Well, 3.969 but I'll call it a 4. Anti-squeezing 7.6 dB, nonlinear gain 3.6, fringe vis presumably 98%. I didn't adjust.

I haven't had a chance to give Haocun's code a try so here's a screenshot from SR785. I like SR785...

I also double checked the 3MHz error signal before the demod. Even at  <10uW CLF the signal looked like it was nearly at saturation (peak to peak was only ~300-400mV).

OPO offset shenanigans

Today I spent some time investigating the offset issue that causes OPO to lock at its suboptimal place. Because of the asymmetry cutoff when we operate at relatively high green power (~3.5-4mW into the cavity) the error signal would cut off and crosses zero before the transmission reaches optimum. As mentioned in another alog the common offset slider bar can be used to put the OPO in the right place. However, the success rate of doing this seemed to be depended on what temperature and what green power we're operating at. Given 20 mW going into the fiber coupler (corresponds to about 4mW into the OPO), at below and above phase matching temperature (arbitrary set to 33.5 C and 34.5 C) I can lock with an offset without issue. At phase matching temperature (33.88 C) it took me three attempts. This test was done at the same green input power and same gain setting with seed/clf blocked. I also noticed that when I switched from seed to CLF after a nlg measurement the lock point of the OPO went back to the suboptimal place. It seemed to be very sensitive to temperature, that makes nonlinear gain measurement and optimization challenging (OPO did jump back to its suboptimal place a few times during nlg optimization, but it was possible to optimize, so I think our nonlinear gain measurement has been correct). Note that the amount of offset from optimal lock point did change with pump input power. The higher power, the more offset.

With OPO locked at the highest power we can throw into the fiber (20 mW). nonlinear gain of 3.6, I went and took another squeezing measurement. That's how we ended up with 4dB (maybe that new LO notch filter helped a bit, but probably not as much as increasing the pump power). I did not check the balancing or the fringe visibility since we still got the same amount of squeezing this morning compared to last night I thought the alignment must have not drifted much.

To get more squeezing at this point we will have to optimize our green transmission from ISCT6 to HAM6 feed through. Last time Haocun checked we were down from 76% transmission to 52% transmission. 

*random thought* maybe it's worth looking into one of the view ports to see that we don't have green scattering/clipping. I don't know why would nlg dropped from 15 in air to 5 in vac. The green beam on the camera also doesn't look that round. Although that could just be the band pass filter in front of it.

Also I left the green input power to fiber coupler at 20mW. I didn't adjust the gain in OPO guardian so the auto locker won't work at the gain set by guardian (-9dB). The gain needs to be -24dB and the first boost can't be turned on.