aLIGO LHO Logbook

H1 ISC

camilla.compton@LIGO.ORG - posted 12:38, Monday 22 June 2026 - last comment - 14:15, Monday 22 June 2026(90691)

BS alignment, could see SQZ beam off ITMX fly-bys at AS Port

Betsy, Ibrahim, Oli, Keita, Camilla. Follow from 90665 where we left ITMY and SR2 in a strange location.

Summary: With ITMs back to top mass osems and BS at (P 1000, Y 1290), we have seen fly-by of SQZ beam of ITMX at AS port. Expect BS is moving to much to get steady beam. SR2 alignment very different than March/O4 (+500urad P, +150urad Y).

9am. We started by putting ITMs, SRM, SR2, SR3 back to March DRMI time sliders (11:02 PDT 19 March 2026), attached sliders. We did not like that ITM PIT top mass osem sensors were far from the March time (-30urad for ITMX, +220urad ITMY).

We tried adding -170 to the ITMY Pitch slider as per 90551, this still took us very far form the osem sensors.

9:33am We took ITMs, SRM, SR2, SR3 back back to the sensors (top mass osems) in March DRMI time (11:02 PDT 19 March 2026), attached sliders of this.

We then misaligned SRM but did not get our SQZ beam back on AS_A,B or AS_AIR camera off ITMY. We then went back to the time Thursday we had the beam on the camera at the current ITMY pitch pointing, moved according to osems for SR2 and oplev for SR3 (as HAM5 moved Thursday late afternoon 90671). Got the SQZ beam from ITMY back on the camera as per last Thursday, but this time we are happy with out ITM pointing.

We started the /ligo/home/sheila.dwyer/SUS/BS/BS_raster.xml but still could not see sign of SQZ beam off ITMX. BS was at (P 1000, Y 1000)

10:15am Went into HAM4 and moved BS sliders to get SQZ beams on top of each other: (P 1000, Y 1290). This is encouraging that even with a different ITMY position, the BS pointing is very similar to last week. Sliders attached.

On AS_A and AS_B we could see intermittent flashes of the SQZ beam off ITMX as it hit the sensors, we could also see it "fly-by" on the AS_AIR camera. We moved BS in a few 100's of counts and ITMX in ~100urad counts to try to improve this, it was intermittent (more flashes when there was more activity in the changer and when BS was not damped) but we did not improve it. Our best fly-bys are attached, typical good flashes also attached, amplitude of flashes as are expected. We'd later like to go back to this alignment.

We tried using SR2 to center ITMY SQZ beam on AS_AIR camera but the beam quality got worse we we reverted. Expect there’s a better SRC alignment could find, currently SR2 slider is ~ 500urad different than March!

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Comments related to this report

keita.kawabe@LIGO.ORG - 13:44, Monday 22 June 2026 (90692)

Link

Found the ITMX alignment that sends IMC flashs all the way to AS camera AND the SQZ beam all the way to ISCT1

But, as of now, IMC flashes don't come back to ISCT1 at all, and SQZ beam only comes back to AS camera via ITMY reflection. PRM is misalilgned.

The ITMX alignment is very different from where I started but this is expected as we have moved PR3 by a large amount when we tried to center the IMC flashes on ITMX.

sqz -> SR chain -> BS-> ITMX -> BS -> PR-chain -> ISCT1

	before/after
H1:SUS-ITMX_M0_OPTICALIGN_P_OFFSET	-96/-125
H1:SUS-ITMX_M0_OPTICALIGN_Y_OFFSET	104/-331

In the attached video (PXL_20260622_203143545TS~2.mp4), ITMY is misaligned and only ITMX reflection reaches two cameras. In the ISCT1 REFL camera you can see a big bright beam which is from SQZ, while in the AS camera you can see IMC flashes.

What we should do is to refine ITMX alignment such that we can see ITMX reflection of IMC flashes in ISCT1. After that, if the IMC flashes arestill visible in AS camera, scan BS alignment to find ITMY reflection of IMC flashes in ISCT1. If the flashes are not visible in AS camera, we need to do some math.

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Non-image files attached to this comment

PXL_20260622_203143545TS~2.mp4

camilla.compton@LIGO.ORG - 14:15, Monday 22 June 2026 (90694)

Link

Ryan S and I went back to the ITMX and BS alignment of the best ITMX SQZ beam "fly-bys", we did not see them or any flashes again.