Optical layout of the squeezed-light enhanced gravitational wave detector GEO600, which consists of the conventional GEO600 observatory and the additional squeezed-light source.
The observatory has two singly folded arms with a total optical length of 2400 m. By means of control loops, the central Michelson interferometer is operated on a so-called dark fringe condition, such that almost of all the light is back-reflected towards the input. A power-recycling mirror (MPR) then leads to a resonant enhancement of the circulating light power at the beam splitter. Similar to this power-recycling technique, a partially transmissive signal-recycling mirror (MSR) is installed to further resonantly enhance the GW-induced signal at the interferometer's output. This combination of power- and signal recycling is called dual recycling.
A gravitational wave passing from most directions will shorten one arm, while the length of the perpendicularly orientated arm is increased, and vice versa in the next half-cycle of a passing wave, producing a periodic power change of the output light that is detected by a photo diode.
BS: 48/52 beam splitter
MFe/MFn: far interferometer end mirrors (east/north)
MCe/MCn: central interferometer mirrors
All interferometer optics are situated in a vacuum system and suspended by multi-stage pendulums.