Marc, Yuhang

We found that one SR560 that was used for the input oplev yaw was broken (increasing a lot the noise above 10 Hz) so we replaced by the one used for the length sensing oplev.

We want to find the good PSD position and first tried to measure the natural length mechanical resonance in the tilt PSD without excitation but we could not see any signal at the expected frequency (0.94 Hz).

We decided to inject white noise in the length of INPUT at this frequency.

First we used 5000 counts amplitude but we could see harmonics so we decreased the amplitude to 1000 counts.

The attached figure report the 0.94 Hz peak amplitude in the pitch and yaw spectrum while moving the tilt PSD (larger position correspond to moving the PSD closer to the INPUT mirror).

For the yaw, we can see the expected 'V shape' in addition to some constant noise which might be due to non perfectly decoupled driving.

The minimum of this 'V shape' is at about 7.3 cm which is really close to the waist position.

For the pitch, we can clearly see the 'V shape' but the minimum position is about 3 cm which seems to be really off.

We have to investigate the reason for this discrepancy.