Verification of Calibration

Comparison of calibration method

Normally, the differential length response of the detector is calibrated using one Pcal system, varying the length of only one arm. The KAGRA interferometers, however, have Pcal systems installed at both end stations. They can be used simultaneously to produce either pure differential arm length variations, where the two arms of the interferometer stretch and contract out of phase or pure common arm-length variations, where the arms stretch and contract in phase. Comparing differential and common excitations, enables diagnosing systematic differences between the two arms and quantifying the coupling between common-arm motion and differential-arm motion.