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Entry  Wed Jun 13 02:11:59 2012, yuta, Update, Green Locking, my first modescan (sort of) modescan20120612_1.png
    Reply  Wed Jun 13 02:24:02 2012, rana, Update, Green Locking, my first modescan (sort of) 
       Reply  Wed Jun 13 03:03:38 2012, yuta, Update, Green Locking, my first modescan (sort of) 
          Reply  Wed Jun 13 11:10:56 2012, rana, Update, Green Locking, my first modescan (sort of) 
Message ID: 6810     Entry time: Wed Jun 13 02:11:59 2012     Reply to this: 6811
Author: yuta 
Type: Update 
Category: Green Locking 
Subject: my first modescan (sort of) 

I stabilized Y arm length by using only I phase coarse signal from the beat(C1:ALS-BEATY_COARSE_I_ERR).
I sweeped the arm length by injecting 0.05Hz sine wave from C1:ALS_OFFSETTER2_EXC.
Below is the plot of TRY and the error signal(ideally, Y arm length) while the sweep.

modescan20120612_1.png

I couldn't hold the arm length tight, so you can see multiple peaks close to each other.
We need to
  - adjust offsets
  - adjust rotation phase of I-Q mixing
  - adjust servo filters

to hold the length tighter.

Also, I couldn't sweep the Y arm length very much. I need to calibrate, but to do the modescan for many FSRs, we need to
  - introduce automatic phase optimizing system
There were sin/cos function in the CDS_PARTS, so I think we can feedback I_ERR to control rotation phase of I-Q mixing.

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