I looked a little closer and found what I think are my problems. When I swept the cavity, the reflection dipped down to zero, so PMC is fine.
- I was saturating my PDH sensing PD...I also noticed this when I swept the cavity.
- I noticed that my locked PMC was oscillating at my modulation frequency (280 kHz)...so I added a few attenuators - final count: 13 - 6 - 90 = -83 dBm at laser PZT
- I changed the sign of my feedback. Loop went to uber locked. Is it really possible that I was sitting on the wrong side (the tail) of my error signal?
- Power through is now almost complete. I can no longer see the reflected beam on a sensitive card.
- Measured: 1W transmission (with OPHIR high power meter), 38 mW reflection (with thorlabs meter).