jeffrey.kissel@LIGO.ORG - posted 09:33, Monday 11 May 2015 - last comment - 10:23, Monday 11 May 2015(18352)
5 to 5000 [Hz] DARM OLG TF, Take Four
J. Kissel The last few measurements of the DARM open loop gain transfer function have revealed that the DARM coupled cavity pole has gone back down to 270 [Hz] and 260 [Hz] (not posted yet), from where it was at the mini-run at a consistent 355 [Hz]. We're at the beginning stages of tracking this change in frequency dependence "online" by comparing high and low frequency PCAL and DARM calibration lines (and considering adding a few more to increase the precision of the analysis), but until that analysis gets into full swing, I'm taking every chance I can get to measure the DARM OLG TF. Here's another data point. We're in the "LSC_FF" IFO state, with the request input power at 10.7 [W], MICH subtraction ("FF") was ON, but the SRCL FF has a gain of zero (!! -- forgive the file names "FFon," I hadn't actually checked until writing this log). I'll have some more complete analysis (and an answer of what today's DARM coupled cavity pole frequency is) shortly.
Images attached to this report
Non-image files attached to this report
Comments related to this report
I've learned from Kiwamu this morning that the ITM control loops were OFF during the mini-run, and they're OFF now. Unclear if/when Evan & Shiela had them over the course of the measurements. On my list of things to track down during all measurements to see if they affect the DCCP and I can find a pattern: - ITM alignment loops (differential ITM alignment influence is still under suspicion) - ITM/ETM optical lever - TCS power on ITMX (for SRC mode-matching) - Transmitted Arm Cavity power (to track carrier PRC gain) - POP18 / AS90 power (to track sideband PRC gain, and decouple SRC alignment) - MICH / SRCL feed-forward status It's gunna be one heck-of-a detective's adventure. I hope it's fruitful.