Template:Gravitational wave observatory principle
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![](http://upload.wikimedia.org/wikipedia/commons/thumb/0/06/Gravitational_wave_observatory_principle.svg/170px-Gravitational_wave_observatory_principle.svg.png)
Figure 1: A beamsplitter (green line) splits coherent light (from the white box) into two beams which reflect off the mirrors (cyan oblongs); only one outgoing and reflected beam in each arm is shown, and separated for clarity. The reflected beams recombine and an interference pattern is detected (purple circle).
Figure 2: A gravitational wave passing over the left arm (yellow) changes its length and thus the interference pattern.