Naoki, Sheila, Elenna
We tested high NLG. We increased the OPO trans power from 85uW to 105uW, which corresponds to NLG of 22.7 and generated squeezing of 18.3dB according to the NLG calculator. We measured sqz/asqz with high NLG as shown in the attached figure. The squeezing above 1 kHz slightly improved, but the squeezing below 500 Hz got worse.
At 1kHz, squeezing is 3.6dB, mean squeezing is 13.5dB, and anti squeezing is 16.7dB.
We suspect that the degradation below 500 Hz is due to the SRCL detuning so we tried to change the SRCL offset. When we changed the SRCL offset from -175 to -150, squeezing below 500 Hz slightly improved. So the degradation below 500 Hz is likely due to the SRCL detuning. We also tried the SRCL offset of -125 and -100, but they are almost the same as -150. Everytime we changed the SRCL offset, we adjusted the sqz angle to maximize the squeezing at high frequency.
How to increase the pump power
- original SHG launch power is 23.1 and SHG rejected power is 4.9 with ISS
- request OPO guardian to LOCKED CLF DUAL NO ISS
- rotate HWP to minimize the rejected SHG power
- change the ISS drivepoint from 5 to 3 to keep the ISS control monitor around 3. The SHG launch power reached around 28.
- change the ISS setpoint in sqzparams to 105, load the OPO guardian, and request OPO guardian to LOCKED CLF DUAL
To be clear: we did not change the current SRCL offset permanently. But we would like to reduce it to at least -150 for the reasons stated above. Tagging CAL as they are the main group we thought of in regards to this change.