Pew Pew Lasers

high tech stuff today. Actually, I'm gonna look at a topic that we first addressed way back in two thousand and eleven with the episode how Lasers Work. That's when Chris Pallette, my original co host, and I sat down and we talked about a little bit of the history of lasers and how they actually operate. But I thought it would be better to revisit this, explain it again, kind of take a different approach to it. Um. So, lasers are awesome and they can do tons of different stuff. Right.

We can do everything from having a little laser pointer to amuse ourselves and our pets, to having a laser element inside optical drive so that we can read information that's been stored on a disc. Two communications satellites, to propelling spacecraft to cutting steel. There's all sorts of things we can do with lasers. Oh, we can threaten our enemies. We can tie them up and put them on a slab and then slowly have a laser creep upward and then laugh maniacally as we expect Mr Bond to die.

We can do all that sort of stuff with lasers. So we're gonna talk about what they are, what they can do, their history, and maybe some cool trivia about lasers as well, and laser related stuff. So let's get to it now. First of all, what is the technical definition of a laser? Well, laser is an acronym that means that it's a word that's made up of the initials of other words, right, so it stands for light amplification by stimulated emission of radiation. But for most of

us that doesn't really clear things up. That just raises other questions like what do they mean by stimulated emission of radiation? And how do you amplify light? So I'm gonna go in talk about all of that kind of stuff because it's really fascinating and involves a lot of science and technology, two things I love to talk about. The third thing, obviously being Chaucer's Canterbury tails one that applicated with the shoulder at SUTA, but that does not

really fit with lasers. They didn't have the lasers tail, so we're gonna skip Canterbury Tails for this episode. Now, a laser is a device that produces a very narrow beam of light, and these beams are monochromatic. That means they are single colors see single wavelength. That's a very specific wavelength of light for each laser and us a specific color. So we perceive different wavelengths of light as

different colors of light. So if you think of your roy g BIV, that is actually a a spectrum literally a spectrum of colors. That's also a spectrum of wavelengths, with red being the longest wavelength and violet being the shortest wavelength in the visible spectrum. Uh, the wavelength of light depends entirely on the amount of energy electrons release

within the laser itself. So electrons release energy and in the form of photons or light particles, and the color of laser you get depends upon the amount of energy those electrons are releasing, and the amount of energy they release is dependent upon the type of atoms that they are connected to, because it all has to do with orbits of electrons around nuclei. More on that in a second. So the light is also coherent. Now, that does not mean it is able to hold a conversation and make

salient points. It's not that kind of coherent. It means that the light is made up of organized photons. Organized botons in this case means that they're all traveling the same pattern of wavelength that are all in the same page as it were. If you look at wavelength, if you were to draw a series of waves, they would all be lined up exactly, so all the crests and the troughs would be lined up along the same points. At any point along the wavelength, they would match entirely.

So that that is what we mean by coherent. It's what helps keep the light organized and moving in that specific direction you wanted to. And the light is also directional. That means the beam is tight and concentrated and remains so over great distances. You don't get a lot of uh light diverging from that that pathway, and some lasers are able to project for miles and miles, like hundreds of thousands of miles in some cases or uh without having any kind of degradation of the beam, which is

kind of cool. I mean, it's amazingly cool. Now you contrast that with something like a flashlight. Flashlights have a beam that spreads out as it travels outward from its source, it diffuses, so it's different from a laser. It doesn't have the coherence that a laser would have. Um this is typical of most light sources. You don't find lasers in nature. Lasers are something that we have caused to happen because of the natural laws. If it weren't for

the natural laws, lasers wouldn't work. Obviously, we didn't create that out of whole cloth. But it doesn't spontaneously happen in nature because you have to have very specific parameter set up in order to generate a laser beam. Now, to understand why it works the way it does, it helps to know how light works, and a light behaves

both as a wave and a particle. But for this bit of the explanation, we're mostly concerned with wave physics, even though we'll be talking about photons, the basic unit of light, the basic particle of light. A lot in this episode. So a light source gifts off waves of light, and different colors of light have different wavelengths. Like I said, uh, you know, those red wavelengths are longer than the orange ones. Infrared waves are even longer, Ultra violet are even shorter

than violet. So you've got that that different spectrum of wavelengths there. When you get down to that violet, you're really looking at the shortest wavelengths that we can perceive before it just becomes invisible to us. So again, ultra violet, we can't see that um Certain classes and dungeons and dragons different They can see ultraviolet light, not the rest of us. So these waves travel typically out of phase

from each other from normal light sources. So again, if you were to chart those wavelengths, the crests and valleys would of each individual photon wouldn't match up right, like the crest of one might be matched with the valley of another or somewhere else along its wavelength. They wouldn't be moving in phase, they'd be out of phase. So lasers all line up those light waves at the same way so that they are in phase. And that's what

we mean when we say coherent. That the various photons are all in phase with one another, and the way you generate lasers makes this happen. Uh, it's kind of cool. We'll talk about that again a little bit later. But all the photons in the beam have unified wave fronts, so they're all moving in exactly the same wavelength a exactly the same time. Now, to understand how all of this works, it takes. It takes a looking at atoms. We have to go back to basic science. So let's

take a look at an atom. Now. Back in the day when I was in school, atoms were depicted as being kind of like the orbits of planets, where you would have a nucleus in the center, kind of like the sun, and electrons would orbit a neat little circles around at specific distances from the nucleus. As it turns out, things aren't quite so neat and simple. Atrons are in an electron cloud that are around the nucleus. It is impossible to say with complete certainty, Uh, where an electron

is at any given moment. You know, you can know a position of an electron, but not it's direction or vice versa with complete certainty. Heisenberg's and certainty principles is a fun thing. But you know, when you have a basic atom and you haven't added any energy to the atom, it's and it's ground state energy level. That's when it's just you know, kind of chilling. Atoms are always in motion. Uh. You only get atoms in no motion at all at absolute zero, when you're at zero kelvin. That is when

you have zero atomic movement. But otherwise, atoms are always in motion, even in solid objects, they're just not moving a lot. When you add energy to atoms, they move more. They start to get energized. When you energize atoms enough, you can boost them to an excited level. Now, typically you do this by applying energy like heat, light or electricity to the atom. Uh, Whereas if you want to excite me, you just say, hey, they might be giants is coming to town. You want to go see them?

