Vicky, Camilla. Retaking OPO PZT modemattching scan from 66527 and 62691.
Set up: SQZ_MANAGER DOWN then NO_SQUEEZING, SQZ_FC to FC_MISALIGNED , SQZ_OPO_LR to DOWN, "! Toggle Seed/CLF" to let seed though, block CLF and block green pump. We turned up SEED power to 5mW, the polarization isn't good with 0.4mW rejected in HAM7 (but would need to go on table to adjust this).
Scanned OPO PZT1 with Sawtooth 400s period, plot attached for SEED.
Then reverted back to CLF, blocked CLF and looked at scan in green, decreased pump power from 22mW to 2.2mW using waveplate and H1:SQZ-OPO_ISS_DRIVEPOINT. Scan in plot attached.
Summary: OPO IR and Green cavity scans look bad due to misalignment. Mode-matching into OPO cavity looks good. From today, estimating IR_TEM00 ~ 71% (pitch misaligned), GR_TEM00 ~ 56% (yaw misaligned).
- We noticed that OPO cavity scans looked bad when we translated the squeezer crystal across the cavity (many peaks, see Oct 17, 2023 73524)
- It worse now than we measured in Dec 2022 66527 ( IR <= 82%, GR < 73% )
- But it was great when we replaced the OPO IR fiber collimator in the September 2022 vent, 64949 - with the new CLF collimator, we measured >94% IR_TEM00 mode-matching before closing HAM7.
- Note: OPO IR and GR mode-matching both look pretty good. The difference in TEM00 efficiency is misalignment. For IR, today we measured IR_TEM20_JAN2024 = 6.4%, which is consistent with Sept 2022 in-chamber IR_TEM20_SEPT2022 = 0.304/(5.48+.304) = 5.3% mismatch (from scope image). That 5% mismatch we measured in-chamber was further consistent with optics lab beam profiles of the new collimator, 63400 "This gives us 95% overlap with the target beam". For opo green, I couldn't see the TEM20 mode on the camera to clearly identify which peak it was, suggests the GR_TEM20 mode mismatch is quite small (thanks team cds for getting the sqzt7 green trans camera online 75286).
See below for details of OPO cavity scans using PZT1, while PZT2 = 0V (clf cmb slow output). We did not try the mode-matching dependence with OPO PZT 2, though that is a thing (62856, this image).
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OPO IR, 4.9 mW into seed fiber: 200 second scan, starting around 1388880769
IR_TRANS (OPO_IR_TRANS_PD has dark offset -20e-6, ignoring this)
- TRANS_TEM00 = 0.055
- TRANS_TEM01 = 0.01 (pitch misaligned)
- TRANS_TEM02 = 0.005
- Camilla calculated the sum of visible peak heights, peaks_sum = 0.0776 (=0.055+0.01+0.005+0.0019+0.0013+0.0004+0.004)
0.055/(0.055+0.01+0.005+0.0019+0.0013+0.0004+0.004) = 71% matched into TEM00
0.01/(0.055+0.01+0.005+0.0019+0.0013+0.0004+0.004) = 12.8% mis-aligned into TEM01 pitch
0.005/(0.055+0.01+0.005+0.0019+0.0013+0.0004+0.004) = 6.4% mis-matched into TEM02 *** same as Sept 2022 in-chamber mismatch (>94% IR_TEM00 coupling)
IR_REFL (refl dark offset = 30e-6, ignoring this)
- REFL_OFF_RES = 1.195
- REFL_ON_RES_TEM00 = 1.152
- REFL_ON_TEM10 = 1.187
- REFL_ON_TEM20 = 1.191
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OPO GREEN, 2.9 mW into pump fiber: 200 second scan, starting around 1388886980.
GR_TRANS (trans dark offset = 1 is already subtracted off the following)
- TRANS_TEM00 = 10.66 uW (85 V PZT1, note PDH 80 MHz sidebands)
- TRANS_TEM01 = 7.4 uW (90V PZT1, yaw misaligned)
- TRANS_TEM02 = ??? (maybe 1.02?) uW (couldn't find TEM20 on camera while scanning)
tem00/peaks_sum = 10.66/(10.66+7.4+1.02) = 56% matched into tem00
tem10/peaks_sum = 7.4/(10.66+7.4+1.02) = 39% misaligned into tem10
GR_REFL (refl dark offset = +0.004, not subtracted yet) (calibrated below into "mW")
- REFL_OFF_RES = 0.35
- REFL_ON_RES_TEM00 = 0.27 around 90V, 0.29 over 100V different at diff FSR's
- REFL_ON_TEM10 = 0.30 around 90V, 0.31 over 100V different at diff FSR's
- REFL_ON_TEM20 = ???
Unsure if any of this relates to the recent 5-6 Mpc DARM improvement after the OPO relocked from ~40V to ~95V, LHO:75281, but connecting alogs for reference.