Naoki, Camilla, Wen
The upper mirror of the periscope for FCGS path was reported to be 35%-40% loss in 65076. We re-measured the power on the path using a PD100A instead of a power meter, because it's very difficult to hold it steadily near the periscope. The PDA100A is calibrated at 532 nm at 0 dB gain setting. The output is 193 mV with 0.4 mW of green light. The dark offset is 3.7 mV.
Before swapping the mirror, we measured a couple of points:
| Before periscope | 36.6 mV | 0.070 mW |
| After top periscope mirror | 25.6 mV | 0.046 mW |
| After bottom periscope mirror | 24.8 mV | 0.045 mW |
So the top mirror does transmits 35% power.
After replacing the top mirror, we have
| Before periscope | 36.4 mV | 0.069 mW |
| After top periscope mirror | 36.4 mV | 0.069 mW |
| After bottom periscope mirror | 35.6 mV | 0.067 mW |
| On FCGS REFL PD | 32.2 mV | 0.060 mW |
Now the top periscope mirror is truly a high-reflective mirror.
We also swapped the lens mount and the mirror mount such that the SK beam is not clipped. These paths are also realigned. We noticed that the FCGS power is very low compared to previous results. This might be due to a bad alignment. We'll re-align the green tomorrow.
