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MIF (General)
stefan.ballmer - 3:47 Thursday 13 June 2019 (9219) Print this report
DRMI work
Yutaro, Masayuki, Terrence, Eleonora, Stefan

- Started with aligning X and Y arm, PRX, BS. The ITMX gave us some trouble with various modes that keep ringing up. Also, the BS RMS is now much quieter.
- We locked the PRMI, extended the roll-off filter for PRCL, MICH and SRCL from a 100Hz pole to a 300Hz pole, and set the UGF: PRCL 100Hz, MICH 80Hz. This made the PRMI very stable again, but
- We noticed clear "mode hopping" glitches in PRCL, together with visible image jumps in the POP camera. They are likely distorsions of the PDH error signal from higher order modes.
- Unfortunately, some of these higher order modes have the effect of INCREASING the POP_RF90_I signal, so optimizing the sideband buildup becomes the wrong thing to do.
- Indeed, when trying to simply "symmetrize" the spot on the POP camera, the mode-hopping glitches were significantly reduces. But the optics RMS is still to high to avoid them completely.

- Next we explored other possible error signals for the PRMI: POP seemed quite clean (RF17_Q to MICH, RF45_I to PRCL, as usual, needs 30 times larger digital gain than REFL).
- With any of those configurations DRMI was not stable, and we only saw short locks. We suspect the mode-hopping glitches are responsible for polluting the SRCL error signal.

We also revived audio for commissioning purposes. The command is

z audio -g 1e-4 -f "zpk([0],[60;4000],1,'n')" K1:LSC-PRCL_IN1

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