quite a long wavelength. And then the stuff that we can see like the typical red laser that might be a helium neon laser, that that's one that can produce a red color and

that's around six and thirty three amnometers in wavelength. So uh, that's to me, that's a really interesting idea is the fact that you know, just by experimenting with different mediums or media I should say not mediums, Um, we've determined that you can create different colors of lasers and and depending and the lasers themselves have different properties that are

valuable in various applications. Yep. Um. And it it's worth noting to um that you mean you could use gases, solids or liquids as a medium for for lasers, and most of the ones we use our gas, um liquids are are the least common from what I understand from my research. But UM, yeah, it's uh, it's funny because

it really the color laser too. You might go on to uh shopping sites where they have geek toys and uh and look at them and go, well, you know, the laser laser pointers like five dollars for a red one, but it's ninety or a hundred fifty dollars for blue or violet or you know what, what is the deal with that? Well? Um, I think part of that is that some are easier to make than others. Um. Part of that is probably the medium to scarcity of the

medium and part of its demand. Um. And I think part of it also is how cool they look and how new they are, because um, now the red lasers red laser pointers have been available for so long. Um, you know, they're pretty common. I mean you could get I I picked mine up as a matter of fact, in the grocery store in the pet section. Um. But yeah, if you want to, if you want to violate laser, they're harder to find. Um. Yeah, I haven't been out

as long, and they're kind of expensive. Hear, Mace Window had to drop three Corelian Freighters in order to get his lightsaber. You know, I almost mentioned lightsabers and whether or not we were growing our own crystals or not for this, and then I thought, I'll wait and see if Jonathan mentions it. You can just listen to our lightsaber podcast if you want to. That was that was a fun one. But yeah, but yeah, it had these these are these wavelengths, these lasers and different wavelengths are

great for different kinds of applications. True, because I know you you were, you know, talking about Blu ray players Blu ray versus DVD. Yeah, yeah, okay, so DVD players. Um, the old DVD players used or still us really red lasers to read information off of a DVD. And the way this basically works is think of the DVD. It's got a it's got a layer on the DVD that has information that's recorded and essentially little pits. These little

pits are read as ones and zeros. What happens is a laser will hit the pit or the blank space, because that's also information. It's just saying it's a zero rather than one. Essentially, I'm oversimplifying. Yes, yes, it's it's complicated. But and there's a reflective surface that's beneath that layer. So the laser hits the pit or the smooth space hits the reflective surface, bounces back towards a cent sore.

Sincere I'm talking about lack lasers and sin sores, I don't know what the heck's happened in me this morning, guys, anyway, So the laser hits the pit, hits the reflective service, bounces back hits the sensor. The sensor detects whether you know what kind of element was on the DVD. That gets translated into digital information, which then eventually becomes the

picture on your television screen. So with a red laser, you remember, the red lasers wavelength is around six and thirty three ninometers, So there's a certain amount of information you could fit on a DVD single layer DVD UH that you cannot exceed because the red lasers only able to detect something of a size that its wavelength can

hit and bounce back from. Like if the pits were smaller, the wavelength wouldn't even detect it because the wavelength would be larger than the the actual element it was trying

to detect. Well, Blu ray players use a blue laser, and blue lasers have a a smaller wavelength, shorter wavelength, their wavelength around footers, So essentially you can cram more information onto a blu ray disc because the wavelength is smaller, and UH, you the path the pattern on the DVD if you will, well, I mean, the disc itself is doesn't have to be as large for the laser to read it, so you can pack more information on there because the blue lazer has no trouble reading it at

a smaller size. Exactly. Yeah, if you if you want to think of it in h here's another weird way. Think of it like a wall that's covered in in in white and black dots. Alright, but the white and black dots are maybe like a six inches in diameter. So you're using a flashlight, and the flashlight is shooting is has a has a circle of about six inches in diameter from the distance that you're at the wall, and you you you count the number of dots as

