Bouncing Balls for a Random Laser
Lasers are often thought of as these exact beams of light that precisely travel in a straight line, but this is not always the case, like with random lasers. All modern lasers work by having a lasing material which produces light between two mirrors, so the emitted light passes through the material many times, which causes more light to be emitted. Often these mirrors are aligned to produce a straight, coherent beam, but random lasers instead project light out in all directions thanks to tiny grains.
The grains in a random laser are essentially mirrors that have been embedded in a lasing medium. Previous attempts to create such random lasers have used such small grains that they are hard to control and susceptible to temperature changes. Now a group of researchers have built a random laser on top of a subwoofer with large grains, roughly one millimeter in diameter. These grains you would normally expect to just sink in the medium, and not have enough distance between them to make a laser. That is where the subwoofer comes in as it precisely vibrates the grains, throwing them into suspension.
The precision the subwoofer offers also allows the frequency of the emitted light to be controlled. The frequency of the light is mathematically limited by the distance between two grains or mirrors. Not only can the frequency be shifted though, but a laser chord can be made whereby two frequencies of light are produced.