And I mean like, yeah, totally. So you've got atom which consists of that nucleus, and you've got the electron cloud around it. When you apply energy, it causes the electrons to move to a higher orbit around that nucleus. Again, since we're talking about a cloud and not just a simple orbit circle, you can think of it as meaning the electrons move a little further away from the nucleus. If you add enough energy, you can strip electrons away from the atom entirely. This will create a charged UH

atom because you will now have an ion. It's gonna have a pause a net positive charge because you're gonna have protons there and you've pulled away some of the electrons, so you've taken some of that balance out. UH. If you add enough electric enough energy, I was about to say electro steve a really energy. Electricity is one form of energy you could add to the ADAM in order to do this. But if you didn't add that much, like if you had it enough to excite the electrons

but not strip them away from the nucleus. When you remove that source of energy, the electrons will move back down to their ground state. They do not quote unquote want to be at that excited level. They have a ground state that they are naturally inclined to be at. But they've absorbed energy. So in order to move back down to their normal energy level, they have to give up some of the energy that they've absorbed, and they

do this through emitting a photon. That basic unit of light, and once they emit that photon, that's what allows them to move back to their ground energy state because they no longer have that excess energy inside of themselves. So you can think of it as almost being like the elect run is too full, like it's eaten too much, and then it has little belchy belch or something it

manages to emit some part of that energy. It is absorbed, and now it's feeling more like its old self again, and then you can just boost it back up again if you want to. So photons are admitted this way through in lasers, but that's not the only way we generate photons like there are very specific ways of doing this in all sorts of applications, and many of them are pretty basic. Like your incandescent lightbulb uses the same principle.

You run an electric current through some wire a filament, typically in a vacuum sealed tube a bulb, and running the electric current causes the filament to heat up because it has resistance to electrical current, so some of that electricity gets converted over into heat. As this heats up, it excites the atoms within that filament, and as that energy source moves through it allows those electrons to come back down the the atoms begin to emit photons, and

then you get this glow. In the case of light bulbs, the glow creates the light you would have from an incandescent bulb. You could also see the same thing with heating elements, Like if you were to look inside a toaster and you see that orange glow, Well, that orange glow is coming from the heating elements that have had their atoms excited. The electrons got boosted to a higher energy level and then they came down and started releasing photons. So it's not just lasers that do this, but lasers

take advantage of it in a very specific way. That's pretty cool. Now, that's just what's going on with the physics side of things. I haven't yet explained how this really works with a laser. So a laser uses this principle to create those narrow beams of light. And here's how they do it. First, you need what is called a lazing medium, a laser medium. This is the stuff

that you're going to use to excite. You know, you're gonna excite the atoms in this stuff so that it generates the wavelength of light that you want, and so the type of stuff you use that's going to determine the type of atoms that are present, which in turn determines the energy levels of the electrons, which in turn determines what color light you're gonna get through the lasing medium. All of this is dependent upon, ultimately the source of

the lazing medium, Like what is that material? The lasing medium acts like an amplifier, only this is for optics rather than for acoustics. So some people call the lasing medium the gain medium or the source of optical gain because it's like a microphone gain setting, it is amplifying a signal. Then this case, it's amplifying light, not amplifying sound. Uh. The gain in this case is that stimulated mission the photons I was talking about, and the emission is stimulated

through an interesting series of events. You start by initially adding energy to the lasing medium, and then the photons that emits end up stimulating other atoms inside the lasing medium that have already been excited, and then you get a steady stream of photons that create your laser beam. But first you have to add energy into the system. You do this from what is called a pump source

because you are pumping energy into the lazing medium. So basically, you pump energy into this medium, you excite some atoms, the those excited atoms start to emit photons. Those photons will start to h hit other stimulated atoms and that's where you get this um stimulated emission. So there are lots of different types of lasing media. So, for example,

there are certain crystals that can serve as a medium. Uh, the earliest lasers were ruby lasers, so you would get a ruby crystal and that would be your lasing medium. You would usually in introduce some impurities. It's called doping. You add some impurities to the material in order to make this a more efficient lasing medium. Usually it's some ions of some sort um and that helps when you're

actually getting to the part of generating a laser. Those are specifically solid state lasers, the ones that use crystals. You're using a solid lasing medium. But there are other ones as well. There's some that use glasses, some that use gases, including reactive gases like chlorine and florine. Those are specific types of gas lasers that are called xemer lasers. You have semiconductor lasers, which produce, in the grand scheme

of things, fairly weak lasers. But they also are fairly inexpensive to produce, and those are the ones that we use in things like CD players, DVD players, Blu ray players, that kind of stuff. They tend to be semiconductor lasers. They're easy to mass produce, they're less expensive, and they aren't so powerful as to cause problems. You don't need a CD player laser that could burn a hole through the surface of the Earth. That would be ridiculous. You

can also get liquid medium lasers. These are liquids that have various organic dyes special organic dyes d y e s that will allow for this stimulated emission of light amplified light. Now, the pump is some sort of energy transfer that you use to excite those atoms in the first place, so that they'll emit those initial photons when the electrons calm the heck down. Laser pumps are some

form of external source of energy. Typically they supply energy in the form of either electricity or light, but there are other means of pumping a lazing medium with energy to create lasers. Light and electricity are the two most common ones, but they are not the only kinds. There's some that use chemical reactions. There's some that even use nuclear reactions, which I think is taking in a little far if you're asking me, uh, that's me mostly being

tongue in cheek. But again, most of the lasers that we would encounter throughout our day, those are generated either through light or through electricity stimulating the lasing medium. So, for example, most most early lasers were using some form of arc or flash lamp to stimulate that initial reaction within the atoms of lazing medium, like a crystal rod. Uh. So, you got your crystal rod with a few impurities in it that you have specifically placed in there. You have

