Michael and Yuhang

We moved IRPS to be very close to the waist position. According to a simulation I have done, this will reduce quite a lot the amplitude noise.

To test if this really solves problem. Firstly, after realigning everything, we got the IRMC spectrum as shown in attached figure 1. Then we gave a high voltage difference of 70V, which is almost the maximum voltage we give for IRPS while CC2 loop is locked. In this case, we got IRMC scanning spectrum as attached figure 2. We computed misalignment to be 4.5%.

Compared with the result we had from elog2424, the LO amplitude noise should be reduced by a factor of ~5. From this result, combined with input mirror feedback, we can completely avoid amplitude noise coupling at low frequency when CC2 loop is closed.