Attached are the averaged squeezing and anti-squeezing DARM spectra for each PSAM value we've measured so far.  Based on the course scan, we see that our initial PSAM values (strain voltages of 7.22/-0.71 for ZM4/ZM5) appear to be roughly optimal, giving roughly -5.2 dB of squeezing and 15.6 dB antisqueezing at 2 kHz.  So far we've noticed that any significant movement of the PSAM setting for ZM5 seems to de-optimize things and we are relatively insensitive to changes in ZM4 when ZM5 is held fixed at its initial value.    

Values from yesterday afternoon are also included.

On April 9th, we took one more PSAMS data. This PSAMS setting might be better than the nominal 170/95 (strain voltage 8.8/-0.66) as reported in 77074. We may come back to this setting later.

asqz 125/136 (strain voltage 7.5/0.5) (5 min)

PDT: 2024-04-09 15:36:49 PDT
UTC: 2024-04-09 22:36:49 UTC
GPS: 1396737427

sqz 125/136 (5 min)

PDT: 2024-04-09 15:43:59 PDT
UTC: 2024-04-09 22:43:59 UTC
GPS: 1396737857

Subtracted SQZ dB's for the various PSAMS settings last week: course trial #1: 76925, and course trial #2: 76949, and the previous optimzations in LHO:76507, which used SQZ ASC to hold alignments when moving PSAMS before ZM alignment scripts 76757.

I sorted the PSAMS tests by positive and negative ZM5 strain gauge voltages.

Some takeaways: hard to interpret what's happening. Could be interesting to try ZM5 strains around 0 - 0.5 V, and scan with e.g. ~0.1 V steps. I wonder if reviving the psams scanning scripts, and doing fine optimizations, would be productive at this point. I'm not sure if there's a tension between good squeezing at 1 kHz vs. 100 Hz. But some settings that give the most kHz squeezing (negative ZM5 strain) don't necessarily show the best 100 Hz squeezing (positive ZM5 strain), and vice-versa. It may just be that the optimal point is narrow, and we're taking big steps?

• For best SQZ at 1 kHz - we seem to more reliably see this with ZM5 strains between (-0.7 , 0.5) V across a large range of ZM4 settings, even when settings are varied on the same day/lock.
• For best SQZ at 200 Hz - a bit hard to say, but possibly ZM5 > 0 (positive) gives better 200 Hz SQZ.  
  • Several negative ZM5 traces suggest freq-dep losses below the DARM pole.
  • For positive ZM5 traces, very hard to tell. SQZ looks lossier for ZM5 > 2V.  

Attachment 1 - positive ZM5 strain - potentially more SQZ at 100 Hz, and less sqz at 1 kHz?

• Some of these traces have flatter SQZ, but this is hard to disentangle from just loss, since many positive ZM5 settings have both less SQZ and less ASQZ.
  • Like as an example, if SQZ-OMC mode-matching was very bad for those settings, squeezing would just look lossier across the whole band, which might cause it look flatter too.
  • But I think the blue (7.2, 0.3) trace is an interesting counter-example: we could infer that there's less generated squeezing (b/c anti-sqz is lower), but the decrease in anti-sqz is not due to loss b/c squeezing is the same.
  • Comparing the blue 4/4 to the pink 3/17 is also interesting - PSAMS settings are very similar, and shape of SQZ is very similar (blue / pink nearly parallel). But, anti-sqz (= NLG + loss) is less on 4/4 than on 3/17, while sqz (~ loss) is basically the same. This could suggest less generated squeezing on 4/4 than 3/17.
• Higher ZM5 settings far above 1V are not obviously good. In this range, both asqz+sqz look worse.

Attachment 2 - negative ZM5 strain - more kHz SQZ, but kinda looks lossier below the DARM pole at e.g. 100 Hz.

• Mostly, ZM5 strain is at -0.7V, and ZM4 is varying. 
• This looks consistent with the FD-SQZ data set on 20 March LHO:76540, which used PSAMS at ZM4/ZM5 = 150 / 90 (8.46V, -1.26 V).
  • Fitting a common sqz model to that 3/20 data suggested there were freq-dep losses below the DARM pole at those settings (plot). There's also evidence for the freq-dep losses at 100 Hz in this 4/4 data.

Linking LHO:75749 with the in-chamber beam profiles at various PSAMS settings, as we continue working to reconcile the models and measurements.