doped this crystal rod. You would wrap a light source around this thing, usually within some sort of mirrored chamber, and you would flash light impulses against the lasing medium, and this would actually excite atoms within the medium, which would then give off photons. Now, if there were no way for you to keep this reaction going, it would be such a small emission of photons that you probably wouldn't even be able to tell. You wouldn't even it

wouldn't be visible to you. However, by tricking it you can totally make it visible. So you typically would use these mirrors to reflect light back into the lasing medium. That includes photons that were admitted during that initial flash, and that's what allows you to create a cascade effect

and create a laser. Generally speaking, you would probably use mirrors that would allow the election of any wavelengths of light that were shorter than the laser's wavelength would be, and allow the transference of light that is longer, wavelengths longer than the laser's wavelength that you want. The reason for that is that if you were to trap all the light within the chamber, you could cause things to

heat up and create what's called thermal lensing. The actual change in temperature would create a lens effect that would end up affecting the ability of a laser to be directional and coherent. And obviously, if that's your intent, you don't want that to happen. So, yeah, Thermal lensing occurs when a sample absorbs energy from a laser beam, it heats up, it creates this refractive lens that causes beam divergence.

That's not what you want with a laser. Typically, I mean, you might want to design a system that creates that splits a beam, but that's different from beam divergence. You want that beam to be nice and tight. Uh, typically or your your average laser applications. So let's let's imagine that we're building a laser and we start with a rod made out of ruby. I was gonna say that you could have a ruby rod, but we all know that he is busy with Corbin Dallas trying to save

the universe. Shout out to any of you guys out there who understand what that reference means. So you've got ruby rod, and you've got a flash tube that is probably wrapped around the ruby rod, but at least as shining can shine on the ruby rod, and you can use the flash tube out of like a camera. In fact, the earliest lasers were using camera flashbulbs as the source of light to start this reaction. It's not like it's

something super high tech. It's actually pretty cool. And you've got a mirrored chamber that surrounds the whole thing on the on either end of the rod. So think of the rod is like a cylinder. You have put a silvered mirror on either end. One side is a pure silvered mirror, so it just reflects light. The other one is a partially silvered mirror, meaning that it can allow

some light to pass through. Specifically, you want to design it so it allows the wavelength of the laser light to pass through, but doesn't allow any other light to pass through. Uh, you turn on the flash tube. This shines bright light onto the rod, which causes some of

the atoms in the rod to excite. Then as those electrons move back down from their excited stage back to the ground level stage, they release photons, and with enough energy pumped into the medium, you end up with a larger population of atoms that are in an excited state then there are atoms in the ground state. When you reach that point, it is called a population inversion because you've inverted the relationship between a sited atoms and ground

state atoms. Typically, you would have more ground state atoms than excited ones. Once you're able to flip that balance, you can create this cascading effect that I've been talking about. So you've got more excited atoms than you have ground energy level atoms inside of this lasing medium. At that point, they started giving off photons, and this is pretty cool. What happens next is photons from some of those first UH atoms that had been excited and they were calming down.

If you like, they'll go out and they'll hit other excited atoms. So these are atoms that I've already had their energy levels boosted by that flashbulb. The photon from the first atom, the one that excited then calmed down, has just the right amount of energy to cause the electron in an excited atom to come back down to

its ground state and release a another photon. So what happens is the atom that it it connects with will absorb the photon, then it will emit the photon and emit a second photon as its own electron comes down an energy level. So you get two photons emitted, the initial one that you shot the atom with and then the one that that atom produced itself. So this is what it's called light amplification. Right, you have amplified the light.

You started with one photon. Now you have two photons and they're moving in phase with one another because well because of quantum physics, but I don't want to get into that too much. So you get this light amplification through that process. Now that you have the light amplification. You might as well say, like, well, what are we calling this? This whole process where a photon can cause another atom to admit a photon, that's the stimulated emission.

You might think stimulated emission was when you turned on the flash bulb. That's not technically correct. The stimulated emission part technically comes from these initial atoms that release photons, and those cause this chain reaction in the lasing medium. So this can happen over and over and over again. Right, You're not really the atoms aren't losing any matter in this. It's just a process of electrons being boosted up to an energy level and then coming back down again, so

they're releasing energy. They're not losing anything in this. It's just a transfer of energy and really a transformation of it from one form of light to another. So it's fascinating to me that this is something that not only works, but that people were able to figure out would work um. It's it's so far into quantum physics and optics and photonics that I am amazed that people figured us out. In fact, they figured it out way back at the

beginning of the twentieth century. It would take the middle of the twentieth century before anyone built a working laser, but they figured out the physics of it decades ahead of time, and that still blows my mind to this day. Then again, I'm also the guy who can't figure out which remote control controls the TV versus the audio system. So what do I know. You get this series of photons being omitted that are all in phase with one another, and they bounce back and forth between these two mirrored

ends of this ruby rod. But some of them can pass through the half silvered or partially silvered end because that it allows for that, and this is the source of the laser beam. The photons that get out through that end become the laser beam, and it's just a steady beam of light that will continue to fire as long as this reaction is allowed to continue. If you remove that source of energy, the pump energy that is allowing this to happen in the first place, it will stop,

right it will. The reaction is not sustaining. It can't just keep on going, and you have to have that external source of energy to maintain it throughout the whole process, otherwise it just goes dark. So that's basically how your standard laser works. Now, if you're using that ruby based laser I was talking about, the wavelength of the laser light could be measured at six hundred and ninety four nanometers. That's how long a wavelength of ruby laser is. Six

which is incredibly tiny. The visible spectrum of light is between four nimes, which would be the violet side, up to seven nimes, which is the red side. So this ruby one is right up there at the top level of what we can see as human beings. Now, you can also have infrared or ultra violet lasers. Obviously those would be invisible to us, but they would still exist and you can still do some pretty cool stuff with it. In fact, uh, infrared lasers are often used to cut

steel for example. Much pretty serious stuff when you think about it. But we'll talk about that more in a little bit Before we get into more about Pepe lasers. Let's take a quick break to thank our sponsor. Now.

