Sheila, Nutsinee

The percentage in the 00 mode power in green had decreased to ~60% from 74% we previously had in the optics lab (alog40594). This is likely due to the fiber swap in chamber causing the pointing to change (10 mode became higher). Sheila tweaked the green alignment on Friday (alog41572). The 00 mode calculated from transmitted power is now 70.8% with the 20 mode being 26% of the 00 mode. The PZT calibration is still ~20V/FSR. The data has been corrected for dark noise and pzt nonlinearity.

The total dips in reflected power including the higher order modes are 49% of the power off resonance. According to the VOPO final design document, the M2 mirror (output coupler for green) is >99.9%. With M1 reflectivity of 98%, modulation depth of 0.094 rad (see alog41622 for the calculation), the measurement suggests a loss of at least 0.3% inside the cavity itself. The input green power into the cavity at the time of measurement was 3.3 mW. The measured power off resonance was 2.83 mW (The BBPD has a transimpedance of 2000 Ohms, a responsivity of 0.2 A/W). That's another 14% loss between the fiber to the refl PD on SQZT6 table. The largest dip without taken higher order modes into account is 35% of the power off resonance. 

From the refl scan we measured the higher order modes to be 14% of the power off resonance, from the trans scan we measured the higher order modes to be 30% of total power. These higher order modes are expected to come back as shotnoise. This discrepancy between refl and trans measurements could be due to the high acoustic noise in HAM6. We should have a much better scan once the VOPO is in vacuum.

The transmitted signal was taken with Thorlabs silicon diode (SM1PD1A) scanned at 1mHz and was monitored through PD concentrator (D1700176 with dual PD amplifier D1200543, a measured gain of 22.4). This seems to give a cleaner data compared to Thorlabs PD100A diode. The refl power was monitored with the BBPD via another PD concentrator PD monitor (D1201349).