In two separate tests, a laser carried in a military airplane successfully destroyed airborne missiles this week. Since lasers may save the world some day, io9 takes a closer look at them, and how they're more badass than conventional methods of lighting.
The introductory paragraph is a little misleading. Conventional methods of lighting (or heating, since the laser in the test emitted infrared light, not visible to the human eye) may have destroyed the missile. The problem is, they would have destroyed a lot of other things as well. It doesn't do much good to destroy a bomb if it takes another bomb to do it. The difference between lasers and other types of energy is lasers allow their users to choose a type of energy to emit, and to direct that emission at specific targets.
To get only a certain kind of light, one has to limit the type of materials used to give off said light. Different substances will emit different combinations of wavelengths when burned, or otherwise heated. This is apparent to anyone who through luck, design, or wildly irresponsible guardians, was able to play with fire as a child. After a little while spent tossing things idly into the flames, most people will notice that some things burn white hot, or even blue, others produce a more mellow orange-yellow flame.
Certain scientists – recovering pyromaniacs – have made an entire field of study out of this; spectrum analysis. Analyzing the wavelengths of light given off by astronomical bodies can show scientists what those bodies are made of. The knowledge accumulated by spectrum analysis, in turn, allows engineers to pick which materials they will use in their laser and by extension what kind of wavelengths of light their laser will emit.
To construct a laser, engineers first fill a tube full of the atoms of their choice, and then use either light or heat to drive energy into the tube. When energy is driven into atoms, it pushes the electrons out of their regular orbits and into higher ones. This is an unstable position for an electron, and the it soon returns to its accustomed orbit, shedding the extra energy in the form of a photon. In a laser, that photon will travel around the tube, often knocking other unstable electrons out of their orbits and causing them to shed even more photons.
A good way to picture this is by imagining the electron as one end of a seesaw. Sure, it can move between the up and down position, but it's not very stable when it's up. The energy being driven into the tube of atoms pushes the electrons to the ‘up' position and balances a photon precariously on top of them. Eventually the electron will swing back down into the 'down,' or more stable position, letting its photon roll off and away. That photon will upset other seesaws, causing their photons to tumble off and roll away to upset still other seesaws. Add to that the fact that laser tubes are mirrored on two sides, making the photons ‘bounce off' the walls of the tube and wreak even more havoc, and soon the tube is a roiling mass of photons.
But it isn't quite a laser, yet.
The photons inside the tube travel in every direction. If they were allowed to escape through the sides of the tube, the laser would look a bit like a neon light. If the photons went out through one end of the tube, the light would fan out like the beam of a flashlight. How to turn this riot of photons into an organized march?
The answer is to make one of the mirrored walls half-silvered. Half-silvering is a technique used to produce two-way mirrors, some camera equipment, and lasers. A thin reflective coating is placed on the surface of one of the walls. Depending on the thickness of the coating and the angle of the wall, this coating bounces many of the photons back into the tube, but allows a small percentage of photons through. In our seesaw analogy, it would be like putting holes in one wall, but making them small enough and angling them so that only the photons traveling in a specific direction can get through them.
In this case, the photons that got through were traveling in the direction of a big honking missile, and they disabled it. This marks a huge step forward in the Star Wars program, but will it be enough to make the program workable? There are, after all, a lot of missiles out there. Soon, there may be a lot of lasers out there, too.