kiwamu.izumi@LIGO.ORG - posted 21:37, Wednesday 03 September 2014 - last comment - 09:01, Thursday 04 September 2014(13747)
some settings for locking the infrared laser to an arm
Sheila, Kiwamu,
We locked the infrared main laser to the X arm this evening in order to improve the alignment of the input poointing.
Here are some settings we used for future reference:
- REFL_A_RF45_I is used
- demod phase = 6.9 deg
- whitening gain = 12 dB
- stage 1 and 2 whitenings are on.
- REFL_A_RF45_I(Q)_GAIN = 0.275
- FM3 and FM4 of LSC-XARM are used. FM3 = p0:z1, FM4 = z41:p1e3.
- XARM_GAIN = 0.2. This gave us a UGF of 80-ish Hz according to a kink point in a spectrum of the error signal
- Once it grabs a fringe, FM1 boost, p0:z3 can be engaged, MCL can be turned off.
- disabled all the notches in MC2 SUS INF in order to have stable loop.
- I could not bring the UGF below 40 Hz by reducing the gain. This maybe because of a phase mergin, or not enough supression or perhaps something else.
- SInce the UGF was higher than a vertical mode of SUS_MC2 at 40 Hz, the locking loop kept rinring up this mode. It is visible in the attached dtt screenshot.
- The X arm trans sum stayed at about 800 counts, seen by ASC-X_TR_A_NSUM
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Here is a scren shoot taken last night after the X arm was alinged with green, PR3 was adjusted to get the green transmission onto ISCT1 aligned, and PR2+IM4 were adjusted to get the IR aligned to the X arm.
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