A particularly challenging task in operating a gravitational wave detector is to extract the information about the relative arm length fluctuations from the interferometer’s output port.
This is because gravitational wave signals are encoded in the output beam as phase fluctuations on the order of 10−12 radians.
To extract this information GEO600 implemented a new readout technique, the so-called DC readout, simultaneously with the LIGO detectors. As expected this new readout technique gave a modest increase to the detectors’ sensitivities, among some other technical advantages.
Journal of Physics: Conference Series 228 (2010) 012013