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Entry  Sun Feb 13 15:02:23 2011, kiwamu, Update, Green Locking, X arm beam offcentering has been measured misposition.png
    Reply  Tue Feb 15 03:10:37 2011, kiwamu, Update, ASC, IR beam alignment for Xarm : TRX reduction 
       Reply  Wed Feb 16 02:04:11 2011, kiwamu, Update, ASC, IR beam alignment 
Message ID: 4306     Entry time: Wed Feb 16 02:04:11 2011     In reply to: 4295
Author: kiwamu 
Type: Update 
Category: ASC 
Subject: IR beam alignment 

[Jenne and Kiwamu]

 This time we aligned the vertical angle (not the translation) of the IR beam so that the transmitted light from BS shoots the center of ETMY.

The idea is to use ETMY as a beam pointing reference instead using IP_ANG, assuming the translation is not so bad.

As a result it looks like we are wining. A quick A2L test on ITMX_PITCH showed a small off-centering at sub-milimeter level.

 

 We are concluding that the initial beam after PZT2 had been pointing downward somehow.

Before doing this whole job, we checked the spot shape on IP_POS to see if the beam is clipped or not. It was a round shape, which means no clipping around MMT.

But on the other hand, the spot on IP_ANG had been clipped more than half of its bottom as Suresh reported on his elog (see here).

I found that this clipping is able to be fixed by moving the beam angle upward. I guess the clipping happened at one of the steering mirror in the ETMY chamber.

According to these information, we imagined that the beam was somehow pointing downward after PZT2.

So we started aligning the beam by touching only PZT2 for vertical direction. Then we found a beam spot on ETMY's suspension frame, and brought it to the center.

Then we aligned BS and X arm for this new beam axis. The it resulted a small off-centering on pitch.

Once the MC fully gets back, we will examine the TRX degradation with this configuration.

ELOG V3.1.3-