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Entry  Tue Sep 13 14:12:03 2022, Yehonathan, Update, BHD, Trying LO phase locking again Screenshot_2022-09-13_17-41-33.png
    Reply  Thu Sep 15 21:12:53 2022, Paco, Update, BHD, LO phase "dc" control lophase_oltf.pdflophase_noise_spectra.pdf
       Reply  Tue Sep 27 10:50:11 2022, Paco, Update, BHD, calibrated LO phase noise lo_phase_asd.pdf
          Reply  Wed Sep 28 16:37:26 2022, Paco, Update, BHD, calibrated LO phase noise; update lo_phase_asd.pdf
             Reply  Wed Sep 28 21:54:08 2022, Paco, Update, BHD, calibrated LO phase noise; update dcpd_phase_asd.pdflo_phase_asd.pdf
                Reply  Fri Sep 30 20:18:55 2022, Paco, Update, BHD, LO phase noise with different actuation points BHDC_asd_actuation_point.png
                   Reply  Mon Oct 3 15:19:05 2022, Paco, Update, BHD, LO phase noise and control after violin mode filters filters_c1sus_lo1_lsc.pngBHDC_asd_act.pngboosted_lo_phase_control.png
Message ID: 17160     Entry time: Tue Sep 27 10:50:11 2022     In reply to: 17142     Reply to this: 17161
Author: Paco 
Type: Update 
Category: BHD 
Subject: calibrated LO phase noise 

Locked LO phase to ITMX single bounce beam at the AS port, using the DCPD (A-B) error point and actuating on LO1 POS. For this the gain was tuned from 0.6 to 4.0. A rough Michelson fringe calibration gives a counts to meters conversion of ~0.212 nm/count, and the OLTF looks qualitatively like the one in a previous measurement (~ 20 dB at 1 Hz, UGF = 30 Hz). The displacement was then converted to phase using lambda=1e-6; I'm not sure what the requirement is on the LO phase (G1802014 says 1e-4 rad/rtHz at 1 Hz, but our requirement doc says 1 to 20 nrad/rtHz (rms?)... anyways wit this rough calibration we are still off in either case.

The balancing gain is obvious at DC in the individual DCPD spectra, and the common mode rejection in the (A-B) signal is also appreciable. I'll keep working on refining this, and implementing a different control scheme.

Attachment 1: lo_phase_asd.pdf  185 kB  Uploaded Tue Sep 27 19:48:45 2022  | Hide | Hide all
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