According to the company Wicked Lasers, which makes a range of laser products, including ones that are capable of actually burning stuff if you use them, uh, they say that the wavelength of five five nanometers is ideal for brightness compared to other colors that are produced at that same amount of power. So lasers have a couple of different elements to them. There's the wavelength of the laser itself, and then there's the amount of power that you are

able to generate. You measure laser power in in milliwatts typically for the ones that we use uh day to day as consumers. They can go higher than milliwatts, but typically the ones we consumers use are in the milliwatt lage range rather uh. But you you would measure them in watts the same way you would with light bulbs.

But a ten what laser or a fifty watt laser would be much more much brighter than a fifty watt light bulb, because remember a fifty what light bulb is giving out fifty watts of light, but it's it's emitting that in practically all directions, whereas a laser has it very much concentrated in a coherent beam. So a fifty laser would be incredibly bright compared to a fifty watt light bulb. We're mostly talking about milliwatts. So if you have a a certain laser pointer of let's say let's

just say twenty milliwatts. I mean, it's incredibly small, but this is just for the purposes of an example, twenty milliwatt laser pointer, and it's green, which is closer to that five fifty five nanometers in wavelength, and then you've got another one that's read. The green one's gonna appear brighter than the red one, even if they're both emitting the same wattage of laser light, because our visual acuity is closer to that five fifty five nanometer wavelength range.

So violet and blue lasers are slightly less powerful than that, but the greens are the ones that are going to show up the best for their respective amount of power. Obviously, you can pour more power into a laser, and in some cases you can end up with a brighter laser because of it, of course, depending upon whether or not the laser is within the visible spectrum in the first place. It doesn't matter how much power you pour into an

infrared laser. You're never gonna see it. You'll see the results because it will burn through stuff, but you won't see the laser itself. But yeah, it's all it's all about those extra things as well, not just the wavelength, but also the power. So that's really what helps determinal laser strength is the wavelength and the amount of power that it's putting out. Really, how much power are you

putting in and getting out of it? So if I want to use a death laser in order to defeat my arch nemesis who happens to be a British secret spy, and I want to also use another laser to amuse my cat but not turn it into kitty cat flambay, what do I need to do to make sure about that? Well, one is again that wavelength of light. Certain wavelengths are absorbed more readily by a broader variety of substances than

other wavelengths. So if you pick a wavelength that is easily absorbed by lots of different stuff, that is going to transfer energy more readily to your target. So, as it turns out, and for red lasers can really transfer a lot of energy to a broad array of stuff, including steel. That's why carbon dioxide megawatt lasers are used

to cut through stuff like sheets of steel. But other colors are not as easily absorbed by as wide a variety of materials, and so you would really have to pour more energy into the laser in order to get a beam strong enough to start cutting through stuff. So it depends on both how much power you're putting into the laser and the wavelength of the light. Both of those together will determine how strong quote unquote your laser is. Strong isn't really a meaningful term because there are different

ways of measuring laser. It's by how much light it gives off and also how much energy does it transfer to a target. But if you're talking about the energy transferred to a target, those are the two things you have to worry about. The wavelength and the amount of power that it generates. You can use other stuff to help with that too, like lenses. You can use lenses to help maintain a tighter laser for further distances, but

ultimately it's power and wavelength that you're really concerned with. AH. Lasers can be used for all sorts of things, from optical media like DVDs, blue rays, and CD players, to communication systems to massive industrial lasers UH that can cut

through steel like warm butter and they're really nifty. But I thought it might be interesting to learn a little bit more about not just how lasers work, but sort of the the history of lasers as well, right, because there's a ton of different stuff to to talk about. I mean, who figured out how lasers would even be a thing? Like where did that come from? So to trace the history of the laser, you have to look at the scientists whose work provided the foundation for all

the people who followed. So all the scientists and engineers who actually started building lasers in the nineteen fifties, they did this working off of the theoretical work of people who came before them. So one of those people was Max Planck. So Planck was born in eighteen fifty eight in Germany, and his father was a law professor. And when he was a kid, he was really good at study aims stuff. He was really interested in tons of

different things. He was he was a bit of a pollymath, really intelligent and very and very accomplished in several fields, uh including music. And in fact, when he turned seventeen, he had to make the tough decision what was he going to pursue as a care ere Was he going to continue to study science or was he going to

become a musician. And somewhere there's an alternate universe where Plank decided to become a musician instead of a physicist, and in that alternate universe we had totally different types of piano music that Plank would have written. It would have been amazing. But I think we're pretty thankful for his contributions to science. So ultimately, if we were to measure us versus them, I think we get the better

end of the deal. But still, it's really interesting to think that he could have become a musician instead of a physicist. And he's sort of the father of quantum physics, so if he had not gone into study physics, it might have delayed our study of quantum physics as a discipline by at least a decade, potentially more because his work would go on to inspire lots of other heavy thinkers,

including Mr Albert Einstein. So Plank earned his doctorate the same year as Einstein's birth, so Planka's predecessor to Albert Einstein, obviously, and Einstein would take inspiration from several of plans ideas, and one of those was plucks idea that energy could only be emitted and absorbed in discrete amounts. So if you think about it, it's almost more like digital versus analog. If you've listened to me talk about digital audio, you know how digital audio is made up of tiny little

steps of pitch and volume, whereas analog is a continuous wave. Right, digital audio is a bunch of discrete little moments in time, and the number of those moments in time that's your sample rate. The more the higher your sample rate is, the closer this looks to be a continuous line. But it's not really a continuous line. It's tiny little steps in pitch and volume. Well, Planck's point was that energy

is sort of similar it. Ultimately, when you get down to the very very very tiny amounts could only be omitted or absorbed in discrete chunks. It's not continuous, not analog, And this was a revolutionary idea. Einstein would end up looking at this idea and saying this is pretty cool. Um, I'm gonna use this and add on to it, and he created his theory about the photo electric effect. Plank, meanwhile, would end up being awarded the Nobel Prize in Physics

in nineteen eighteen for his his working quantum mechanics. Einstein would similarly be honored several times. It was Einstein who first suggested that Adams might be able to produce photons through stimulated emission. So lasers are somewhat built upon the theories of Einstein himself. He stated that electrons could be stimulated to a mid light of a specific wavelength, which

of course is the very basis of lasers. And Einstein published that theory in nineteen seventeen, so it would be nearly forty years before anyone could actually build something to test out and see if Einstein's theory was of practical application. Uh, but it turns out he was right, which again blows my mind. Forty years before anyone could build something, and he's saying, hey, you know what probably would work. Ah,

