aLIGO LHO Logbook

H1 ISC

camilla.compton@LIGO.ORG - posted 17:00, Tuesday 06 May 2025 (84292)

ISC Alignment Work, Day 5 in HAM1: DC centering loops working, REFL alignment finished (apart from BDs), 2W now into IMC

Oli, Keita, Elenna, Jennie, Sheila, Ryan S, Ryan, Jeff, Camilla

Day 1: 84193, Day 2: 84228, Day 3: 84230 and 84239, Day 4: 84274

Realsied that yesterday we had the POP aligned causing flashes and need to have ITMX misaligned to work on the REFL path best. Elenna and Keita re-took the final two REFL path beam profile measurements, Travis and I turned down the purge air for these. Turned back up to maxium afterwards.

Rahul installed PM1, slightly out of the way of the POP path so it will need to be moved ~12" to be in it's final postion. It's beam dump will later be added.

Oli, Shiela and I recentered the ASC REFL B diode as yesterday we left it with the beam off mostly off the diode. We swapped the pico cables to the two on sled picos so now the match the medm labels and tested them both. Sheila then centered ASC REFL B using picos. Around 400 NSUM counts on each diode with 200mW of PSL beam in.

Elenna, Sheila and Jeff did some troubleshooting of the DC centering loops (use ASC REFL A and B signals and feedback to RM1 and RM2), there was two issues: one was that the RM1 and RM2 sign flip was no effecting the LOCK filters, Jeff chnegd this (see 84289), secondly it seemed that what was the DC signal of ASC REFL A is now ASC REFL B, Ryan is doing some alog digging to check if this was known in the last HAM1 vent. It's possible the DC signals have just been the wrong way around and this would make some sense why the pico labeled were swapped, but if the RF signals are swapped it will cause lots of issues locking the IFO. After these things were fixed, the DC centering loops were working.

Oli and I found the position the LSC sensors should be to have the beam radius on the diodes to be ~0.25mm and placed them there, aiming from 0.2 - 0.3mm. Beam profile attached at 165mm from M6 BS HR surface to front of BS, adding 5mm for diode body placement to account for the distance in front of body the diode is and that the measurement plane of scan is 0.74mm behind the surface.

We placed both LSC REFL A and B 170mm from the HR surface of the M6 BS. We aligned these by eye and got 0.4 on each H1:LSC-REFL_{A,B}_LF_OUT16, we dumped the reflected beams. Once the DC centering loops were on, Elenna and myself then checked that the beams were centered by using the steering mirrors and ndscope channels. Also checked the pico motor in the REFL path worked in PIT and YAW.

Oli turned up the PSL input to 2W and then de-energized and locked out.

Elenna and I could then see POP flashes, we started to align the periscope but ran out of time before finishing.

ITMX left misaligned so there3's no POP beam.

Images attached to this report