Recently we are investigating HAMAMATSU PSD to be used for Oplev. This is due to the noise increase observed for BS Oplev spectrum, which was pointed out to be caused by PSD.

Last Friday, a similar problem was found also in PR Oplev. As shown in the attached figure 1 and 2, the PR Oplev noise has different noise increase at different time.

I also checked PR Oplev spectrum this Monday, the spectrum became normal as attached figure 3.