I'm oversimplifying it and making light of it. But I am in awe of people who are able to think in these terms, where they're able to work out the basic laws of the universe well before we could ever make any sort of practical attempt to test those ideas. It is phenomenal to me. Now. Granted, I could make up laws of the universe, but they would be completely unsubstantiated and would face old to hold up to any testing in the future. I lack the ability to have

that level of insight into how our universe works. But I do appreciate it in others. So let's flash forward the nineteen fifty one. So we go from nineteen seventeen

to nineteen fifty one. That's when a guy named Charles H. Towns, who worked at Columbia University in New York, was sitting on a park bench, which in itself is not that remarkable, but he came up with an idea of creating a device that could produce microwaves through stimulated emission of radiation, and this idea became the basis of the Mazer m a s E er, which is similar to the laser, but obviously amidst microwaves rather than light. Three years later,

Towns would demonstrate a working maser. So this is nineteen fifty four, not a laser, yet still a mazer. So microwaves are part of the electromagnetic spectrum, but are not considered of light. Right, you've gone beyond infrared at this point. The wavelengths of microwaves are much much, much longer than the wavelengths of light. Towns had actually partnered with a couple of people in order to create this working maser that included Herbert J. Zeiger and a graduate student named

James P. Gordon. They used ammonia as their medium for the mazer, and the wavelength of the microwave was one centimeter. A centimeter is it's it's almost impossible for me to describe how big that is compared to the the waves that are in the nanometer range, the hundreds of nanometers, but it is while centimeter is small to us, it is enormous in the quantum world. So they were able to create this. They were able to build a working

maser using ammonia as their medium. Now in Moscow around the same time, there are a couple of engineers, Nikolai G. Basov and Alexander M. Prokhorov, who were working on building oscillators at the time, and while they were building oscillators, they came up with a method that they thought would work for negative absorption while building these things, and they called it the pumping method, which would become important for future mazers and lasers. In nineteen fifty six, Nicholas Blomberg

in at Harvard develops the first solid state mazer. In September nineteen fifty seven, Towns would sketch out an optical mazer design in a lab notebook. Also in nineteen fifty seven, there was a guy named Gordon Gould who was a grad student at Columbia who wrote down his own ideas for a device that would be similar to a mazer, but he called this one a laser. So this appears to be the first use of the word lasers, the first recorded instance of laser as a word. And Gould

thought ahead and even had his notes notarized. So he had them notarized by a notary, well as a date on it and everything, so that he could prove that he had come up with this notion. He tracked down a notary at a candy shop and the bronx, which is a phenomenal story in my mind. I love the

idea that this is non joke. This really happened. You had a guy come up with what would become a transformative technology, a laser, like the idea of creating a light version of what had already happened, And so he needs it notarized, so he goes to a candy store. It's pretty sweet when you think about it. By nineteen fifty eight, Towns was working with his brother in law, Arthur L. Shallow or Shallow, I guess is the way you would pronounce it sc h A W l O

W Shallow. He was a researcher for Bell Labs, which obviously has played an enormously important role in the development of electronics in general. Together they proposed developing masers that could operate in the infrared and optical parts of the electromagnetic spectrum. And meanwhile, over in Russia, Prokhorov and Basov were also investigating the possibility of developing optical mazers. So the race was on a lot of different people all

trying to create an optical mazer or laser. In April nineteen fifty nine, Gould would apply for patents relating to lasers, and in nineteen sixty Townsend Shallow received a patent for the optical mazer, which they now were calling a laser, and thus the Great Laser Battle began. Only this laser battle wasn't fought with lasers. It was fought over the intellectual property represented by lasers. And this was a legal battle that would stretch for three decades. So an incredible

laser battle really. But the first working laser was built in Malibu, California, in nineteen sixty and almost certain he had nothing to do with plastic surgery, unlike everything else. In Malibu, California, Theodore H. Maiman, who worked at Hughes Research Labs in Malibu, built this first laser. He used a synthetic ruby that was two centimeters long and one centimeter in diameter, and he coated the ends in silver

to make them reflective. He used a photographic flash lamp to pump the lasing materials, so he used the exact same sort of flash bulbs you would find in a cameras flash, which is pretty incredible. And a couple of months later, Hughes Research would hold a press conference to announce that they had developed the first working laser. A few months after that, scientists at IBMS Thomas J. Watson Research Center demonstrated a working uranium laser, which seems like

a massive show of escalation in my mind. Now, at this point the developments would come really fast and furious, not like the film series within Diesel, but I mean they were just laser development after laser development, tons of advances. I'm not going to cover all of them because they're way too many, but I'll cover some of the big ones. The first helium neon laser debut at the end of nineteen sixty, again at Bell Labs, and it was able to create a one point one five micrometer wavelength of

continuous light, so beyond the range of human vision. It wasn't light that was visible, but it was in the spectrum of light. And in nineteen sixty one companies began to manufacture lasers for the market. This is incredible to me. It what had been only a year since someone had built a working laser, and by the following year people were making them for for sale. Now, granted, they weren't

selling them to average consumers. It's not like John Smith or or or John Q. Public if you prefer it, could walk into the closest laser store in order a laser. These were meant for research and development purposes and not for people who wanted to amuse their cat. It was also meant for some early industrial uses and as it turns out, some early medical uses. So again I'm gonna

jump over some of the incremental developments. It wouldn't make sense for me to cover all of them, and a lot of them I would have to go into even more description about very specific types of lasers which only apply to particular cases and not to others, and that would just make this kind of muddy and and and directionless. But I do want to point out a few really cool moments in history and explain some related topics to lasers as a result, such as what happened in December

of nineteen sixty one. So keep in mind it only been a bit longer than a year since someone had demonstrated a working laser at all. But in December nineteen sixty one, Dr Charles J. Campbell and Charles J. Custer, I'll have Charles Jay's decided that they were going to treat a patient, a medical patient, a human medical patient, using an optical be laser to destroy a retinal tumor.

