Alexa, Sheila, Lisa, Evan
Today we looked a bit further into the demodulation issues we've been having with the DRMI sensing matrices (see 14792).
Using the same technique as described in LHO#14792, we measured the response of REFLAIR_A and REFLAIR_B (along with REFL_A) while driving PR2 and SR2.
We ran at 10 W into the IMC, with no ND filter on any of the diodes. Excitations were 131.7 Hz and 6000 counts on PR2, and 183.8 Hz and 6000 counts on SR2. At one point, we also tried exciting PR2 at 211.7 just to make sure our results were the same (and they were).
While monitoring the PSDs of the RF-demodulated diode signals, we tuned the phases as follows:
- RF45 was tuned to minimize the amount of SRCL signal in Q
- RF9 was tuned to minimize the amount of PRCL signal in Q
- We did not retune RF27 or RF135.
The attached plot shows the RF-demodulated diode signals after this retuning. Our conclusions are as follows:
- SRCL and PRCL are nearly orthogonal in REFLAIR_B_RF135.
- For the remaining diodes, SRCL and PRCL are not as orthogonal, but nonetheless cannot both be fully put into the I phase.
The DTT file for this measurement is at /ligo/home/evan.hall/Public/2014/11/REFL_Tuning/REFL_Tuning_Spectra.xml.
Alexa made sure that there was no clipping or any other funny business with REFLAIR_B.
We briefly tried to take a measurement at a lower input power, but could not keep DRMI locked.
For reference, the original demod phases are as follows:
- REFLAIR_A_RF45: 143°
- REFL_A_RF45: −5°
- REFLAIR_A_RF9: 93°
- REFL_A_RF9: 62°
