Aritomi. Yaochin and Yuhang

We set two PDs outside the PR chamber(attached figure 1), where we have the reference of two IR beams and two GR beams. The set two PDs are used to monitor two IR beams.

Mainly they have two functions:

1. Monitor the power (leakage from PBS before and after in-vacuum FI) injected into the filter cavity. Since we have the problem of IR transmission fluctuation, we want to see if this fluctuation also presents in the input beam. The problem can be found in this entry 1710. We just temporarily monitor this leakage power and the result is shown in the attached figure 2.

2. Use as a reference for the adjustment of in-vacuum FI.