Naoki, Vicky, Sheila, Camilla. WP 11470.
OPO Crystal Move
Following last time we moved the OPO crystal 65684, we used the wincam dell laptop and gray E-870 PI shift driver box (stored in LVEA SQZ cabinet) and the OPO crystal cable Daniel attached the the +X HAM7 flange. Adjusted OPO temperature from 31.684 degC to 31.804 degC for co-resonance while scanning rather than stationary.
To scan the OPO PZT fast enough, we used external function generator and Thorlabs driver at the racks for the OPO PZT to scan over more than 1 FSR (around 1-9V scan).
We were able to move the OPO crytal over its full range and found 6 spots with red/green co-resonance, attached pdf shows the places we moved. LLO found 10-13 potions which is surprisingly more than us, 73502.
Through O4 we've been using the 2nd posltion from the right, but left the crystal on the 2nd spot from the Left.
Photos attached of the PZT scan (yellow trace), OPO IR trans light measured on HD PDA (pink trace), Green trans from CLF path (green trace). The green alignment looked bad at all spots. This could be from misalignment of OPO path or HOMs present in fiber. When we next go into HAM7 we can look at this.
NLG Measurement
Turn down green pump power with SQZT0 wave plate to 4mW in to stop the OPO lazing. We measured NLG of 14 (OPO_IR_PD_LF_OUTPUT amplified / unamplifed = 0.0136/0.00092). This reduced to NLG of 12 over a few minutes.
Homodyne Measurement
We balanced the HD by reducing the seed power and realigned to maximize visibility. At start of measurement visibly was 14 and at the end it NLG was 12. Vicky, Sheila Naoki took Homodyne measurements which were hard with NLG drifting. Measured 4.5dB whihc is less than the 6dB measured last week 73376. But we think we could have offloaded the ASC alignments incorrectly to not see good SQZ on the HD.
- PDA 98.6% Visibility (Min 10.3mV Max 1.48V) = 2.75% loss (1- Vis^2)
- PDB 98.0% Visibility (Min 14.8mV Max 1.5V) = 3.87% loss
SQZ in IFO
Ended with NLG of 13.5 into IFO. Amplified power of 0.0196, unamplified seed of 0.00149. Though this may be changing quickly.
Took some no sqz data while TJ tested updates to the Observing with No SQZ wiki. Accepted sdfs to go back into observing. Vicky adjusted OPO tempurature and had to adjust the SQZ angle from 142 to 163, squeezing looks better 4dB+ but we expect the angle and OPO tempurature may need to be adjusted over the next hours...
On the bad alignment of the green to the OPO shown in Camilla's photos of the scope:
We normally apply an offset to PZT1, which we were not doing this morning. This offset impacts the cavity alignment, as you can see in Vicky's screenshots from April 2022. 62856
Here are some past alogs showing an OPO cavity scan with the green transmission.
Dec 2022: 66527 (we should do a repeat of a scan like this now, with lowered green power and a slow scan, to see if things have really degraded).
April 2022: 62691
Sept 22 we swapped the CLF collimator.
With this new crystal position, we have more squeezing in DARM, at first briefly measuring ~4.8 dB SQZ at 2kHz! It has since settled to ~4.2dB in Observe. As Camilla said, this is with the 2nd spot from the left edge (5th from the right). The optimal OPO temperature will be changing as it settles into this new spot, so there we may need to tune co-resonance temperature over the next few days to re-optimize.
Just before injecting SQZ to the interferometer, with OPO trans = 80uW, NLG was measured as 13.15. We took some sqz/asqz/meansqz loss measurements, and will do subtraction using the following times. Measurements using dtt cursors:
- SQZ, ~4.8 dB
- 1381612908 - 1381612998
- No SQZ
- 1381613053 - 1381614325
- Anti-sqz, 14.0 dB
- 1381616445 - 1381616576
- Mean-sqz, 11.0 dB
- 1381616609 - 1381616740
- After 22:33:40 UTC (gpstime 1381617238), we went back to Observe with SQZ at this spot.
Loss analysis and subtraction to follow.
NLG variation over an early ~6min of operating at this new spot is interesting. I think we see the crystal's green losses increasing rapidly. In the screenshot, the OPO was locked in green (~80uW green transmitted power, but no intensity stabilization so green power varied).
- We see the crystal's non-linear gain decrease by ~11.7% over 6 minutes for fixed input green power (NLG = (max_amplified/unamplified) ; the top red trend shows decay of the maximum amplified seed power. The maximum amplified seed power can be found by optimizing the OPO crystal temperature, but this decay of NLG was not recoverable by optimizing crystal temperature (bottom trend = attempts to optimize opo crystal temp).
- NLG decay does look consistent with the decay of transmitted green power over ~6 minutes. The decay of green transmission for fixed input green power could result from fast crystal losses/absorption/etc in green. This lowered green pump power, results in a lower non-linear gain for red/sqz. That is, I think this NLG decay can be explained by fast green losses in the opo crystal, and doesn't necessarily require fast variations in red (i.e. these fast green losses don't have to also be fast red sqz losses).
edited to include: NLG measured ~7 hours later in the lockloss. After ~4 hours with stabilized green trans = 80uW, the opo co-resonance changed from 31.638 degC to 31.617 degC, and we recovered the same NLG after tuning the temperature, so the interaction strength (probably also the red losses) did not degrade much in this time.
edited to include darm sqz 15 min after relocking: SQZ reached 4.8dB again after relocking; the darker bottom SQZ trace is taken ~15 minutes into this next lock. This is operating at the new spot for ~8 hours.
For these squeezed darms at the new crystal spot, here's adding in subtracted sqz data for these times of anti-squeezing, squeezing, and mean-squeezing (i.e. LO loop unlocked, sqz phase is unlocked from the IFO beam and spinning through all sqz angles).
