Dan, Koji

We came in on Sunday and worked on several measurements on the OMC.

1) OMC breadboard mode

In the measurement the other day, we observed the forest of the peaks beween 400 and 1.3kHz.
There should be a peak from the OMC glass breadboard. We tried to identify the mode by exciting
the OMC SUS. We did not find any clear sign of the resonance below 990Hz, which was the frequency
limit of the excitation in the OMC SUS model. There is some possibility that the mode exist at higer frequency.
The experiment at Caltech showed the resonance at 1.1kHz with some different boundary condition.

We also tried to replicate the noise structure by shaking the vertical motion of the OMC SUS. This was
not successfull as Zach indicated before.

2) Effect of the OMC ASC noise

The OMC ASC control was done by the OMC QPDs. We checked if turning off the servo cause any improvement
or deterioration of the OMC length noise. We observed no difference in the half fringe spectrum of the OMC length noise.

Right now the OMC dither alignment control is not functional partly because of degraded RIN of the IMC trans.
The RIN of the IMC transmitted beam was 10^-5 to 10^-6. There was modification of the IMC WFS servo recently, and
this might be the reason.

We also checked if we can see any OMC length noise by injecting a peak in the OMC tip-tilt angles. There is some coupling
but the result was not so conclusive.

3) Direct measurement of the OMC PZT driver noise

In order to try to pin down the actuator noise contribution in the OMC length spectrum, the outputs of the PZT driver
were measured. First of all, the HV power supply voltage was reduced from 100V to 10V for safety. A DB25 breakout was
inserted at the PZT driver output so that we could measure the voltages across the PZTs. The measurement result is going
to be summarized in another alog entry.

The output of the HV voltage supply was restored to 100V after the measurement.