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Mon Jan 20 20:20:36 2020, gautam, Update, PSL, PMC servo checkout 
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Wed Jan 22 11:22:39 2020, gautam, Update, PSL, PMC modulation depth measurement
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Wed Jan 22 20:12:36 2020, gautam, Update, PSL, PMC demodulator electrical characterization 
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Thu Jan 23 14:37:05 2020, gautam, Update, PSL, PMC VGA chip damaged?
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Thu Jan 23 16:37:14 2020, rana, Update, PSL, PMC VGA chip damaged?
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Thu Jan 23 22:10:01 2020, gautam, Update, PSL, PMC servo pulled out
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Fri Jan 24 15:42:08 2020, gautam, Update, PSL, PMC servo restored
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Sun Jan 26 13:47:00 2020, gautam, Update, PSL, PMC servo characterization   
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Tue Jan 28 14:33:24 2020, gautam, Update, PSL, Inferred free-running frequency noise 
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Thu Jan 23 18:52:31 2020, gautam, Update, PSL, PMC RFPD characterization
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Message ID: 15139
Entry time: Wed Jan 22 11:22:39 2020
In reply to: 15135
Reply to this: 15143
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Author: |
gautam |
Type: |
Update |
Category: |
PSL |
Subject: |
PMC modulation depth measurement |
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Summary:
I estimate the PMC servo modulation depth to be approximately 50 mrad. This is only 15% lower than what was measured in Jan 2018, and cannot explain the ~x50 reduction of optical gain measured earlier in this thread. Later in the day, I also confirmed that the LO input to the ZAD-6 mixer is +7 dBm. So the crystal is not to blame.
Details:
- PSL frequency is locked to the IMC length.
- Arm lengths are locked to the PSL frequency using POX/POY.
- EX green laser locked to the X arm length using end PDH servo. GTRX was ~0.4 in this measurement, which is the nominal value.
- The 20dB coupled port of the beat between the EX and PSL lasers was monitored using the AG4395A in "Spectrum" units.
- The beat was set at ~90 MHz, and a spectrum was taken for ~100 MHz span centered at the beat frequency.
- The modulation depth is estimated by considering the ratio of power at the beat frequency relative to that 35.5 MHz away. See Attachment #1.
Assuming a finesse of 700 for the PMC, we expect an optical gain of 2*Pin*J0(50e-3)*J1(50e-3)/fp ~ 1.2e-7 W/Hz (=0.089 GW/m). I can't find a measurement of the PMC RFPD transimpedance to map this onto a V/Hz value. |
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