Sheila, Camilla. WP#12573
Sheila and I realigned the Homodyne after it needed to be touched to re-seat one of the PDs in 85116. Sheila balanced powers using the LO waveplate and measured visibility to be 98.4% (11.4mV min 1.46 V max).
We then used SQZ_MANAGER SQZ_READY_HD (needed to change LO gain, see sdf). Attached plot.
Last done by Kevin/Vicky in 84661, they got 6.4 to 7 dB of SQZ, 14.6 dB of anti-SQZ, and 12.1 dB of mean squeezing.
| Type | NLG | Angle | SQZ (@300Hz) | DTT Ref |
| LO shot noise | N/A | N/A | Used as 0dB | ref 1 |
| ASQZ | 10 | (+) 204 | 14.3dB | ref 2 |
| SQZ | 10 | (-) 114 | -7dB | ref 3 |
| Mean SQZ | 10 | N/A | 10.7dB | ref 4 |
| OPO Setpoint | Amplified Max | Amplified Min | UnAmp | Dark | NLG | OPO Gain |
| 95uW | 0.0530 | 0.001913 | 0.005307 | 9.1e-5 | 10.16 | -8 |
After Sheila and Camilla realigned the homodyne, I tried estimating the NLG by looking at the ADF beatnote while varying the squeezing angle to map out the ADF-LO ellipse as described in the ADF paper.
The channels used to measure the beatnote were H1:SQZ-ADF_HD_DIFF_NORM_{I,Q}. The squeeze angle was varied by sweeping H1:SQZ-CLF_REFL_RF6_PHASE_PHASEDEG from 0 to 275 degrees with both polarities of the CLF servo (H1:SQZ-CLF_SERVO_IN2POL).
I then fit the data to an ellipse. The ratio of the semi-major to semi-minor axes is denoted by G in the ADF paper and was then used to compute the NLG. This results in
G: 5
NLG: 8.8
By comparison, an NLG of 10.2 is equivalent to G=5.4, which is consitent with the accuracy of this data. This kind of measurement could probably be improved in the future by taking more data near the anti-squeezing points on the ellipse.
It's not obvious from the ADF paper how to convert from G to NLG and back. For posterity, the functions I used for these conversions are also attached. These use the "alternative OPO configuration" shown in Fig 6(a) of the ADF paper.
The data is located at /ligo/gitcommon/squeezing/sqzutils/data/NLG_HD_06_24_2025.h5.
