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Entry  Mon Jun 17 23:12:19 2013, Manasa, Update, Green Locking, can't get IR to resonate 
    Reply  Wed Jun 19 01:45:49 2013, Manasa, Update, Green Locking, Beat frequency sweep for 3FSR findIR.pngfindIR1.png
Message ID: 8714     Entry time: Mon Jun 17 23:12:19 2013     Reply to this: 8721
Author: Manasa 
Type: Update 
Category: Green Locking 
Subject: can't get IR to resonate 

What I did: 

1. Followed the same procedure to enable ALS (http://nodus.ligo.caltech.edu:8080/40m/8703)
2. Enabling ALS servo stabilized the arm fluctuation and the beat frequency.
3. Beat frequency sweep was done (with ALS servo enabled) by changing offset C1:ALS-BEATX_FINE_OFFSET_OFFSET in steps.

Discussion:

I swept the beat frequency through ~10MHz and could not find IR resonance. But TRY TRX varied from 0 - 0.9 counts as the beat frequency sweep was done. I suspected that the offset steps might have been too big and I had jumped over the IR resonance. So, I repeated the offset sweep again in smaller steps (offset steps 0.1) and it did not help. 
I also played with the gain of the ALS servo to stabilize the loop and set the gain to the maximum (smallest error signal oscillating around '0') and did the frequency sweep. The arm cavity would still not resonate through the sweep but only evolve from no flashes to strong flashes for IR (0 - 0.9 counts).
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