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Message ID: 5393     Entry time: Tue Sep 13 09:16:00 2011
Author: Suresh 
Type: Update 
Category: IOO 
Subject: MC spots recentered and input beam aligned 

The shift of MC2 which Rana noted caused the beam spots on the MC mirrors to decenter. I used the mcassUp and mcassOn scripts and checked the output of the C1IOO lockins to get the spot positions.  I first tried to realign just the MC2 to recenter the spots.  But this was not sufficient.  I then worked on the pitch of all three optics since it is easier to align.   By the time this was done the offset in yaw also reduced, probably due to cross coupling between pitch and yaw in the coils.  At the end of the process I obtained all decentering around 1.5mm or less, then I went over to adjust the MC2TransQPD beam path so that we center the spot on the QPD.  This action shifted the stack,  I had to iterate this two more times before the successive corrections grew sufficiently small.  I think it may shift again if we touch the chamber (the image of MC2Face is still inverted).

The new spot positions in mm (MC1,2,3 pit MC1,2,3 yaw):
    1.3212   -0.8415    0.6795   -1.4292   -0.3574   -1.5208


 mcdecenter20110912_1.png    mcdecenter20110912_2.png      


- Further improvement of beam centering can be done but first I would like to be sure that the MC is stable.  The MC2Trans light is centered on the QPD as a reference.


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