Aritomi and Yuhang

There was END mirror pitch/yaw coupling problem found in AA sensing matrix, as reported in elog2165. Besides, it was found the END mirror driving from coil/magnets has already been not clean, as reported in elog2173.

So we decide to find a good driving matrix for END mirror. Before doing that, the check about if the END mirror PSD is sensing well the pitch/yaw was done.

The method is to excite yaw of END mirror and check the response of  signals in pitch/yaw channel relative to this excitation. If the sensing is not good, the resonant peak will go from yaw channel to pitch channel.

The test result is attached. By comparing the resonant peak at 1.58Hz, the sensing coupling was found to be around only 1%. This means that sensing coupling of oplev is not a problem.