Now that's incredible. It had been only eighteen months since someone had built the first working laser, and you already had people using it in a medical procedure on a human patient. I suspect that today it would take a bit longer to prove that the methodology being used was safe and efficacious before using it on a human, but it shows how quickly things were moving back then. I think it's pretty incredible that it took less than two years to actually use lasers in a medical and an

actual medical procedure. Now, the mid nineteen sixties would see advances in the field of fiber optics, which, when paired with lasers, allow for long distance communication using light through glass filaments. Now, I've done episodes about fiber optics before, so you can go and look at the Tech Stuff archives and learn more about that. But this still blows my mind too. Just the fact that fiber optics are

a thing that work, it is incredible to me. Meanwhile, Bell Labs would strike again in nineteen seventy two with a laser beam cutter they used to form electronic circuit patterns on ceramic and on June nineteen seventy four, which just for Trivia's sake, is exactly one year to the day before I was born. A barcode scanner, which typically uses lasers. Read the very first product ever registered for real z s using a UPC code and a barcode scanner. The product, by the way, it was a pack of

Wriggley's chewing gum. So how the heck did those barcode scanners work? Because you see him on everything these days and here's where I'm gonna go on a bit of a tangent to talk about bar codes in just a second. And I also just want to mention that, uh, I think it's really cool that, now you know a trivia question that the first product to ever be scanned using a barcode scanner was Wriggley's chewing gum. Important to remember

in case you ever played bar trivia. Now, next, I'm gonna talk all about you PC codes and how they work. But before I jump into that and go way off the rails, let's take another quick break to fake our sponsor. All right, So let's talk about bar codes, which are I agree, tangentially related to lasers. But I've already talked about how lasers work, and I really love how bar codes work because I just think they're kind of cool.

So these are the good old universal product code or UPC code things that you would see on products today at your average store. Uh. They were designed in order to help speed up check out and also make it easier to keep a working inventory of a store. And you can just scan each item and then you use a computer database to match the scan with other information

like what that product is, how much it costs. So the scanner all it needs to do is ident a fi which product you are actually scanning at any given time. That's its only job. It doesn't really have anything to do with how much something costs. That is not necessarily represented in the code itself. There are codes that do have the information in them, but the basic UPC code is really just to tell a system what the product is, and then you have a separate database that links products

to prices. So what would you do if you were a manufacturer and you wanted to put a UPC code on something that you yourself were making, your company was making. Here's the process. You have a company called the Uniform Code Council or you see C, and they are in charge of UPC codes. And to me, the u c C sounds like it should be staffed by shadowy figures in robes. But to be fair, I did watch Hot Fuzz again not too long ago, and that's probably why

I'm thinking that. So let's say you're a manufacturing company and you make a very specific product and you want to get it into stores around the world. And since the earliest implementations of the UPC codes were for grocery stores, Let's say that it's a grocery store products. So let's say you're making a really awesome, tasty, sugary breakfast cereal for kids, and you're calling them Crispy Doos. So you make delicious Crispy doos that are a nutritional part of

a balanced breakfast. You want to sell Crispy doos and grocery stores, so you want to end up selling to grocery stores. Grocery stores will sell the Crispy dues too to their their customers and everyone benefits, presumably assuming that there's enough nutritional value in the Crispy dues to not, you know, turn your customers into goo. So grocery stores love the idea of UPC codes because again, it makes it much easier to ring up products and it makes it very easy to keep track of the stock that

the grocery store has. If they notice that they're selling, you know, eight palettes of Crispy Doos a week, then they might up their order and that's good for you. So it benefits you to get a UBC code on your product. To do that, you would first have to apply for a manufacturer identification number from the u c C. This is almost like a subscription service. You'd have to pay the u c C to get this manufacturer identification number. Uh, the u c C would then issue you this number.

It's a six digit number. And if you look at a UPC code, you'll see that there are twelve digits on the UPC code. So those are the human readable digits, right, that's the thing that you have to type in, and for some reason the scanner is not scanning anything you might type in the code. Well, those first six digits refer to the manufacturer identification number, So all the products from that specific manufact acturer should have those first six numbers the same on all of them because it's it's

unique to the company itself. It doesn't matter what the product is. The next five digits on that UPC code represent the item number, so it's unique to the product. So if you make fourteen different products, each product is going to have its same or its own five digit item code, and it will be different from the other thirteen item codes. So if your company also produced, say Flea colors for kitty cats, the five digits for the fleet colors are going to be different than the five

digits for the Crispy Dues. Which is good because you don't want to mix up your Flea colors with your Crispy Dues. That would be a pr nightmare, and this episode really isn't meant to go into that sort of thing. So that leaves one digit left over. Right, You've got the first six that's the manufacturer I D number, the

next five which is the item number. But you have a single digit leftover of those twelve, so is that for That is called the check digit, and the check digit is meant to give the scanner the opportunity to verify that it has scanned the product properly. And the way you do this is through some pretty ridiculous math.

It's not difficult, it's just tedious. So it's again a verification right to say that, yes, the scan went through properly, because if the math checks out, if you get the answer you're supposed to get, you know that you scanned it properly. And by you, I mean the scanner system is able to verify that a scan went through correctly. So let's take a second to talk about how you arrive at the check digit so you can understand what I mean when you do some ridiculous arithmetic it's not

difficult again, it's just ridiculous. So you've got eleven other digits in the UPC code, and those are what you use to do the arithmetic. First, you take all the numbers, all the digits and the UPC codes that are at odd positions, so not the odd numbers, just in the odd positions. So that would be the position number one, position number three, five, et cetera, up to eleven. Because you have eleven other numbers, you take all of those and you add them together and you get a sum.

