Michael and Yuhang

We have optimized in-vacuum Faraday rotator and achieved a reduction of in-vacuum propagation losses from ~15% to ~11% as reported in elog 2727 and 2729.

To confirm this lower losses, we locked filter cavity and used BAB to measure it again. Especially, the measurement when chamber opened was done with a HR mirror just after dichroic. We made BAB reaching input mirror this time.

After earthquake and alignment of GR beam, we can still find IR resonance for filter cavity. The achieved filter cavity IR transmission was ~300. This indicates a mode matching level of (300-100)/(550-100) = 44%. Since we don't need IR to be resonant inside filter cavity to measure in-vacuum propagation losses, we didn't optimized mode matching yesterday. The AOM frequency was found to be 110.037371 MHz to have IR resonant for filter cavity.

We made mistake of not removing the CC pick-off mirror at the beginning. After removing the pick-off mirror, we measured filter cavity injection and reflection BAB power as Fig. 1 and Fig. 2. During the measurement, we took care to try to center beam on the sensor of power meter. This implies that the in-vacuum propagation losses are 11.6%. This is in agreement with elog 2729.