Everything you ever wanted to know about solid-state lasers

Georgy Shafeev/Shutterstock

Before you go running out to that hot new club down the street, we need sit down and have an honest talk about lasers and how they work. In the news recently, you may have read that the US Air Force wants to attach lasers to jet fighters.

But how much do you really know about them? You know that cats love thempilots hate them, and in that one scene from Real Genius, Val Kilmer filled a house full of popcorn by cooking it with a laser from outer space. Here’s everything you need to know about lasers.

The word "laser" is actually an acronym that stands for Light Amplification by Stimulated Emission of Radiation, which is probably the reason no one remembers that it’s an acronym. It makes sense, though, once you start to break down the process.

First, I need you to remember your physics 101 class on electrons. These little negative particles travel in orbits around the nucleus of an atom. Apply a little energy, and you can nudge these little guys into a higher orbit. Once you take away that energy, the electron drops to their original orbit, but they release that excess energy as a light photon. (Remember: energy can be neither created nor destroyed. Energy goes in. Light comes out. Kind of.)

Lasers need a particular bit of excitable material and enough energy to get these electrons in that material to a higher energy state. Once all the electrons drop from their excited energy states, they’ll emit photons with the same energy applied to them.

Then, something amazing happens: All of the photons start to travel in the same wavelength. This is called being coherent, and it occurs when the troughs and crests of all the wavelengths come together like marching soldiers. But this still doesn’t explain how something you use to amuse your cat could potentially take down incoming missiles.

An artist's conception of a jet fighter equipped with lasers.

At this point, the effect needs to be amplified, and this gets accomplished with mirrors. Let’s get back to our bit of material. When they get hit with energy, photons start to fly everywhere. Some follow each other, most of them scatter about, but some of them hit other electrons to keep the process going. Place two mirrors facing each other on either side of the material for the photons to bounce off of, and now you have all these photons running around like an epic game of Red Rover. And with each bounce, the mirrors collect a few more photons.

As it turns out, one of these mirrors is only partially reflective. Once the photons gather enough of their photon friends to follow them in their wild run, they pass through the mirror with way more power than before.

The resulting beam concentrates all those protons to move in the same direction, on the same wavelength, and focuses their movement on a very small area. As you can expect, that amount of energy rips through nearly anything in its path, but other factors such as the movement of the plane and the distortion from the atmosphere makes it nearly impossible to keep the laser steady or stable without computers constantly adjusting the beam.

Now go out into society—and impress your friends—feeling confident that you know how lasers work.

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