camilla.compton@LIGO.ORG - posted 11:19, Thursday 24 February 2022 (61892)
HWS ITMX SLED replaced, both HWS SLED beams alignment to iris good
Yesterday I opened the HWS table (layout D1400252) next to HAM4 and plugged in the last two cables (alog61545) 18V Power and Polar_PD_ADC to the Poloizaton PD whittening box D1500430 (do we use these signals?).
I replaced the ITMX 790nm SLED as this beam had been decaying over time (alog58569) old S/N 06.18.001, new S/N 06.18.002. ICS and SLED stock alog58758 will be updated.
Before swap POWERMON read 0.08mW, now POWERMON reads 0.4mW and using Ophir Power meter (@900nm) measured 2.3mW out of the collimator. There is a discrepancy here- I think because the PDs are measuring power of the beam reflected off ITM, unsure what calibration POWERMON uses.
I adjusted the ILIM trim point in the chassis. In theory to 485mV on test point ~ 120mA current ~ 2.5mW max output. In reality the maximum current this SLED is drawing is 108mA. Power is sufficient so will leave be.
The ITMY 840nm SLED still looked good, this was replaced in March 2021 (alog58074 ). POWERMON reads 2.08mW and using Ophir Power meter (@900nm) measured 1.3mW out of the collimator.
Checked that both SLEDS were aligned to the two on table irises. No adjustment was needed. This is one of the steps of the HWS vertex aligning procedure T1700163 that we will continue to follow today.