Right, it's certainly good enough for now and the next months. However there are better opamps available which might give us a better SNR at lower power levels which i would like to try (and replacing opamps is only a few minutes). This would give us the chance to operate at lower power levels with better SNR, which might be useful later.
The error signal size mentioned has been measured with an un-characterized PD from the TNI, where i already mentioned that they are too small but i don't know what's inside the PD. We will check today what we get from the new PD and then either fix/modify the TNI PD or a second PD from LLO (where i have to replace the diode which has a big burn spot)
The PD seems certainly good enough - no need for new pre-amp. With such a high Q resonance, you might be limited by the 1 pA/rHz of the preamp, but if so that's OK.
Error signal size seems too small: for 1 mW and 6 kOhm from the RFPD...