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:
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REFL_A_RF45_I is used
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demod phase = 6.9 deg
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whitening gain = 12 dB
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stage 1 and 2 whitenings are on.
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REFL_A_RF45_I(Q)_GAIN = 0.275
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FM3 and FM4 of LSC-XARM are used. FM3 = p0:z1, FM4 = z41:p1e3.
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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
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Once it grabs a fringe, FM1 boost, p0:z3 can be engaged, MCL can be turned off.
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disabled all the notches in MC2 SUS INF in order to have stable loop.
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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.
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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.
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The X arm trans sum stayed at about 800 counts, seen by ASC-X_TR_A_NSUM