Scientists and engineers at Yale University have just created an anti-laser, a device which absorbs light. Instead of shooting energy out of a tube, it takes energy into a tube. Instead of creating light, it creates darkness. How does it work?
Lasers start out in a tube that is mirrored on both sides. When energy is forced into the tube, the material inside gets excited. The electrons in the atoms of the material jump up a level, and then fall back down. When they do, they emit a photon, which starts traveling around the tube. It bounces off the mirrors on both sides, getting in phase with all the other protons in the tube. Generally, the mirror on one side of the tube is only half-silvered, so eventually the photons find an opening and march out in a directional, single-wavelength beam of light.
Once the light is out of the laser, it's hard to darken it once more. The material it hits doesn't absorb it fully, and so it bounces off, allowing us to see it and allowing our cats to chase it. Scientists at Yale University wanted to create a device that would be able to fully absorb a laser beam.
The device is a small tube of silicon. When two lasers are shot into the tube, the tube traps the light and bounces it around. Enough bounces through the silicon, and the laser light is completely absorbed, leaving patches of complete darkness. The particular device made at Yale was fine-tuned to absorbe only a specific wavelength of light. Any change in the wavelength - the color of the laser - and it loses its ability to absorb. However, the team that designed it believe that it won't be much trouble to adjust it so it works across a larger spectrum.
The anti-laser may be very useful in computing, since it can function as an on/off switch as fast as light can travel through it. Unfortunately, it can't be much use as a shield from lasers. The absorbtion of the energy from the laser heats the anti-laser up considerably. Those who carried it may not get bisected by laser weapons, but they would get fried by their own shields. Perhaps they could carry it with oven mitts.