Yuhang and Michael

The IR phase shifter position was shifted to the beam waist as per 2435. The arrangement is shown in figure 1, 2. The half wave plate is contained inside the lens mount. We then measured again the noise spectra using the PSD after transmission through the IRMC.

The results show that there is now considerably less change in the noise spectrum when excitation is applied to the phase shifter, versus when there is no excitation. In figures 3 and 4 we show the normalised spectra for pitch and yaw. The X/T and Y/T noise look to have a noise floor of about -30 dB, versus -20 to -25 dB as shown in 2422. The broad peak at ~2.3 kHz also looks like it is suppressed. Figures 5 and 6 show the absolute measurements from the PSD compared to the dark noise. The result is improved versus that in 2407, we don't seem to have mysteriously high pitch noise anymore.