Irene, Federico, Eleonora, Yuhang
Turbopump's 603Hz is everywhere.
Fig1-2: acoustic spectrum(fan on and off). From these two figures, we can see the clean room fan brings some narrow and broad peaks. The obvious narrow peaks are 22Hz and 386Hz. We could also see some broaden part around 60-110Hz and 330-470Hz.
Fig3: squeezing and acoustic coherence check. The acoustic coupling is everywhere. Some high and meaningful coherence peaks are 313Hz, 453Hz, 526Hz, 756Hz, 1008Hz, 1524Hz.
Fig4-5: squeezing and homodyne box vibration coherence check. Above around 2kHz, there is almost no coherence. Below 1.6kHz, at 24.5Hz(also harmonic), there is some coherence. And it should come from scroll pump. Also 134Hz, 140Hz, there is coherence. Also 281Hz, which comes from the resonance of the homodyne box. Also 516Hz, 533Hz, 591Hz, 757Hz.
Fig6: squeezing and IR phase shifter coherence check. Resonance around 468Hz gives rise to the noise level of squeezing. Other narrow peaks should come from other vibration sources.
Fig7: squeezing and GR phase shifter coherence check. The resonance of the GR phase shifter affects squeezing less. Maybe this is related to the high Finesse of GRMC.
Fig8-9: horizontal and vertical vibration on the top of the bench and coherence with squeezing noise. Horizontal contains 533Hz, 313Hz, 685Hz. Vertical coupling is not so severe.
Fig10-11: squeezing and rack coherence check. It contains 416Hz, 694Hz, 758Hz(from new spectrum analyzer), 833Hz, 878Hz.
Conclusion:
1. We could see a broad peak at around 9kHz. The peak around 20kHz is not analyzed with enough resolution.
2. The noise of the squeezing part is quite broad. But the acoustic and vibration effects cannot explain all the broad rise of squeezing noise level. There should be other noise sources.
plan:
1. We should check the acoustic spectrum at a higher frequency region.
2. For peaks related to mirror mounts and homodyne box, we should be able to remove it if we float bench. For acoustic noise, we should cover bench.
3. Check homodyne sub-DC spectrum up to 50k.
4. There are broad peaks around 800Hz, 640Hz. We should find out where is it from.
