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Entry  Tue Sep 18 18:24:50 2012, Jenne, Update, General, Scattering in BS chamber or ITMX chamber 
    Reply  Wed Sep 19 01:08:48 2012, Jenne, Update, General, DRMI aligned again DRMI_aligned_19Sept2012_ETMYwasHighNeedToFix.png
Message ID: 7402     Entry time: Tue Sep 18 18:24:50 2012     Reply to this: 7405
Author: Jenne 
Type: Update 
Category: General 
Subject: Scattering in BS chamber or ITMX chamber 

I have touched PZT2 such that the beam goes through the 45 degree non-iris target on the beam splitter.  This puts the beam at the center of ITMY, and without moving the BS, at the center of ITMX.  I say "at the center", but what I really mean is I put the target approximately at the center, within what looks like, say, 2 mm, by looking from above.  The target was many (5ish) centimeters away from the optic though, so that's why my side-to-side centering isn't so precise.  Given that, the beam was always more than half going through the hole of the target for both ITMs, so I'm claiming that the spots on the ITMs are within a few mm of center.

With this alignment, the beam was also hitting the center of the SRM (with all the same caveats).

I was able to get the SRM to retroreflect, while I still had Michelson fringing, so I think that I had the SRMI at least close to aligned (I was looking at the SRM retroreflection at the beam splitter, not all the way out to the AS port).  PRM is also pretty easy to align.

We're hitting the top of the AS camera, so I think things are pretty good.  I don't see beam on the REFL camera, but no investigation of that has been done as yet.

There is some scattering going on in the BS / ITMX chambers that's making me kind of unhappy.  I don't know how to get this to embed the youtube video, so here's the embed link, as well as the regular link:

youtube of AS and BS/PRM camera.

<iframe width="420" height="315" src="http://www.youtube.com/embed/QUbnMLXSS5U" frameborder="0" allowfullscreen></iframe>

Manasa watched the camera while I waved an IR card around in the BS chamber, and the only way I was able to get all the scatter spots to go away was to either block the beam incident on the BS (duh), or block the beam reflected off the BS, heading to ITMX.  Manasa said that the scatter spots still looked like they were fringing though, so I'm confused.  I may wave a card around in the ITMX chamber when I come back later tonight, to see what I can see.  Also, I just misaligned the SRM, and the scatter spots moved.  Now there's just some scatter off of what looks like the BS OSEM holders, as seen through the BS optic.

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