Jennie W, Sheila,
We turned off the 9 and 45 MHZ sideband EOMs and unplugged the 118 MHz modulation at the PSL racks. See this alog for how to do this.
We locked the IMC and mis-aligned ITMX.
DC centering loops 3 and 4 were turned on.
Sheila took the OMC lock guardian to PREP OMC scan and turned on the OMC ASC.
We waited for this to converge then turned it off.
We turned input power up to 10W from 2W and then locked the OMC in length manually by using the PZT offset slider to search for a high peak ~ 15mA.
After finding it we turned on the locking with a gain of 24 and the boost and int filters on (we checked the settings we needed in the guardian as we couldn't get the OMC guardian to lock it for us).
Then we turned off the OMC ASC.
We tuned up the OM3 and OMC alignment slightly to maximise the power on OMC-DCPD_SUM_OUTPUT and minimise it on OMC-REFL_A_LF_OUT16.
OM3 was moved down in yaw only from -108 to -117 and OMC was moved down in yaw from 210.5 to 195.5 and down in pitch from 350.4 to 340.4. The final values for the sliders are here.
Quiet time locked after aligning 16:21:03 UTC - 16:24:13 UTC
OMC-REFL_A_LF_OUT16 = 0.652644 mW
OMC-DCPD_SUM_OUTPUT = 15.6162 mA
Quiet time unlocked 16:25:31 UTC -16:27:35 UTC
OMC-REFL_A_LF_OUT16 = 30.106 mW
OMC-DCPD_SUM_OUTPUT = 0.000456763 mA
We took the IMC guardian offline and shuttered the green light going into both arms at the ISC tables, and with ISC_LOCK guardian in idle so it wouldn't keep trying to relock IMC.
Quiet time dark measurement 16:43:38 - 14:46:19 UTC
OMC-REFL_A_LF_OUT16 = -0.0132979 mW
OMC-DCPD_SUM_OUTPUT = -0.00106226 mA
The scan template is saved as /ligo/home/jennifer.wright/Documents/OMC_scan/2024_04_16_OMC_scan.xml
With the references for the time series of the three pertinent channels as:
Ref 0 OMC-DCPD_SUM_OUT_DQ
Ref 1 OMC-PZT2_EXC
Ref 2 OMC-PZT2_MON_DC_OUT_DQ
I ran Sheila's code from this entry, altered with the measured input/output coupler transmission of the current OMC which can be found on Page 116 on LIGO-T1500060.
The output gives this for the cavity parameters:
Power on refl diode when cavity is off resonance: 30.138 mW
Incident power on OMC breadboard (before QPD pickoff): 30.589 mW
Power on refl diode on resonance: 3.879 mW
Measured effiency (DCPD current/responsivity if QE=1)/ incident power on OMC breadboard: 59.5 %
assumed QE: 100 %
power in transmission (for this QE) 18.203 mW
HOM content infered: 9.763 %
Cavity transmission inferred: 66.439 %
predicted efficiency () (R_inputBS * mode_matching * cavity_transmission * QE): 59.509 %
omc efficency for 00 mode (including pick off BS, cavity transmission, and QE): 65.948 %
round trip loss: 3504 (ppm) Finesse: 335.443
I will cross-check the HOM content inferred by analyaing the C02 mode height from a cavity scan.
The mode-matching inferred from the height of the carrier 02 mode vs. the carrier 00 mode from the scan is 0.0983 mode mis-match = 9.83%.
The mode scan fit and the C02/C20 fit are attached.
The code is on labutils /dev branch
The code for the full scan can be ran using:
python OMCscan_nosidebands9.py 1397320410 80 "Cold OM2, 10W PSL, pre-output loss" "single bounce" --verbose -m -o 2
The code for the C02 fitting can be done using:
fit_two_peaks_no_sidebands9.py
Where the blue trace is the data, the orange is the fit, and the purple is the function plotted with the inital guesses for the fit parameters as a cross-check.