Yuhang and Michael,

We would like to characterise frequency independent squeezing at the best performance we can manage before replacing the OPO. One task is to optimise the alignment of the local oscillator to the alignment mode cleaner, and same for squeezing (i.e. bright alignment beam). Here we checked the alignment of the LO to AMC. We found that the mode matching was still quite good, but there was some undesirable polarization that was leaking. So we added a half wave plate in the LO path just before the homodyne beam splitter. We adjusted the HWP polarization rotation, as well as the tilt and transverse displacement, to remove the unwanted transmission peaks. Then we aligned the LO to reduce higher order modes. The result is shown in figures 1 (TEM00) and 2 (others).

Also we noticed it was quite hot in the clean room. Checking the air conditioning gave a temperature of 25.9 C and humidity 32.8%. Given that it was cold leading up to this measurement we increased the cooling to the cleanroom air conditioner. Some alignment may be affected.