Naoki, Daniel, Nutsinee
Today we increased RF6 from -22dBm to -13 dBm and 8 dBm. We saw excess noise at 8 dBm above 300Hz but no excess noise at -13dBm. REF 12 is the squeezing at -22dB before we started the test. Using the time from alog76553. REF9 and REF10 both show squeezing at -13dBm RF6 at different squeeze angle where one has a better sensitivity at low frequency bucket. REF13 shows squeezing at 8dBm RF6. The excess noise above 300Hz cannot be improved with squeeze angle. Investigation is required.
We turned off ADF sqz angle servo during the test. We readjusted the ADF squeeze angle demod phase and accepted the new value in the SDF.
We are parking RF6 at -12dBm. Since Daniel didn't like the unlucky number 13.
| Loop | Was (-22dBm RF6) | Now (-12 dBm RF6) |
| CLF gain | 10 | 0 |
| LO gain | -7 | -12 |
| FC LSC gain | -2.6 | -0.86 |
| FC ASC gain | 0.1 | 0.03 |
The -22dBm, -12dBm, 8dBm RF6 correspond to 9 uW, 28 uW, 420 uW CLF REFL power.
We rechecked the FDS -22dBm time as the time in the above plot wasn't sqz opitmized to the bucket. Can see in attached plot, CLF at -22dBm and -13dBm have the same SQZ in the bucket, as expected.
Looking back at the past data it seems we may not have adjusted the CLF ISS gain properly during the test causing our sqz level to be stuck at 3dB at kHz region. CLF_REFL_DC was oscillating when RF6 was at -13 dBm and at 8 dBm. This looks like an easy fix and we should try again at some point.
Daniel Nutsinee
Reducing the gain didn't seem to fix the oscillation. We cranked up the CLF power so the RF6 read 6dBm and went out to look at the signal on the scope. We saw 60kHz beat note on the OPO refl and a crooked 105kHz sinewave on the CLF refl. We don't know where the 60kHz beat on the OPO refl came from. We couldn't make any improvement by changing the CLF ISS gain.
After some investigation we realized the oscillation disappeared when we unplugged the RLF. The oscillation came back when the RLF was plugged back in. The oscillation associated with the RLF seemed obvious only when we operated at high power. Next time we try high CLF power again we should attenuate the RLF RF output to the AOM.
The funny thing was PMC refl saw this oscillation as well. We hope this was just an electronics cross talk.
For even higher CLF power with +6dBm at the RF6 demod, we set the CLF servo IN2 gain to-18dB (from 0dB), the CLF ISS gain to 0dB (from 17dB), and the ISS input set point to 2.037 (from 0.347).