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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: 4295     Entry time: Tue Feb 15 03:10:37 2011     In reply to: 4278     Reply to this: 4306
Author: kiwamu 
Type: Update 
Category: ASC 
Subject: IR beam alignment for Xarm : TRX reduction 

I tried aligning the IR beam axis for the X arm to have good beam centering on ITMX and ETMX.

As a first attempt, I started translating the beam upward by steering PZT1 and PZT2, since the pitch was quite off from the center on ITMX.

As a result I could decrease the pitch off-centering down to about 0.5 mm on ITMY, but on the other hand TRX decreased a lot (by a factor of 4).

I am worrying if something in the central part of IFO might be clipping the beam.



When I was touching PZT1 and PZT2, I payed attention on IP_ANG so that I don't lose a beam spot on IP_ANG.

As long as the beam is on the IP_ANG QPD, the angle of the beam should not be so much different.

Each time after I touched the PZTs, I realigned ITMX and ETMX to maximize the transmitted light.

In this way I proceeded the alignment by changing the PZT offsets little by little while keeping the X arm locked always.

At the beginning, all the PZT offsets were zero. And at the end of this work they became:

 C1:LSC-PZT1_Y = 1.880

 C1:LSC-PZT2_Y = -1.699

But during this alignment work TRX gradually decreased eventually down to 0.25, which had been 1 at the beginning (TRX is calibrated by dividing it by its maximum power).

Along with this TRX reduction, I found that the optical gain also decreased by a factor of about 5.

This fact has been confirmed by intentionally increasing the filter gain such that the servo oscillates at the UGF.


The amounts of the X arm's beam off-centering have been measured by the A2L technique.

     - ETMX

         PIT  = -1.61 mm

         YAW =  -0.918 mm

    - ITMX

         PIT = -3.76 mm

        YAW = -2.24 mm


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