stefan.ballmer@LIGO.ORG - posted 00:26, Friday 24 January 2014 - last comment - 02:42, Friday 24 January 2014(9521)
10Watt
Kiwamu, Stefan We increased the input power to 10Watt. - We removed the lock from the rotational stage interlock. - We rotated the Laser Power rotation stage from 56.1 to 30deg, raising the power by a factor of 10. - The power levels IMC REFL and IMC WFSs were kept thge same by adjusting the lambda/2 rotation stage on IOT2L. We had and have 12mWatt on IMC REFL. - We reduced the analog electronic gain on MC TRANS by a factor of 10. - We verified that we now have 29.7mWatt on LSC-REFLAIR_A, and 30mWatt on on LSC-REFLAIR_B on ISCT1. - We confirmed that the IMC UGF is still 54kHz. - We updated the IMC Guardian to switch on all 3 stages, and increased the in-lock gain to 13dB. This left the phase margin at 26deg.
Because the MC2 TRANS signal was not showing healthy signals probably due saturation in the analog chain, the guardian wasn't capturing a fringe with the trigger. So we changed the guardian script such that it looks at IMC-TRANS instead which is not saturating. The threshold is now set to be 500 counts. This seems working so far.
Here is another plot which is related to the crossover adjustment. There was a unwanted crossover bump at 20 Hz before the adjustment.
Blue curve: before the adjustment
Red curve: after the adjustment
Green curve: during the adjustment.
Another plot: OLTF of IMC after the power increment. As expected, the OLTF didn't change at all by the power increment.
Note that it might be too aggressive because of a shoulder at 200 kHz which is kind of close to the unity gain. If it turns out that this is not good, we can always disengage the boosts and decrease the UGF a little bit.