After Daniel and Nutsinee completed the OPO locking with TTFSS, I re-optimize the crystal position to have higher NLG.

The OPO threshold was double-checked, and it is still around 16~17mW. (Fig1, 74% mode matching)

We did more squeezing and anti-squeezing measurements, plot is shown in Fig2.

• The best we were able to get is 4.4dB squeezing with 9.6dB anti-squeezing as green power 20.3mW going in, NLG=5.7, visibility 97.7%.
• It seems we had systematically less anti-squeezing for this group of measurements.
• Fitting parameters: 65-70% efficiency, 20-50mrad phase noise.
• We still have 15% unknown loss shown. I measured the optical loss on SQZT6 with SEED beam, from before the higher periscope mirror to the homodyne diodes, there is ~2% loss (probable under-estimation due to very large beam size).

More to try:

• Try adjusting the squeezing angle by flipping the sign on the servo board to make sure we go through all the phases.

Automation:

• Add HWP to the SEED path, can borrow from OPO REFL or PSL LO.
• Guardian for squeezing and measurements.