Figure 2

Figure 2: Scheme of a Michelson interferometer. When the end mirrors of the interferometer arms Mn,e are at rest the length of the arms L is such that the light from the laser gets reflected back entirely (bright port), while at the dark port the reflected waves suffer destructive interference keeping it really dark. If, due to some reason, e.g., because of GWs, the lengths of the arms changed in such a way that their difference was δL, the photodetector at the dark port should measure light intensity I δL Idark(δL) = -02 (1 − cos4π λ-).