So you've got that sum by adding all the odd position numbers together, and you then multiply that by three. Now you look at all the digits that are in even positions, so two, four, six, eight, and ten, you add all of those together. You then take the number you got from all the odd positions multiplied by three, and all the even positions added together, and you add those two numbers to other, and then you take a look at this new number, this monstrosity of a thing.

It's not a huge number, it's just weird that you've got it. And you say, all right, how many more numbers would I have to add to this in order to get a multiple of ten, and as long as the last digit is the same as the number you need to add to your your monstrosity to get a multiple of ten, you're good to go. So this is easier to understand with an example. So here's our UPC code. We've got our crispy doos, and our UPC code happens to be six three nine three eight two zero zero

zero three nine three. Well, that last three is the check digit. That's the number we're supposed to get at the end of all this other nonsense. So we put that aside. We say three is what we're hoping is the outcome. How do we get to that. We take all those odd positioned digits, which would be six and nine and eight, etcetera, etcetera. We add them all up. Technically it's six to zeros and nine. That gets you thirty two. You multiply that number by three, you get

ninety six. So that's your that's your first number. You set that aside. Your ninety six is good to go. Then you take a look at all the even positioned numbers and you add those up. The even position numbers would be a three, A three, two, zero, and another three. That gives you eleven. So now you add the eleven to the ninety six that you arrived at earlier. That gives you a hundred and seven. You look at a hundred and seven and say, how many digits or how much when I need to add to this to make

a multiple of ten? Answers three, because if you had three seven you get a hundred and ten hundred ts multiple of ten. There you go. Three is the number you wanted. Three is the number that's the check digit. You know that you've got the right answer. Now. The way the scanner does this is not by looking at the digits. It's looking at the relationship between the thin uh bars, the gaps between the bars, and how thick

or thin each of those are. Right. So, if you look at a UPC bar code, you're looking at just the bars. You'll see some of the bars are thin, some of the bars are a little thicker, some of the gaps between the bars are thinner or thicker than the others. That relationship of bars to gaps and the thickness of them tells you what the value is of

each of those. And if you're really really wanted to, you could decode to bar code just by sight once you know the basic system of coding, and if you're able to determine what is a narrow versus a wide

bar or gap, because that's very important. So the scanner is looking at the series of bars and gaps and measuring those those widths, and by measuring it, it then is able to match that to a numeric code and verify whether or not it matches that check digit at the end, and if it does, the scan goes through, it gets matched to a product and you're charged however much or your crispy dewes. I'm gonna say it's five

for a BUX, so that's what would pop up. There are variations on these UPC codes like zero suppressed number UPC codes, which is exactly what sounds like. Any number that is a zero that would otherwise appear in the code gets emitted omitted rather not emitted, it's omitted from the code, so it's shorter, makes a shorter barcode. Uh,

But not everyone does this. Only some products have this AH and the manufacturing I D numbers can have a specific meaning as well, depending on what number they start with. So if you're manufacturing I D number starts with a two, it means that it is a random weight prod ducked. And by random weight we mean it's something that doesn't come in a specific uniform size and weight over and over again. So produce. For example, an apple is gonna be its own weight, right, You're not going to get

two apples of the exact same weight. They're not all uniform. Whereas if I go out and buy a box of Crispy DU's, it should be more or less the same as a comparable Crispy Due box. Now if you have if you have different sizes of boxes, then you have different item numbers for each of those different sizes. The item numbers are specific to a very particular instance of

an item. So if I've got a large box of Crispy Us and a small box of Crispy Dues, each of those will have its own five digit item number, and thus the bars that correspond with it will be slightly different as well. Um, by the way, if you wanted to know, like, just as an example, what these bars mean, I'm not gonna go through the encoding of every single number because it would be kind of silly. But let me give you an example. If you want

to represent the number one in a UPC code. The way it would work is that you would use uh first, a black bar that is two units wide, so in other words, you have to look at the most narrow bar on the UPC code that's probably one unit right. You would want a bar that's twice that. With the bar units go up from one to four, so the widest bar will probably be four units wide, the thinness

will probably one unit wide. You need one that's two units wide, followed by a space that is two units wide, followed by another black bar that's two units wide, followed by a space that is one unit wide. So that is the number one in bar code speak, and each of the new roles is encoded in a similar way. Using these bars and gaps of varying widths and reading

them by sight is possible but is not practical. But when you move one of those bars across the scanner, the scanner shoots light, typically red laser light, at the bar code, and then a sensor on the scanner is looking for reflected light and it can detect those bars and gaps based upon the light that gets reflected back at the sensor and as long again as that last bar or that last digit matches up with the math I talked about earlier. It can then ring up the

product and give you the appropriate price for it. Uh So, really, the the interesting thing here is that the laser just

makes this incredibly efficient. I mean, light travels faster than anything else in the world, so it's no surprise that you can just swing one of these barcodes by it a really good clip and still get a really solid scan off of it, because that information is going to the code and back to the scanner at the speed of light, so it's not like you're gonna be moving that fast compared to the scanner um and as long as it's got that good fidelity there, then you're gonna

get a pretty successful scan. That's why you can zoom stuff past that scanner pretty quickly. Now, let's go back to that timeline that we were talking about earlier. By Laser Diode Labs Incorporated had developed a continuous wave semiconductor laser which would make it possible to transmit telephone conversations via optic fiber, which again blows my mind that you could turn something that's acoustic not just into electricity, which is already magic in my mind, but into light signals.