you swipe the flashlight left and right across the wall. Well, then let's say that you've got another wall that has dots that are two inches in diameter, and you've got a flashlight and you've got a light that's two inches in diameter. It's you're going to be able to count way more dots on that wall than you could with the ones that were six inches in diameter. That's the same concept here. So it's interesting to me that just by switching to a different kind of laser, we've been

able to cram more information in a storage medium. It's a really neat idea. And we talked recently about light Peak, which is now called Thunderbolt, at least as far as Apple products because it's apparently got an exclusivity deal with Apple. Um. But you we talked about light Peak a couple of episodes ago, and light Peak uses um infrared Uh uh yeah,

infrared lasers instead of visible spectrum lasers. But it's same sort of concept here is that it's using that to shoot information sation from a chip to a device or vice versa. Uh. The digital information gets translated into a series of flashes of this laser, which get picked up

by another sensor and then transmitted back into digital information. Now, um, there's something else I wanted to talk about that's related but not exactly on topic, but it's it's very recent and it's really cool, so I thought I would mention it. It's okay with you? Please do have you heard about this? Uh? This article that was published in the February issue of Science. Is it about an anti laser? It is. I knew about uncle laser, but I don't know anti laser very well.

Please all right, let in the interesting full full disclosure. I have not read this article. I don't know anything about it, but are one of our science editors, Alice and louder Milk. She mentioned it to me this morning and I thought, oh, I need to look that up, and I just didn't have the time to do it. So please tell me what is this? Well, I got my information not from that particular article, but from the

Yale Daily News, an article by Antonio Woodford. Uh. And and it's relevant to Yale because it's Yale physicists who came up with this idea. It's it actually is a device that absorbs light instead of emitting light. So that's why people are calling at the anti laser. That isn't it really what it is? A laser, you know, stimulates atoms to to generate light UM and this absorbs light,

so they're calling it an anti lazer. But it's really called and And the reason you'll you'll understand in the second why people are calling at the anti laser because it's a lot more fun to say than coherent perfect absorber. Yeah, I know it's a scientific name. So anyway, um, Uh, physicists Douglas Stone and we cow um, we're working on a device that absorbs light and basically instead of using a game medium, UH, it uses an absorbing medium instead.

So it's basically a chamber like a laser UM and if you shoot two light beams into the two and two ends both ends of the device, it will absorb around four of infrared light. UM. And basically what happened UH is Stone was trying to describe how lasers work much as we are trying to do to someone else and realize, you know what, I bet you could reverse

this process and have an absorb light. So as an experiment, he decided to work on this and UM, basically you know, it was successful in in creating a device that if you um, you know, shown a uh an infrared light into it, it would absorb the light. And you say, okay, well that's a need experiment. But what can you do with it? We remember when we were talking just a moment ago about transmitting information via light peak or you know the blue ray and DVD players. You're transmitting information

over the laser. UM. You can use uh the coherent perfect absorber I'm sorry, anti laser. Yeah, it's not really what it's called, but it's so much more fun. Yes, it is. UM. You can use it to detect pollutants in the air. And because it can basically by by shining the light through the pollutants and having it in uh end up in the coherent perfect absorber. Um. You know,

you you can pick up information from that. Also, you can use it for wireless communications, transmitting information basically from one point to the other with a light on one end and the absorber on the other end. Um. So they said. Also it could be used in optical computer chips. So that will give you another article to write, and maybe this time they won't change the name at the

last minute. I have another possible use for it. Okay, you could use it to coat your car and then the cops can't tell how fast you're going using a laser speed detector. I'm betting that that's not gonna work. It's like a stealth car. It's brilliant. I'll make a billion. No one steal that. But yeah, they can use it in they think they can use in an optical computer chips by change to to change light into electricity. Um.

