jeffrey.kissel@LIGO.ORG - posted 21:47, Thursday 11 September 2014 - last comment - 07:18, Friday 12 September 2014(13893)
ITMY Optical Lever Molesting
J. Kissel, R. Adhikari In attempts to investigate the long-term, sawtooth drift seen in the H1 SUS ITMY's optical lever (see LHO aLOG 13863), Rana and I went out nudged and poked things on the transmitter/ laser launcher side of things. I attach a time series of the optical lever signal over 4 hours, starting at 2014-09-11 2349UTC, or roughly 4:50p local, and explain the timeline below. - At around 5:44p local (marked in mustard yellow), Rana gave the pylon a couple of hefty nudges to see if anything was loose. This clearly shifted the pylon in yaw, but had no affect on the sawtooth. - For the next 10 minutes (between yellow and black), we wandered around the LVEA locking for wrenches to tighten down the nuts and bolts connecting the pylon to the concrete. - Having found some, we then cranked on all accessible bolts (marked in black). This moved the pylon in yaw some more. - Realizing we needed to open the hood to get it realigned (we got no action out of moving the ITM around), we looked for some allen keys (between orange and black). - During this time, you could convince yourself that the sawtooth remained. - Once we got back, we opened the lid, which pushed the beam off the edge of the QPD (marked in red). - We then unlocked the pitch and yaw adjustment micrometers, and re-centered the beam on the ITM (marked in blue). - After recovering the transmitter, Rana went to Daniel's for dinner, and I came back into the control room. - At around 7:25p local, Kiwamu misaligns ITMY to work on PRX cavity locking, so the beam falls off the QPD again (marked in green). - At 8:10p local, he realigns ITMY into a Michelson configuration -- and voila! sawtooth has reduced. The message: I think this means that the problem lies in the QPD. Maybe one of the quadrants in bad, such that depending on the location of the spot on the QPD this drift is more or less prominent. I'll try walking the beam around the QPD for the next hour or so before people come back from dinner to see if I can nail down the problematic quadrant.
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J. Kissel Moved the H1SUSITMY around with alignment sliders to a few different positions while we were debugging the PSL to explore the optical lever QPD, looking for bad quadrants. Trend of exploration attached. No clues on a particular bad quadrant, sawtooth problem seems to be systematic to all quadrants. Alignment values Time P Y -80 mins 151.8 -93.1 (good for MICH alignment) -60 mins 151.8 -80.1 -20 mins 161.8 -83.1
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Jason and I discussed testing the Photo Diode with a laser pointer to see if it is the PD or perhaps the electronics once they have a voltage on them.