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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: 11815     Entry time: Wed Nov 25 23:17:34 2015     Reply to this: 11827   11870
Author: yutaro 
Type: Update 
Category: LSC 
Subject: strange behavior of ASDC 

[yutaro, Koji]

I noticed that ASDC level changes depending on the angle of ITMY when trying to take some data for loss map of YARM. We finally found that ASDC level behaves strangely when the angle of ITMY in yaw direction is varied, as you can see in Attachment 1. Now, AS port recieved only the reflection of ITMY. 

NOTE: This behavior indicates that angular motion could couple to length signal in AS port.      

Koji suggested that this behavior might be caused by interference at SR2 or SR3 between main path light and the light reflected by the AR surface. By rough estimation, we confirmed that this scenario would be possible. So it would be better to measure AR reflection of the same mirror to ones used for SR2 and SR3 in term of incident angle.     

Ed by KA: This senario could be true if the AR reflection of teh G&H mirrors have several % due to large angle of incidence. But then we still need think about the overlap between the ghost beam and the main beam. It's not so trivial.

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