3.6dB squeezing today!

Haocun, Sheila, Terry, Nutsinee

3.6dB squeezing, 6.3dB anti-squeezing, non linear gain = 3, fringe vis 98%.

(screenshot of squeezing and anti-squeezing relative to shotnoise).

Today we balanced the homodyne with 1mW of seed, optimized our fringe visibility (98.5% on PD1 and 97% on PD2). CLF started off at ~10uW, and temperature was optimized for the best non linear gain. We hooked up a spare phase delay to CLF to give us more range of relative phase to play with. With this we got 2.5 dB.

 

Later I went back to check on the error signal on scope XY plot. it wasn't elliptical (more like an elongated stop sign shape). Sheila suggested this was due to saturation. So I lowered CLF power going into the fiber coupler even more until the shape was elliptical. I didn't look at what 3MHz peak looks like. But it was enough to lock both LO and CLF. I probably could have lowered the LO if CLF wasn't saturating the demod board. I didn't check. 

 

We needed more phase delay so hooked up the one for OMC to CLF. So right now CLF phase delay comes from CLF phase delay box, spare box, and OMC box. This gives us a little more than 180 degree (combined with HD). CLF and HD phase delay alone can to a little less than 90 degree.  

 

OPO lock offset is still a problem. I suspect this could be due to the asymmetry cut off of the error signal that probably cuts and crosses zero before the transmission reaches the maximum. This can be fixed with a gain slider in the common path. Still need to find out of this offset is consistent every time or if it scales with power. Then probably let the guardian take care of it in the long run.

 

By the end of the day we ended up with 3.5 dB squeezing. Terry's rough calculation suggested we have a lot of phase noise. It's noise hunting time.

 

Here's the phase delay setting for the best squeezed, anti squeezed measurement:

(squeeze)

(anti-squeeze)

 

Next on to-do list:

- Install 34kHz notch. With this we can push to squash LO noise some more.

- Install the modified TTFSS board to lock mephisto to OPO. 

- Characterize all loops and optimize them for the best noise performance.

Sweet!