Design study of the KAGRA output mode cleaner

Most second-generation gravitational-wave detectors employ an optical resonator called an output mode cleaner (OMC), which filters out junk light from the signal and the reference light, before it reaches the detection photodiode located at the asymmetric port of the large-scale interferometer. The optical parameters of the OMC should be carefully chosen to satisfy the requirements to filter out unwanted light whilst transmitting the gravitational-wave signal. We use the simulation program FINESSE and realistic mirror phase maps that have the same surface quality as the KAGRA test masses to find out a proper design of the KAGRA OMC.