[Aritomi, Yuhang, Yaochin, Eleonora, Matteo, Raffaele]
First we aligned IR into filter cavity. Current mode matching is around 95.8%.
| Mode | IR transmission |
| TEM00 | 400 |
| HG10 | 112 |
| HG01 | 105 |
| offset | 102 |
Then we succeeded in locking CC2 with filter cavity with new phase shifter. This time CC2 testmass feedback worked well and CC2 correction signal and IRMC reflection became more stable. Gain of testmass feedback is -2.
We measured FDS at 600Hz and CC2 phase noise (Pic.1,2). CC2 demodulation phase is as follows. CC2 error signal is 76mVpp. At high frequency, we had 3dB squeezing, but the spectrum was not clean. Below 100Hz, there was large bump.
| CC2 demodulation phase for SQZ (deg) | CC2 demodulation phase for ASQZ (deg) | |
| FDS | 70 | 100 |
| FIS | 95 |
After this measurement, we found that DC balance of LO was bad. We measured frequency independent squeezing before/after DC balance (Pic.3). After DC balance, squeezing spectrum and squeezing level got better, but still not clean as before.
Then we measured FDS again with/without testmass feedback (Pic.4). Low frequency bump became lower down to 60Hz and it doesn't change with/without testmass feedback. It seems that DC balance improved low frequency bump.
