camilla.compton@LIGO.ORG - posted 16:53, Tuesday 16 June 2026 (90629)
HAM7 Vent - Tuesday June 16th - realigned to FC and swapped FC WFS A, co-alignment found bad
Ryan S, Madi, Camilla
Realign to FC
Yesterday we unlocked the OPO SUS 90623 but released this slightly shifted the alignment coming off the OPO SUS towards the FC. Today, we moved A:M3 to center on the ZM3 iris and ZM3 for the retro-reflection. Sliders attached. ZM3 went from P -150, Y -660 to P -130, Y -620. We mainly moved in YAW (A:M3 only in YAW) and double checked that the height at ZM3 and FC1 was around 6.25" still. After this, beam was centered on ZM4 iris, we did not touch B:M4.
Once we did this, the beam was getting to the SQZT7 PD with minimal clipping dips, there were still some dips from max level but we compared this to nighttime June 2nd (with chamber open and OPO SUS unlocked) and it is the same.
Power through OPO SUS Check
Similar to in 90573, where we measured between 2% and 5.5% power drop. Today, total of around 1.38 to 1.44mW out of OPO, before A:DC1. Measured drop of between 0.02 and 0.08mW though to off OPO after B:M4. This is between 2% and 5.8% power drop. We expect at least 3% (1% for each SFI and 1% at B:BS1) and our power budget has 4.7% measured.
Green Misalignment
Before we started we noticed that the green beam towards FC is grossly misaligned in Pitch, attached photos at ZM1 iris (green beam low) and ZM3 iris (green beam high). We are not sure when this happened, as the SK path was very off yesterday, it could have happened before the OPO was unlocked. We will check everything is secure and then attempt to use a single pico-motor to fix this as the is the most likely thing to have got bumped.
Swapping FC WFS A
When we started the beam was misaligned in pitch on the FC WFS, very low on the lens. We moved the picos in Pitch to get the beam on both A and B. The picos both still have plenty of range. We then verified which QPD was A, marked its location with a dog, and at the chassis turned off the +/- 18V for WFS before unplugging both WFS cables. We then unplugged the WFS A and removed it, removed the diode detector holder D2000384 from the enclosure D2000246 (marked part #4) and swapped it to the new diode housing (add ICS link) and reinstalled.
Ryan caught we needed to put H1:SQZ-RLF_QPD_A_SEG_C_OFFSET back to nominal (I'd changed it in March), then everything then seemed as expected. We need to better center onto these QPDs tomorrow.
Images attached to this report
