Following on from alog 42302, I have done an effective bias voltage measurement of ITMY.
The effective bias voltage appears significantly lower for ITMY compared to ITMX:
| V_eff (pitch) [V] | V_eff (yaw) [V] | |
| UR | 10.5 | -3.5 |
| LR | -5.5 | 1.5 |
| UL | 7.5 | 4.5 |
| LL | -10.5 | 1.5 |
Note that the coupling from the signal drive to the optical lever, particularly in pitch, is reduced compared to the ITMX measurement. This is shown in the first attached figure, which shows the signal drive to optical lever transfer function as a function of bias voltage offset. This can be compared with the figure attached to alog 42302.
For these measurements, the ITMY optical lever was quieter than the ITMX. The final two attached screenshots show the ITMX and ITMY optical lever spectra respectively. Red traces (references 0 and 1) are without a signal drive, and blue traces are while driving the LL quadrant at 0.8 Hz, with a large negative bias voltage. The signal-to-noise ratio is much better on ITMY.
