Tonight, I wanted to stick with the simple Michelson in order to make sure that the mirror motion is not too crazy in the Michelson degree of freedom.

It seems that the motion tonight is quitter than last night. According to some spectral analysis, I am concluding that the MICH is as quiet as it used to be, compared with this winter.

However, I found another issue -- the RF phase changed between the noon and tonight for some reason. This seems to be related to the electronics at ISCT6 and/or the rack by ISCT6.

(MICH)

Tonight, MICH was quiet. I did not see large angle excursion. The dark port DC light stayed mostly below 15 counts and sometimes reached 20 counts and 4 counts at the highest and lowest respectively in ASAIR_B_LF. Since the bright MICH light was about 1400 counts, these numbers did not seem too crazy. Note that I observed the DC light fluctuating as big as 160 counts in this noon. Probably due to some installation activity by ITMX and also due to the BS oplev issue.

I have calibrated the error signal by doing the same old free-swinging scheme. The peak-to-peak in counts were 984. Using this infromatin and knowing the UGF, I calibrated the error signal into meters.The noise level of MICH is consistent with that of the past PRMI commissioning (see for example alog 10472).

(RF phase changed)

As soon as I started locking MICH, I noticed that there was large I signal in ASAIR_A_RF45. This was very strage. To get the signal maximized in Q, I had to rotate the demodulation phase more than 90 degrees. I ended up with 14 deg which used to be -91 until this noon. The readout gain seemed the same according to a comparision between today's and yesterday's open loop transfer functions. I have no idea of what happened. I briefly checked the RF cables by the ISCT6 to see if there is a loose connection somewhere, but I did not find a suspicious point.

I then checked the demod phase of REFL_A by locking PRX. REFL_A did not need to rotate the demod phase at all. This means the phase change is a local issue in ISCT6 and its electronics racks. I will take a close look tomorrow.