[Aso, Ushiba]
Abstract:
We tested BPC on PR3 by using PR2 and IMMT2.
Both were working but transmitted light power and POP 90 signals decreased: alignment became bad.
Then, we tested BPC for both PR2 and PR3 again with PR3 ADS instead of IMMT2 but not succeeded yet.
Detail:
We tested BPC but not successful.
Followings are the summary we did today.
BPC on PR3 by using PR2 without BPC on PR2:
As reported in klog24747, BPC on both PR2 and PR3 seemed to take a lot of time, so we tested BPC on PR3 instead of PR2.
Figure 1 shows the time series data of PR3 BPC error signals when moving PR2.
We know transmission power becomes better when PR3 moving in + pitch direction but unfortunately PR3 BPC error signals becomes large when moving PR2 in + pitch direction.
So, BPC on PR3 by using PR2 doesn't seem to work well for obtaining better PRFPMI alignment.
BPC on PR3 by using IMMT1 without BPC on PR2:
Same as PR2, this control doesn't seem to work well for obtaining good alignment PRFPMI becaouse of the same reason of PR2 case.
BPC on PR2 and PR3 at the same time with PR3 ADS instead of IMMT2:
Aso-san pinted out it would be difficult to center the beam on PR2 and PR3 at the same time if we do not move PR3.
So, we tested BPC on PR2 and PR3 with PR3 ADS instead of IMMT2 ADS.
We used POP90 for ADS signals and dither frequencies are almost same as that with GRX during the initial alignment.
Figure 2 shows the spectra and relative phase between LO and signals just before demodulation.
Though we can see the peaks at both 30.25 (yaw) and 46.1 Hz (pitch) in POP90 signals, coherence at 30.25 Hz is very low and relative phase cvcannot be measured.
We are not so sure the reason but we proceeded pitch ADS because we thought pitch is more serious in the current interferometer.
Figure 3 shows the setting of PR3 ADS for PRMI and it seems working well.
Then, we closed BPC on PR2 by using IMMT2, BPC on PR3 by using PR2, and ADS for PRMI by using PR3 at the same time.
Figure 4 shows the time series of trans power, POP90, PR3 oplev, and BPC error and feedback,
Though BPC on PR2 and PR3 ADS seems working well, BPC on PR3 doesn't seem working well even though we flipped the sign of feedback several times.
Currently we don't have any further good idea for the alignment of PRFPMI.
