Cosmic Connections: Lasers in Space!

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Lasers are known for being very uniform in color and very narrow. And pretty.Free for commercial use (via Pixabay)

Cosmic Connections is a series that explores how our experiences here on Earth aren’t so different across the universe.

Lasers are some of the most fantastic inventions to come out of twentieth-century labs. The name itself has been around for long enough that we’ve pretty much forgotten that it’s an acronym – the original word is LASER, for Light Amplification by Stimulated Emission of Radiation. I’m busting out the full name here because the full name is so dang helpful in understanding exactly what a laser is and does: it amplifies light by taking some radiation and…stimulating its emissions.

Okay, so what does that mean?

Here we go. If you energize a bunch of gas (either by heating it, shaking it, shooting light at it, or whatever), the little electrons in the atoms will get excited and move further away from their nuclear parents. Eventually, though, they’ll get bored in the lonesome and slink back down closer to home, in the process emitting some radiation.

It turns out that electrons can’t be any old distance they choose to be away from their nuclei. Due to various and very important (and very much the subject of another article) rules of the quantum mechanical universe, electrons can only exist in fixed, discrete distances around a nucleus. So instead of sliding closer and further away, they jump up and down. This means that when you excite, energize, or stimulate a gas, it will give off light in only a few very specific energies, which correspond to very specific wavelengths.

That’s why lasers have incredibly specific colors: their innards are filled with a uniform gas.

However, lasers have one more trick up their sleeves to make them so…lasery. In addition to the uniform color, they’re also very narrow.  This is achieved by “pumping” the gas with some extra electric fields, causing all the electrons to jump and down in synchronicity and in the same direction.

See? I told you: light amplification by stimulated emission of radiation.

It turns out that nature is perfectly capable of making lasers, too!NASA, ESA, and J. Nichols (University of Leicester)

Now for the space part. We can make lasers here on Earth, and in fact the first lasers operated not at visible wavelengths but in the microwave – they were known as MASERS. No points awarded for guessing what that acronym stands for.

These kinds of microwave lasers are found all over the universe. All it takes is an energy source (and there are a lot of energy sources floating around, like giant stars or supernovas) and a random blobby cold cloud of molecules. The radiation from the bright source blasts into the cloud, exciting the electrons and forcing them temporarily into higher energy levels. The electrons then jump back down in unison and – bingo – maser time.

Of course these astrophysical masers don’t have a fancy tube and electronics, so they don’t get the super-narrow awesomeness we usually associate with lasers, but the fundamental physics is absolutely identical.

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