In we got the laser disc, which was the first commercial use of an optical medium, that being something that could be stored on a device that would be read just by laser light alone. Laser discs were a predecessor to other optical based media like compact discs, a K C d s and DVDs and blu rays. The earliest players actually used helium neon laser tubes in order to read the information stored on the discs, but later ones would switch to more affordable infrared laser diodes, so semiconductor

based lasers. And as I said earlier, the semiconductor approach was less powerful and less expensive than other methods of generating lasers, so that helped bring the laser disc price down a little bit, but they were pretty expensive and never really took off. I mean, there were people who loved laser discs, but um they never became as popular

as vhs or later on DVD players. Now later in night, Philips would announce it was working on the compact disc project, which is kind of funny because I always think of CDs as being either a late eighties or early nineties phenomenon, But it's origins date back to the late seventies, and the first actual CD produced would come out in nineteen two. And here's some more trivia for you if you're ever doing that pub trivia. You remember the first thing with

the barcode was Wrigley's Chewing Gum. The first CD to ever be produced was the album fifty Second Street by Billy Joel. That album actually had some pretty good songs on it, uh, including my Life, which would later serve as the original theme song for the Tom Hanks sitcom Bosom Buddies. I guess you could probably tell that I'm I'm patting this episode out a little bit. But this is again useful information if you're ever playing pub trivia.

So if you ever hear what was the first album produced on CD, you now know it's fifty second Street by Billy Joel. In nineteen seventy nine, Gould would finally receive a patent that covered a pretty wide range of laser applications, so that meant that he finally won the

laser battle. You'll remember that in the previous section I talked about how he had applied for a patent but was essentially denied that patent because of a previous application that had taken the intellectual property Gould had created and notarized. So this was the end of a very long battle uh here well, at least as far as who has the legal right to claim the intellectual property of lasers.

But it would be Shallow, who was one of the parties who had filed the other patent back in a couple of decades earlier, three decades earlier, and Blombergen, who had actually received the Nobel Prize in Physics in one for their work in laser spectroscopy. So people were doing well all around in the laser world. In the mid nineteen eighties, research laboratories began to use lasers to manipulate

individual atoms, which is really cool. It opened up a brand new world in quantum uh science as well as just physical science. You may have seen the infamous picture of IBM spelling out its name and individual atoms that use lasers to position them. It's really pretty awesome. And by the late nineteen eighties Gould began to get royalties

for his patents, so better late than never. In seven, Dr Stephen Truckle became the first doctor to use an ex semer laser to perform corrective surgery on a patient's eyes. This method was called the photo refractive care tectomy or pr K surgery. That would start a line of research and development in laser eye surgery in general, with lazic surgery debuting in ninete and I had lazy lazic surgery done just a few years ago. It corrected my vision. Uh.

I talked about it on a podcast. Chris Pallette was on that one too, So you can do a search on tech stuffs archives and hear all about laser eye surgery. And I think if you listen carefully enough you can actually hear Chris Pallette turned green in the episode. He does a lot of unpleasant sounds because it was clear he was not comfortable in that episode. I might have

taken a little extra glee from that. Now, skipping way ahead to two thousand three, that was when researchers from NASA demonstrated that you could power an aircraft using lasers. The aircraft in question weighed just threeleven grams, not kilograms, just grams. It had a balsa would frame and had

a wingspan of one and a half meters. Net used an electric motor that was powered by a photovoltaic cell, so like a solar cell, but in this case it was specifically accepting light from this laser which was firing in an invisible spectrum, so you couldn't see the laser, but you can direct it at the cell that would provide the energy needed to convert it over into electricity

and us propel the aircraft, which pretty cool. And today there are tons of uses of lasers, and some of them are released silly, like you know, they're being sold as cat toys and dog toys at this point, but some are really serious or things that are used in the medical field, for engineering, for industry, and we're looking at the possibility of even using them to propel spacecraft to other star systems, which is a really neat idea.

This is based on the idea of the solar sail, where you have a spacecraft and it has a sale that you can direct light toward, and light has momentum. It's got relativistic momentum, So a photon does not have a lot of momentum by itself, but a stream of photons directed at a surface for long enough does have a physical push to it. And as it turns out, if you build very tiny spacecraft with a decent light sale,

and you use a laser on Earth. You can continuously accelerate that spacecraft over time so that it reaches incre edible speeds. Now that acceleration is going to be at a low rate, so it doesn't speed up immediately, but it will over time get faster and faster and faster.

And in fact, this is what some people are suggesting we do to send spacecraft to the nearest star system are the one that's nearest to our own That would be the Alpha Centauri system, and Proxima B would be the place we would really want to take a look at. That's the the planet around Proximates Centauri that's the closest to our solar system, that is the most earthlike in nature.

And so there are some people saying, why don't we release swarms of tiny spacecraft using these sort of light sales, use lasers to direct them towards the Alpha Centauri system. And because of the incredible speeds they can reach, they can get to the Centauri system within about twenty years. That's incredible because the Centauri systems four light years away. That means it takes four years for light to get there, to hear, so to get there in twenty years using

a physical spacecraft. You're moving at a really good clip. Now, granted at that speed, you're also just zooming by the Centauri system. You're not stopping for tea or anything, but still pretty cool idea that lasers could play an instrumental role in getting us to a different star system, or at least getting our eyes to a different star system. No humans would be traveling on those spacecraft. Well, that about wraps it up for this episode on Pupil Lasers.

I hope you guys enjoyed it. I'll be talking about lots of other cool technology and upcoming episodes, so make sure you stay tuned to that. If you have any suggestions for future episodes, whether it's a topic or a guest I should have on the show, or someone you would love to have as a as a co host for an episode or two, let me know. Send me an email. The address is tech Stuff at how stuff works dot com, or you can drop me a line on social media on Facebook and Twitter. The show's handle

is text stuff h s W as all as. You can also tune into twitch dot tv slash tech stuff on Wednesdays and Fridays to watch me stream the show live, where not only do you get to hear an episode early, you get to hear all the mistakes, you get to banter with me between segments, and you might even hear me tell horrible jokes at the end of an episode. So go to twitch dot tv slash tech stuff to see the schedule and join me there sometime. I'd love to see you until next time. I'll talk to you

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