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). |