aLIGO LHO Logbook

H1 SQZ

camilla.compton@LIGO.ORG - posted 17:15, Monday 17 October 2022 - last comment - 13:04, Tuesday 18 October 2022(65370)

Checking SQZT7 FCGS and OPO Trans alignment

Naoki, Wen, Camilla

Today Jim turned on the HAM7 ISI and we checked the alignment of the FCGS and IR OPO Trans alignment to the irises Sheila and I set in alog 65164, I was surprised that neither beams were well aligned with the Zms in the iris settings (30 Sept) alignment.

The FCGS beam on was too high and clipping on the lower periscope mirror, images on LPM and 1st iris attached. The IR OPO Trans beam couldn't be seen.

When we changed ZM3 (not a long term solution, was changed back) to the alignment Naoki found in alog 65334, we could see the OPO trans beam (it was a little low on the camera) and the green FCGS beam became very well aligned.

Jim helped show me that this amount of mis-alignment can't be accounted for from the HAM7 ISI, locationmon's (units nm and nrad) attached. Largest changes bettween Sept 30th and today are 38um in Z and 20urad in RZ, both very very small. I estimate we are seeing a change of the FCGS of 5mm over 3m which is 1.5mrad.

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Comments related to this report

wenxuan.jia@LIGO.ORG - 20:40, Monday 17 October 2022 (65371)

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The flipper cable can easily block the FCGS beam before fiber. I'll make sure to fix it when LVEA is globally laser hazard.

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camilla.compton@LIGO.ORG - 13:04, Tuesday 18 October 2022 (65379)

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OPO doesn't appear to have changed much though it isn't clear to me what unitits these OPO_M1_DAMP_{}_INMON s are in.

ZM1, ZM2, ZM3 L changed by ~50um each. P of ZM1 changed 150urad, Y changed 100-200urad each.

ZM4, ZM5 L changed by ~50um each. P of ZM5 changed by 400urad. Y changed 100-200urad. Reminder that FCGS doesn't depend on ZM4/5 pointing but OPO IR SQZ beam does - layout cartoon.

We are most concerned with a L or P movement as our FCGS beam seems to have risen ~5mm.

150urad of P change in ZM1 double passed (as beam reflects of ZM1 twice) over ~15m could account for 4mm of change..?!

If this is correct I think that the irises we set up can't tell us much about the co-alignment as the SUS change too much while pumping.

Sheila suggests going forward we could set up new iris after realigning the SQZT7 paths to monitor co-alignment going forward or Sheila suggested the last resort of a new HAM7 beam diverter for the not installed E-path (SQZ inspection/insertion) if we continue to be concerned the co-alignment.

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