After Richard turned on the squeezer high voltage I went to the LVEA and did a few characterization measurements on the squeezer.
- The first two attachments are the green transmission and reflection as we scan the OPO PZT, we have the asymmetry caused by self locking from large absorption, so I also did a scan with low green power (1.9mW at the fiber launch diode). We still see only 2 green FSRs for 80V of range on the PZT, the 01 peak is about 10% of the 00 peak for green. The reflected power on resonance is 20% of the reflected power off resonance.
- I updated the calibration of the green fiber launch PD, and the green OPO REFL diode, based on measurements with a power meter. I also checked the calibration of the seed launch diode, but didn't update it since it is within 10% of correct.
- We are getting less seed power transmitted through the OPO than we were in the past for the same seed launch power. I quickly touched up the alignment into this fiber, but I only got a small improvement in transmission this way. The OPO guardian sets the seed launch power in the state PREP_LOCK_SEED_LOW, it was set to send in between 1.5mW and 0.5mW according to the launch diode. This wasn't giving us a high enough red transmission to trigger the OPO locked, so I changed this to 1 - 3 mW for the nonlinear gain measurements. The first time that this state ran, it moved the half wave plate all the way through so that the maximum seed power was injected into the fiber. Since we do not want to inject more than 50mW into this fiber, I edited the code to close the flipper before adjusting the wave plate, and open the flipper once the power is in the correct range.
- I locked the OPO at several different powers to measure nonlinear gain. For each power level, I adjusted the OPO servo gain to keep the ugf near 1kHz, but I haven't adjusted the gain in the guardian yet.
- The pdf attachment shows the threshold measurement. The threshold is around 30mW of power incident on the OPO (based on a measurement of the reflected power with the OPO off resonance), very similar to the threshold that we had in May. With 19.5mW into the fiber (the max we are willing to launch is 20mW) we get a nonlinear gain of 4.3 which is a normalized nonlinear interaction strength (x) of 0.52, compared to a max nonlinear gain of around 2 before the fiber swap.