Today, we got a ~2kHz bandwidth lock of the YARM with the AO path. We weren't able to turn any boosts on, due to POY noise.
Rana and Koji have written scripts (/scripts/PRFPMI/cm_step and cm_down) that work very reliably.
Here is an OLTF. (Violin filter was off, the crap around 600Hz goes away with them on)
My MATLAB modeling was useful is predicting the features of the loop shape, and the dependence on AO gain/crossover. Still, I need to check it out, because there is nonzero discrepancy between reality and my model (this may be hiding in the non flat MC AO response, i.e. the bump at ~35kHz. Alternatively, the crossover frequency is a free parameter...)
In any case, we have confidence that the CM board is mostly working predictably. We presume that our current obstacle is the very noisy nature of POY, and thus it's not worth spending more time in this configuration.
- Use the CM board to control the Y arm coupled with the PRM. ("PRY"?)
- Determine the game plane for high BW control of CARM.
- Check CM board boosts turn on politely (Transients, TFs)
- Use fast spectrum analyzer to check MC loop gain out to a few MHz. (The bump in the tens of kHz should be fixed / moved higher)
- Think about noise performance of, say, REFLDC, ASDC, RF AS signals, etc. in the PRY case, figure out which one to use first.
- We may want to first focus on directly locking the arm on an RF signal, figure out gains etc. and then figure out how to do DC->RF handoff nicely, or if high bandwidth DC signal control is even feasible.
RXA: we should also use AS45 instead of POY11. It has better SNR and I think our whole problem is too little light on POY.