To buy or make a new PSD, the gain of PSD is an important and necessary information. Therefore, I measured it as following.

The wavelength of the used laser is 635nm. I set this wavelength for the laser power meter. Then I checked the 635nm laser power used in PR chamber. It was 0.28mW.

Then I measured the PR PSD sum voltage with oscilloscope, which is 11.4V.

Therefore,the high gain PSD should have gain of 40.7 V/mW.

I forgot to measure the size of PSD, but it seems to be 1 inch. I will confirm.