Aritomi and Yuhang

In the beginning of yesterday's recovery of squeezing measurement, we measured LO spectrum with homodyne and found lots of peaks at the low frequency region. We checked the clipping and the centering of beam on homodyne PD. It was fine.

However, since we recognized that the frequency of 24.5Hz comes from scroll pump. And 20Hz comes from clean room fan. The 13.5Hz peak comes from bench horizontal mode. We decide to put back the board wihch is taken away because the demodstration requirement we had on Monday. After that, the measurement of LO spectrum becomes very clean.

Maybe the balance of weight on top of bench helps to remove the bench horizontal mode peak. And the board isolate the sound wave propogates to the mirrors and PDs. These help to remove peaks. But the source of peaks at 16Hz, 18Hz and 33.8Hz are still unknown.