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Entry  Wed Nov 25 23:17:34 2015, yutaro, Update, LSC, strange behavior of ASDC 14.png
    Reply  Mon Nov 30 16:33:06 2015, ericq, Update, LSC, strange behavior of ASDC AScentering.png
       Reply  Mon Nov 30 18:27:30 2015, Koji, Update, LSC, strange behavior of ASDC 
    Reply  Thu Dec 10 12:33:04 2015, yutaro, Update, LSC, strange behavior of ASDC 07.png28.pngASDC.png
       Reply  Thu Dec 10 19:53:22 2015, yutaro, Update, LSC, strange behavior of ASDC 30.png11.png49.png
Message ID: 11827     Entry time: Mon Nov 30 16:33:06 2015     In reply to: 11815     Reply to this: 11829
Author: ericq 
Type: Update 
Category: LSC 
Subject: strange behavior of ASDC 

One possible explanation of this behavior is simply poor centering of the AS beam on AS55 (whose DC level provides ASDC, if memory serves me correctly).

I misaligned ETMY, and moved ITMY through its current nominal alignment while looking at the POYDC and ASDC levels. 

In both pitch and yaw, the nominal alignment is fairly close to the "plateau" in which the AS beam is fully within the PD active surface. I.e. it doesn't take much angular motion to start to lose part of the beam, and thus introduce a first order coupling of angle to power. (Look at the plateaus at around -2min and -0.5min, and where the rapidly changing oplev trace crosses zero)

Furthermore, POYDC seems to be in some weird condition where it is actually possible to increase the reported powerwhen misaligning in pitch, but somehow there is more angular coupling in this state. 

In any case, I would advise that the POY11 and AS55 RFPDs have their spots recentered with optics in their nominal aligned states. In fact, given how we found REFL11 alingment to be less-than-ideal not so long ago, all of the RFPDs could probably use a checkup. 

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