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Entry  Wed Jan 8 13:01:48 2014, Gabriele, Summary, LSC, Effect of PRC length mismatch on error signals REFL_vs_PRClength.pdf
    Reply  Wed Jan 8 16:08:52 2014, ericq, Summary, LSC, Effect of PRC length mismatch on error signals phaseVlength.pdf
       Reply  Wed Jan 8 19:05:30 2014, Gabriele, Summary, LSC, Effect of PRC length mismatch on error signals as11.pngas55.png
          Reply  Thu Jan 9 17:58:31 2014, ericq, Summary, LSC, Effect of PRC length mismatch on error signals 
             Reply  Fri Jan 10 15:31:07 2014, rana, Summary, LSC, Effect of PRC length mismatch on error signals 
                Reply  Sun Jan 12 09:57:24 2014, Gabriele, Summary, LSC, Effect of PRC length mismatch on error signals 
Message ID: 9544     Entry time: Thu Jan 9 17:58:31 2014     In reply to: 9541     Reply to this: 9546
Author: ericq 
Type: Summary 
Category: LSC 
Subject: Effect of PRC length mismatch on error signals 

[ericq, Gabriele, Manasa]

 We wanted to perform the PRC length measurement today with an AS11 signal, but such a signal didn't exist. So, we have temporarily connected the AS110 PD signal (which is some Thorlabs PD, and not a resonant one) into the REFL11 demod board. 

We then proceeded with the goal of locking the PRC with REFL165. A few parameters that were changed along the way as we aligned and locked things:

  • the XARM gain was increased from 0.4 to 0.5 to help it acquire lock
  • the MICH gain was decreased from -10 to -5 since there was some gain peaking in its servo output
  • the REFL165 demodulation phase was changed from 155 to 122, to place a PRCL excitation entirely within I (we did this while locked on the carrier)

Sadly, in the end, we couldn't lock the PRC on a sideband in a stable manner. The alignment would drift faster than we could optimize the alignment and gains for the PRC. I.e. we would lock the PRC on the carrier, align PRM (and maybe touch ITMX) to maximize POPDC, switch to sideband locking, try to lock, and things would start looking misaligned. Switching back to carrier locking, the beam spots on REFL (for example) would have moved.

Manasa noted the MC_TRANS_Y has been substantially drifting along with small drift in MC_TRANS_P as well. So we need to fix the source of the mode cleaner beam drifting if we want to make this measurement. 

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