So it's you know, it's not just an experiment. It's something they think they can uh you know, put into products in the future and Uh, it's kind of a neat idea. I would never have thought to do that. Um. But then again, in n I might not have seen use for a laser either. So I thought we might also talk a little bit about potential hazards with lasers, because here's the thing is that when you have this intense beam of light, that's a lot of energy concentrated

into a relatively small space. Yes, and that energy can sometimes be dangerous, yes, especially if it's particularly concentrated. So there are different levels of laser classifications that UM that will essentially will tell you like how dangerous they can be. Uh. For example, a class one laser, Uh, they they aren't really that hazardous at all, But it goes from class

one to class four. There's a couple of little sub levels in there too, like there's a class you know, there's like a class three M and that kind of thing. But up to the class four laser, you're talking about high powered lasers, which are dangerous to look at and are also they can you know, create, they could they

could burn things they can, including you or other objects. Um. And interestingly, a lot of this has to do with the wavelength again, So lasers that have a wavelength between around eighty to three and fifty nenometers can if you were to get hit in the eyes with them, they can actually create an inflammation of the cornea UM. And then slightly higher than that, up to four nmeters you're talking about possibly creating cataracts UM. And then higher than

that you're talking about retinal burn. Uh. And then uh you're talking about corneal burn if you get a little higher than that. I mean, it's dangerous stuff, especially around the eyes. And that's part of the reason why you may have heard stories about UM Pilots and airlines concerned with the possibility of people shining lasers into the cockpits

of airplanes, and uh, then this is the thing. I mean, there have been thousands of incidents reported of pilots uh noticing that someone's trying to uh direct a laser into the cockpit. It's not to burn the person necessarily, but perhaps blind them or caused some other uh problem during takeoff or landing, and those, of course are the most critical times of an when an airplane is is traveling. So uh, yeah, lasers are are I mean, they're kind of cool to play with, but yes, when you hear

the warning don't shine this into your eye. Take that to heart. Yeah, and don't shine it in anyone else's eye, right, Yeah, don't shine it in any eyes. No eyes get get shown in. Yeah. I have the feeling that lot of people who are are trying to shine lasers into airplanes are are just pooling around, um and aren't necessarily trying to hurt anyone. But yeah, that's that's not a fun prank to pull on someone. I should also say I

said three M, and that's not right. There is a class three three R and three B. Oh, there's it's an R and a B R. Yeah, because our article is a little outdated, there's been a reclassification of the laser system. So actually I need to go in and update our article. I just noticed as I was looking, I was like, wait a minute, I know that there

was a reclassification of the laser system. Uh. Yeah, there's a class to M, but there's no three M. There's three R and three B. But at any rate, Yeah, the higher you go in general, the more dangerous the laser is to your health and safety. Um. Now, we're probably gonna find lots of other cool uses for lasers. We've used lasers to do everything from uh, studying things at the atomic level to studying things at the cosmic level.

So it's an incredibly useful tool. And it's really amazing that Einstein was able to come up with essentially what was the basis of what what all lasers work on? Way back in in nineteen six And you know, there was no way at the time, no real practical way at the time to build anything that would prove that his theory was correct. So it took several decades before we were able to build something that actually said, hey,

you know what, he seems to know something about this. Well, you know, he he was kind of ahead of his time in a lot of ways. Well it's all relative. H So that wraps up this discussion. If you do want to learn more about lasers, we have several articles on the site that relate to lasers and including how lasers work, but also our articles on everything from CD players which also use lasers, to DVD, Blu Ray, UM

and tons of other content. And it is a really fascinating technology and I recommend looking into it if you've ever been curious. UM. Also, there's the the amazing documentary film real genius. There's a bunch of students making a laser. Okay, that that's that's not a documentary. It's actually a comedy from the Eight starring fel Kilmer. But yeah, I I recommend all those things because that movie is hilarious. And

with that, we're gonna wrap up this discussion. If you would like to tell us about how you plan to use a laser to dominate the Earth or any other sort of suggestions of topics that we can tackle, you can let us know on Twitter or Facebook. Are handled there is tech Stuff hs W, or you can email us. That address is tech stuff at tell stuff works dot com and Chris and I will talk to you again really soon. Pu pu laser for Mora on this and thousands of other topics. Is it how stuff works dot com.

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