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.
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