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Message ID: 10493     Entry time: Thu Sep 11 00:27:39 2014
Author: Jenne 
Type: Update 
Category: SUS 
Subject: SRM oplev touch-up 

The sum vs. pitch and yaw signals for the SRM QPD weren't making sense to me - centering on the PD lowered the sum, etc.  So, I had a look at the SRM oplev setup. 

The beam going in to the chamber looked fine, but the beam coming out was weird, like it was being clipped, or diffracted off of a sharp edge.  The beam was spread out in yaw over almost 1cm as seen by eye.  I looked into the vacuum window, and the beam was sitting on the edge of one of the in-vac steering optics.  So, I adjusted the yaw of the beam-launching optic on the out of vac table so that I was roughly centered on both of the in-vac SRM steering mirrors.  This required moving the first out of vac mirror for the SRM oplev path on the way to the QPD to move a small amount to one side, since the beam was near-ish the edge of the optic.  I then centered the beam on the oplev (I had the SRM roughly aligned already). 

Now the SRM oplev makes more sense to me.  I have turned on FMs 1, 2, 5, 9 to match ITMY's loop shape.  I have set the gains to -10 for pitch and +10 for yaw, to make the upper UGF about 6 Hz.

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