How Does Laser Interferometry Work?
In essence, the system employed by LIGO consists of suspended weights that are free to move horizontally. A passing gravitational wave would change the distance between the weights, first in one arm, then in the other arm, which is arranged at a right ang le to the first. This distance is measured by a laser beam that is split between the two arms, multiplied many times by passing back and forth between the mirrored surfaces of the hanging weights, then recombined at a photodetector.
