At our current crystal position (unoptimized), we have a threshold power of 12 mW. Sheila and Terry measured 7.4-8 mW in March (41150). We can do better with the crystal position.

How I took the measurement:

1) Shuttered the pump, scan the seed to get an unamplified power. I also lowered the seed power going into the fiber coupler hoping to mitigate the crystal heating an green up-conversion.

2) Scan and set temperature for co-resonance (pump shutter opened).

3) Lock the OPO and optimize the non linear gain with temperature while scanning the seed PZT. Record the highest power, repeat for various green input power.

To figure out how much is actually going into the cavity I corrected green refl power (off resonance) for 30% mode mismatch and corrected for 47% intracavity loss found in alog43601. I was hoping that I was wrong about 47% loss but when I tried to propagate pump power from ISCT6 to SQZT6 given the known fiber transmission (alog43166), faraday isolator loss (~4%) and known rejected power the number falls in place with 47% loss. Note to self: forget this. They're not the same thing.

Currently the maximum green power can be sent to the coupler on ISCT6 is 28 mW. The SHG power monitor diode reported ~50 mW. ~20mW is lost between SHG and the coupler. I highly suspect that pointing to the EOM might be bad (faraday in the path has quite a large hole).

When locked OPO at 28mW (-6.2% from a pick off BS to SHG launch PD to be exact) of green input to the coupler the (PZT) pointing was off. The loop was locked to the point where green transmission wasn't optimal. This could not be fixed by temperature alone, PZT pointing  offset had to be adjusted. 

Since we have been operating at a gutless nlg region for pump power this might explain why we haven't been seeing squeezing. Once alignment is fixed on the ISCT6 we should test and optimize OPO loop stability with higher green power along with nominal operating CLF power.