Ryan S, Sheila
In summary, after removal of the A:L2 apperture stop we still see about 4% extra losses in HAM7. We searched for the rejected beam from SFI1 in both directions with lights out, IR card, and viewer. To explain a few % loss we should expect to have 10-20urad in this beam, which should be visible with lights out an a viewer. We also noticed that the beam is off in yaw at the location where we had an iris after ZM1.
Since Ryan and Camilla aligned the beam onto the SQZT7 PD yesterday, we are noting the power on that PD here after each measurement so we can use that to account for fluctuations in power out of the OPO.
- out of OPO 1.354mW std 0.5uW PD 1.26-1.154 max-min, repeat in same location 1.340mW std 0.57uW PD: 1.26-1.154 max-min
- after ZM4: 1.209mW std 11.5uW PD 1.233-1.12
- PD ratio: 98% power dropped during measurement
- power meter ratio: 89%(1st meas) or 90% (2nd meas)
- after BL1: 1.265 mW std 2uW PD 1.241-1.14
- before BM1 (SFI1 return): 1.268 mW std 582nW PD 1.23-1.11
- Remembered to start turning lights off
- before ZM1: 1.342 mW std 688nW PD 1.24-1.11
- after AP1 before SF1 (on the way to FC): 1.316 mW std 680nW PD 1.235- 1.08
- before BM1: 1.267 mW std 831nW
- on SQZT7: 1.191 mW std 5uW PD: 1.2032 much quieter with curtain up (9.5% loss where we expect 4%)
From the control room, we dithered ZM2 + ZM3 and tried to reduce the fluctuations in the SQZT7 IR PD, we were able to recover a 4% of power this way, with fairly small adjustments (+9urad ZM2 P, +19 urad ZM2 yaw, 5 urad ZM3 yaw).
One more round of power measurements:
- out of OPO: 1.334 mW std 480nW PD 1.248
- on SQZT7: 1.217 mW std 2.8uW (8.8% total loss)
- before BM1: 1.265 mW std 600nW PD 1.25 (5% losses from 2 passes of SFI1)
- after BL1: 1.272 mW std 1.6uW PD 1.25 (no loss from B:L2 apperture stop)
- after ZM1: 1.307 mw (not perfectly centered) PD 1.25 (2% loss from 1 pass of SFI1)
- on SQZt7: 1.227 mW std 900nW PD 1.25 (8% total loss)
After all of this power budgeting, OPOS rebalancing, ZM4 PSAM preloading adjustments, and alignment, this afternoon I took another (possibly the last?) ZM4/5 PSAM M^2 grid on SQZT7. Data files attached. I used different strain gauge values for ZM4 than in the past since they've shifted with the preloading change, but this still covers pretty much the whole PZT range.
This was a 26-point grid using the following PSAM strain gauge settings:
ZM4 PSAMS = [-2.6, -1.0, 1.0, 4.0]
ZM5 PSAMS = [-8.0, -6.75, -5.5, -4.5, -3.3, -1.0]
The attached plot shows the qs measured on SQZT7 propagated to SRM, with three different ZM4 preloads. Camilla has summarized the history of our ZM4 + ZM5 preloading in 91404
The blue points here are with 75 in lbs on ZM4, as adjusted in 75677. The teal points were after an attempt to lower the pre-load to 65 in lbs, which Rahul and Camilla later rechecked with the torque wrench and thought that it went to something between 40-60 in lbs. ( 91416)
On Wensday, Rahul and Camilla believed that they applied more torque to the psams (91416), but somehow the beam profiles that Ryan took show that the preload was reduced instead.
We did not repeat the OMC scans at this preload. The M^2 range is similar to previous measurements, but the astigmatism is a little better here.
