ISC Meeting on 2020/03/09 14:00 - 15:00

Participants:

Zoom meeting: https://zoom.us/j/6676627462

Next meeting

TBD

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Minutes

Agenda

• We want to know what to do for O4 with birefringence and ITM transmission asymmetry
• Summary of measurements so far

  • X-arm round-trip loss from reflectivity is 86(3) ppm (if we assume no birefringence) https://klog.icrr.u-tokyo.ac.jp/osl/?r=7307

  • ITMX and ITMY single bounce has 12% and 15% loss, respectively, including ITM transmission and losses to p-pol. Losses to p-pol measured at POP was 9.4% for ITMX and 4.6% for ITMY. Considering BS reflectivity is different for s-pol and p-pol., this corresponds to 6.1% for ITMX single bounce and 11% for ITMY single bounce. https://klog.icrr.u-tokyo.ac.jp/osl/?r=9314 https://gwdoc.icrr.u-tokyo.ac.jp/cgi-bin/private/DocDB/ShowDocument?docid=10369

  • Carrier power recycling gain for PRMI was about 3, which corresponds to PRC intra-cavity loss of 25% or so. Considering ITMX and ITMY single bounce losses, this means that Michelson contrast defect is 10% or so. http://klog.icrr.u-tokyo.ac.jp/osl/?r=9300

  • The mount of p-pol from ITMX is smaller by a factor of 3 with X-arm locked (mode healing effect). http://klog.icrr.u-tokyo.ac.jp/osl/?r=9393

  • Carrier power recycling gain when PRFPMI is locked is 12 for X-arm and 10 for Y-arm. http://klog.icrr.u-tokyo.ac.jp/osl/?r=12639

  • X-arm round-trip loss, finesse, and mode healing effect altogether gives X-arm loss on reflection give 86 ppm * ~1000 + 6.1 % / 3 = 11 % loss. So may be PRG of 10-12 for the carrier is reasonable. This is also consistent with X-arm reflectivity measurement done before we are aware of birefringence issue. https://klog.icrr.u-tokyo.ac.jp/osl/?r=7307

  • Power recycling gain for the sidebands are 2 or so (very rough estimate).
  • DRMI on 1f is fine. Lasts 30 min or so.

  • DRMI on 3f lasts 5 min or so. https://klog.icrr.u-tokyo.ac.jp/osl/?r=12535

  • CMRR for intensity noise. https://klog.icrr.u-tokyo.ac.jp/osl/?r=13028

• Summary of calculations

  • Effect of ITM asymmtery to sensitivity: https://gwdoc.icrr.u-tokyo.ac.jp/cgi-bin/private/DocDB/ShowDocument?docid=10352

  • Effect of ITM asymmetry to ASC: https://gwdoc.icrr.u-tokyo.ac.jp/cgi-bin/private/DocDB/ShowDocument?docid=10359

  • Effect of inhomogeneity (without birefringence): https://journals.aps.org/prd/abstract/10.1103/PhysRevD.100.082005

• List of measurements to be done before the vent for O4
  • Try DRFPMI locking for one more week.
  • X-arm and Y-arm reflectivity/loss measurements with polarization considered

  • Re-measurement of CMRR for frequency noise https://klog.icrr.u-tokyo.ac.jp/osl/?r=13069

  • Measure power recycling gain for sidebands (POP 2f with FPMI locked and PRFPMI locked)
  • Measure MICH contrast defect with MICH locked and FPMI locked
  • OMC cavity scan to scan mode content of AS beam
  • Scattered light measurement in PRC by sweeping PRM and PR2/3 deferentially.
• List of calculations to be done
  • DRFPMI LSC and ASC sensing matrix with birefringence and ITM transmission asymmetry
  • Frequency noise and intensity noise coupling with birefringence and ITM transmission asymmetry
  • MICH/PRCL/SRCL to DARM coupling with birefringence and ITM transmission asymmetry

• O4 Schedule https://gwdoc.icrr.u-tokyo.ac.jp/cgi-bin/private/DocDB/ShowDocument?docid=9209

• Executive summary (tentative)
  • We are not sure yet whether birefringence is limiting our sensitivity and stability. DRFPMI locking probably possible with current interferometer.
  • Putting polarizers inside PRC and SRC might improve the sensitivity and stability, but it might introduce some extra issue (thermal lens, extra loss, scattered light etc).
  • May be better to focus on characterization of the interferometer and the preparation of better ITMs rather than the preparation of polarizers.
  • It is always good to prepare for the unexpected if we have manpower and money. Preparing polarizers now might save our lives in the future.
  • Measurement listed above must be performed before the vent for O4 to characterize the current situation and to make a plan for O4.