LASERS and SPACE and SCIENCE!

Yesterday I got an email regarding internships at the Mines Center for Space Resources, for which I am hopelessly underqualified but for which I am going to apply anyway. One of them involves working with Laser Induced Breakdown Spectroscopy. I've talked before about how neat lasers are, and I've mentioned that some time I should blog about spectroscopy. This is the perfect opportunity to do so!

Spectroscopy is a method by which we can tell the chemical composition of something based on the light it emits. Which is really neat, because all we have from outer space is light-- well, electromagnetic radiation, actually, but it's the same thing. It's not like we can send a probe to a star to test its chemical composition. We have a hard enough time sending probes to Mars! But using spectroscopy, we can look at the light a star-- or any celestial object-- emits (or reflects), and we can see what it is made of. That, to me, is freaking COOL.

To understand how it work, you have to have a little bit of quantum mechanics. That might seem scary, but it's really not that bad. Imagine the simplest atom you can, a hydrogen atom. It has one proton, which makes up the nucleus, and one electron, which orbits that-- sort of, but there's no reason to equivocate on that topic today. The electron, it turns out, can have different energy levels. What's interesting is that they are distinct-- it's like if your car could go zero, five, ten, and twenty miles per hour, but nothing in between. You would be stopped, and then without transition, you would be moving. These energy states are called "quantized" because they have distinct, specific quantities. This is why the word "quantum" came to be used for subatomic physics.

Anyway, you have one electron, and it can have several different, distinct energy states. If the atom is excited-- that is, energy is introduced, and the atom absorbs it-- the electron will pop up to one of the higher levels. But an atom does not like to stay excited for long, so soon enough, the electron will pop back down to a lower level, and when it does that, it emits a photon-- that is, a light carrying particle. It gets rid of that extra energy in the form of electromagnetic radiation. And because those energy levels are quantized, so are those emissions of light. If you were in your quantized car, as described above, and you wanted to drop from twenty miles per hour to zero, you would have to get rid of a lot more energy than if you went from twenty to ten. So it is with the electron. The more energy it needs to emit to get back to a lower level, the higher frequency light it will emit.

The electromagnetic spectrum is huge. It goes all the way from radio waves, whose wavelengths can be as long as football fields, to gamma radiation, which is so high energy it's extremely bad for you. Right in the middle, a tiny sliver makes up the visible spectrum of light. At the 'top' with the highest energy is blue-- a little bit more energy, and it goes into ultraviolet light, which we can't see without help. At the 'bottom' with the lowest energy (and longest wavelength) is red-- a little bit less energy, and it goes into infrared, which again we can't see without help. Between the two are the colors of the rainbow. When we see colorless light, we are seeing a blend of those wavelengths.

So our hydrogen atom's electron is bouncing around, as quantum particles are wont to do, and it is emitting photons whenever it jumps down. It turns out that four of those emissions are in the visible light spectrum. When we view light emitted from excited hydrogen, we see four distinct lines. And it turns out that no other element has those exact lines-- in fact, every element has its own set of distinct spectral lines. We can even see it if the electrons are jumping up instead of down-- they absorb light, so there will be a dark line in that element's signature places. Now we have a means of telling what kind of particles emitted the light we are seeing-- or, in the case of absorption lines, what the light bounced off before it reached us.

How cool is that? We can look at the light from a star millions of light years away, and we can do a little math, and say for certain what that star is made of. SO COOL.

Now, a little bit about Laser Induced Breakdown Spectroscopy. It's a lot easier to do this sort of thing when you have a burning gas then when you have a solid-- everything emits radiation, but it's not usually in the visible spectrum. So what do we do, if we want our Mars rover to be able to tell what something is made of? We either give it a big fancy chemical lab that can do all sorts of tests... or we give it a high-powered laser. Curiosity, which is on its way to Mars currently, has such a laser. When it lands, it will be able to point that laser at a rock and vaporize a tiny part of it, energizing those atoms in the process, and from there, it can read the spectral lines. It doesn't have to pick up rocks or do complicated chemical tests. It just zaps a rock, which can be however far away, and analyzes it from there.  How cool is that?

I love my school-- I have an opportunity, albeit and unlikely one, to work with this really cool science that I am so fascinated by.

Also, science is AWESOME.

LASERS

You know what is really cool? LASERS.

I put that in all caps for two reasons. One, not everyone knows (or remembers) that the word "laser" was originally an acronym. It stood for Light Amplification by Stimulated Emission of Radiation. Of course, it has become a word-- everyone knows what a laser is, and it's perfectly fine, grammatically, to write it just like that. I write it in all caps, mostly, because lasers are FREAKING COOL.

Everyone has seen, probably even used, a laser. Laser pointers are common technology (though when I was a kid and desperately wanted one, they were at least $50, I checked), CDs and DVDs are read by laser, barcodes are scanned by laser-- lasers are everywhere. The laser sight on a sniper rifle is such a well known piece of technology that a red dot appearing on someone in a movie is an instant source of tension-- that person is going to be shot!

The scientific uses for lasers are even cooler. The distance from the earth to the moon is measured by bouncing a laser off a reflector left by one of the Apollo missions. Lasers are used in microscopes to image extremely small things with great accuracy. Lasers can cut more precisely than any mechanical process. Lasers can perform surgery where no incision is necessary. They're used in spectroscopy, which is a really cool concept on its own.

So how do they work? Fairly simply, actually. You pump light into a medium that will amplify it, and then focus it out one end as a beam. Of course, it's not as easy as it sounds. You have to find the right medium so the wavelength that you want is amplified, you have to use an external power source, and so on. But really: create a tube, with mirrors on both ends, so light will reflect. Fill it with a gain medium-- it could be as simple as glass or neon, like a neon light, mixed with helium-- and then introduce a light source. For some, it could be an electrical pulse, like the helium-neon mix. For others it's a light, or a chemical reaction. It depends on what you're using as a gain medium. Make sure that one of the end mirrors is partially transparent, so the amplified light can go somewhere, and you've got a laser. Many will then put a cap on the end so that the light can only go out through a small hole, making the beam small and focused.

So, one of the really cool things about studying physics at this school is that there are a lot of opportunities to play with lasers. All of the labs on the top floor of the physics building have warnings posted on the doors about lasers. And we have some really, really cool lasers. We've got one setup that's doing microscopy-- that is using a laser as a microscope-- that literally counts photons, yielding a much clearer picture than other systems that amplify to that degree. They've got one that can give a 3 dimensional image of a fly's brain. But the coolest one is the one doing something unexpected.

They created a setup that focuses a beam in four dimensions-- that is, in the three spatial dimensions, and also in time. If you're not used to thinking of time as a dimension that's going to either sound nonsensical or extremely simple. In practice it is neither; this was quite an accomplishment. So they did what any good physicist would do with a brand new, very cool laser: they pointed it at stuff. One of the things they pointed it at was glass. Glass is an interesting thing-- it is structurally the same in all directions, because it doesn't have any sort of crystallization. It's kind of an amorphous blob, really. So, one would expect that, when carving things into it with lasers, the direction the laser was moving wouldn't matter-- the whole area touched by the laser is affected the same way. Generally, that's true. Not with this one. With this one, they get one kind of mark when moving to the left, and an entirely different kind of mark moving to the right. The conclusion they came to: their laser is somehow tiled in TIME. One side of the laser is hitting the glass slightly before the other. And they do not know why. So now there's a senior design project trying to take pictures of this phenomenon. And succeeding. At taking pictures of LASERS.

My school is awesome.