From 2023-12-28

Yuhang, Hsien-Yi, Michael

The goal of this day was to properly characterize and set up the squeezing/antisqueezing scan for taking the data for Taiwan's machine learning project. From the squeezing vs power data that was taken previously, it seems we can only go up to about 47.5 mW injection before the data becomes less meaningful.

We send a scan signal to CC2 Perturb in but the error signal becomes quite noisy. It was sent to an SR560 (although it's just in low noise mode, DC coupling, 1 gain - no filtering is selected). While inspecting the output of the homodyne time series in DGS, we suspected there was some DC power being amplified and deamplified inside the OPO. Perhaps it is backscattering of the LO from the homodyne detector into the OPO (a recurring issue). We wanted to look at bit further back but get 'synchronization error' in dataviewer. This must be improved with the installation of new DGS. Anyway, we saw that the possible scan range of CC2 phase without unlock is somewhat low, so we decided to check visually if it covers squeezing and antisqueezing. We sent a constant voltage at several points from -10 to 10 mV to CC2 Perturb In and checked the homodyne spectrum in diagguie, where the electronic and shot noise levels were saved last time. We managed to set the homodyne angle to a good point where we can start just before peak antisqueezing and end just after peak squeezing. Also in DDS 40 degrees homodyne corresponds to squeezing while 90 degrees corresponds to antisqueezing. A bit odd.

So we confirmed the feasibility of the squeeze anti-squeeze scan and were ready to leave it and take data. Considering that the fitting previously also showed large optical loss, we decided it would be good to optimize alignment of BAB (squeezing) and LO to alignment mode cleaner (i.e. homodyne). But we ended up taking data at 25 mW green injection for about half an hour.