Okay, leaving behind controversy, philosophy, and such for a moment, I'm going to approach something simpler, and something I know a bit about. Tonight, I'm going to write about how a laser works.
There's one basic thing that you have to understand about Quantum Mechanics in order to understand lasers. You see, in quantum systems, you often have discrete energy levels: the electron in the hydrogen atom can have -13.2 units of energy (we'll call it eV... don't worry about what that unit means, just know it's a unit of energy that physicists use when dealing with atoms and stuff) or -3.4 eV, but it can't be between those two energy levels. The difference between these two energy levels is 9.8 eV. So if you've got a hydrogen atom, and its electron is sitting in the lower energy level, it needs to get exactly 9.8 eV from... somewhere... if it's gonna go up to the higher level. Maybe you shine a light on your atom, and it takes 9.8 eV out of the light. But there's a catch: it turns out that light comes in discrete packets (that's the idea of a "photon," really), and the amount of energy in a photon is directly related to the frequency/wavelength of the light. So you need to choose just the right color of light (in this case, it turns out that it's ultraviolet light) to give your electron the energy it needs. If you do that, your electron absorbs a photon of light to jump up to the higher energy level, and you have an event that is called "stimulated absorption."
At the same time, if your electron is sitting in the higher energy level, and a photon with that same 9.8 eV happens to come by, the photon can actually do the opposite, it can make the electron jump from the higher energy level to the lower one, and in the process, the electron emits another 9.8 eV photon, identical to the first. So, you start with one photon and an "excited" atom (one with its electron in the higher energy level), and you end up with two identical photons and a non-excited atom. This is called "stimulated emission," and it happens at the same rate as stimulated absorption. So if you had, say, 1,000 atoms, and 500 of them started in the lower energy level, and 500 in the higher energy level, and you shined a light on all of them, you'd end up with your excited atoms and your non-excited atoms sort of switching places, at exactly the same rate, so that you always have 500 atoms in each energy level. Also, because every stimulated absorption event takes a photon (its energy is used up in exciting the atom), and every stimulated emission event creates a new photon, the number of photons remains constant.
But what if we could put all 1,000 atoms in the excited state? Well, then, when you shine your light on them, they all emit light instead of absorbing it... so, when all is said and done, you get an extra 1,000 photons. And each extra photon emitted is identical to the photon that stimulated its emission.
Okay, let's make this bigger. Instead of 1,000 atoms, let's have a reasonable number... like a mole of atoms. Then we put them all in the excited state. Then we wait. Eventually, with so many atoms around, something called "spontaneous emission" is going to happen, which basically means that an atom can't just hold onto extra energy forever, at random the electron is going to go back to the lowest energy level and emit a photon at exactly the right wavelength. Then that photon is going to go flying... until it runs into an atom. And with 10^23 around, that won't take long. And when that happens, since the atom it runs into is also in the excited state, you're going to have stimulated emission, and then you'll have two identical photons flying together inside your collection of atoms ("gain medium" is the technical term). And then your two photons run into another atom. And another. Soon, your single photon has become millions and billions of identical photons, all flying together in a big, concentrated beam of light. Eventually, the beam leaves the gain medium. But you put a mirror at the end of your gain medium, so your beam bounces back and goes through your trillions and quintillions of atoms again, and as it does so, your beam gets even bigger. It exits the gain medium again. But you put another mirror there, so your beam bounces back and forth, and you get even more atoms emitting light, until you have this awesome beam of laser light. At this point you might ask how you ever get the light out from this pair of mirrors, and there are a few ways, maybe the easiest is that you make one of the mirrors so that it only reflects most of the light (say 90%), and the rest goes through. But, regardless, you have a laser: a beam of coherent light, made up of identical photons in a concentrated beam, made by amplifying just a tiny little seed through stimulated emission by millions of atoms (incidentally, LASER is an acronym: Light Amplification by Stimulated Emission of Radiation).
And this brings me back to the title. The only tricky part is that you have to get at least the majority of your atoms in the excited state. But, in general, things don't like sitting in the excited state. So you have to find a way of "pumping" your gain medium: putting the atoms in the excited state. Some things are easier to pump than others, and that's one of the reasons that certain types of lasers are easier to find than others. But every material has quantum transitions, so if you work hard enough, pump it hard enough, you could put more atoms of any material in the excited state, and then it would "lase" (because with a noun like "laser," it's just so convenient to verb that noun). Doesn't mean you'll have a good laser (if your gain medium is opaque, or if air is opaque at the wavelength of the light it emits, you might not have much of a beam), but at least inside your gain medium, you can make lasing happen.
There is a logical fulfillment of this fact: the Jello Laser. Yes, that's right. You can make a laser from any transparent material, and it's usually convenient to work with solids (because, you know, you can put mirrors around them and they keep a nice shape and stuff), so people made a laser from Jello. The Jello laser (bonus points in Utah if it's green, I'm sure).
Title: Attributed to Theodore Maiman, who demonstrated the first laser.
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