Terry Nutsinee Haocun Sheila Fabrice
We believe that the first dichroic used to separate the squeezed beam from the reflected green light from the OPO is mounted backwards, and that this a likely explanation for the extra losses seen with homodyne measurements 43948.
Nutsinee and Daniel locked the OPO this morning, Nutsinee will add more information about that. We tuned the temperature to have co-resonance without nonlinear gain, we found the third co-resonance away from phase matching at 41.5 C, but still had some nonlinear gain. We went to the 5th co-resonance temperature, 51.15C. Once we had ZM1 aligned and increased the seed power injected to 14 mW measured at the seed launch PD we had a nice beam to use for the loss measurement and alignment checks.
When we started to measure powers in the transmitted seed, we saw that there were three beams, and that these beams were indeed seed light not green. We measured 330uW of seed right after the first dichroic, the three beams get closer near the second dichroic but are separated enough by the time they reach the Faraday rotator that only the center one passes through the rotator, where we measure 270uW, or 80% of the light. This dichroic is E0900491.
Other things done today:
We measured the green power transmission into the chamber as 44%. Fabrice was happy, so we are happy
| before coupler on ISCT6 | 14.1mW |
| out of collimator in HAM6 | 6.23mW |
Fabrice + Kyle torqued the feedthrough. We also added one more peek cable bracket the routing of the new fiber. We did this because when we plugged in the new fiber we did not route it under the dog clamp that the ordinal fiber was routed under on the east side of the table, which made Fabrice concerned about rubbing in the loop that the fiber makes to avoid shorting the isolation.
Glad you figured that out!
The overall throughput of the fiber chain is probably the new best in the history of green fiber science, so I am also happy. Let's hope it stays that way.
Here's a couple of photos of the beam coming off the backward dichroic. The first picture was the beam reflected off the first dichroic (closest to the OPO). Note that if you block the green and just look at the seed the red beams are right on top of the green. The second photo is after the 2nd dichroic mirror, just before the polarizer.
Note on OPO locking
Attached a spectrum, a transfer function, and the settings that worked. We locked the laser to the OPO just like how we have been doing but using PZT only. We had much stronger purged air than the last time (April vent) when we locked in-air successfully so the purged air has to be turned down. The UGF was ~22kHz with roughly 20dB gain at 1kHz, and no boosts were on (2nd boost in the common path can be turned on unreliably).