To see the possibility of using HAMAMATSU PSD for INPUT mirror oplev, I did the comparison between Thorlabs PSD (with amplification) and HAMAMATSU PSD (without amplification) for INPUT mirror oplev.

The comparison result is shown in the attached figure.

Upper figure: (for INPUT pitch) REF0 is INPUT oplev spectrum with Thorlabs PSD. REF 2 Thorlabs PSD electronic noise after amplification. REF 4 INPUT oplev spectrum with HAMAMATSU 04 PSD. Red line: HAMAMATSU 04PSD electronic noise.

Lower figure: (for INPUT yaw)REF0 is INPUT oplev spectrum with Thorlabs PSD. REF 2 Thorlabs PSD electronic noise after amplification. REF 4 INPUT oplev spectrum with HAMAMATSU 04 PSD. Red line: HAMAMATSU 04PSD electronic noise.

It can be seen that Thorlabs PSD has a bit better SNR. This better SNR is proven to come from the amplification (proved in elog2114).