[Marc Eisenmann, Satoru Takano, Yuta Michimura]

We lowered the PD gain for TMS Spol PD by a factor of 10, and turned on two whitening stages for Spol and Ppol PDs, for both Xend and Yend.
TMS polarization monitor PDs are not limited by ADC noise any more, and are sensitve to 1e-8 rad/rtHz level.

What we did:
  - Lowered PD gains from 30 dB to 10 dB for IRSPOL PDs for both TMSX and TMSY, as they were saturating after PRFPMI lock (klog#30892)
  - Turned on analog whitening filters and digital anti-whitening filters one by one to see how many stages are necessary to reduce ADC noise. We confirmed that 2 stages are enough (See Attachment #1 for X and Attachment #2 for Y). Spectra for Y somehow have more structures than those for X.
  - Calibrated measured spectra into polarization rotation angle using the factor described in klog #30885, but 130 smaller to take into account of power difference between single arm lock and PRFPMI lock, and another 10 times smaller for IRSPOL_PDA1 to take into account of the PD gain change. See Attachment #3 and Attachment #4 for the original data in counts for X and Y, respectively, and Attachment #5 and Attachment #6 for the calibrated data for X and Y, respectively.
  - Attachment #7 and Attachment #8 are the photos of the whitening filter switch after the work for X and Y, respectively.

Summary of PD whitening situations (same for TRX and TRY):
  IR_PDA1: 0 dB, no whitening gain, no whitening filters
  IRSPOL_PDA1: 10 dB, no whitening gain, 2-stage whitening filter
  IRPPOL_PDA1: 30 dB, no whitening gain, 2-stage whitening filter

Next:
  - Re-calibrate after the power up
  - Tune whitening for IR_PDA1