[Rana, Jenne, Yuta] (late last night)
After some trouble getting the PRMI to lock with REFL55 I&Q last night, we began to think about the size of signals everywhere, and the coupling of the sidebands in the different cavity configurations. We have determined that it is possible that the Q phase signal is too small everywhere, so the PRMI will never be easy to lock. The Q phase will be smaller than iLIGO equivalents since the modulation frequencies are lower, and we have a small Schnupp asymmetry. The calculations of signals at each port were all done for the DRMI case, where sidebands get recycled more, so signals get larger. If locking the PRMI is "hopeless" due to very small signals, we should stop trying, move on with other things, and come back to the corner when we have the DRMI ready. In order to figure out if it is reasonable to keep working on the PRMI, we must calculate the size of all of our signals at each port, and convert them into real units (if we expect a 1mVpp signal at REFL11Q, we're not going to successfully lock MICH with that).
So, we should:
* Calculate sideband signals at AS and REFL, for 11 and 55 MHz, for the PRMI case.
* Convert those signals into physical units (Watts -> Amps -> Volts).
* In parallel, work on dual arm ALS, and FPMI locking.
* Try using ALS CARM for frequency stabilization.
* Hand off from ALS CARM and DARM to PSL.
* To do ALS-FPMI, we should:
* Use A2L to center the IR spots on all arm cavity mirrors.
* Align green beams to the arms.
* For each arm, determine which frequency (arm green or PSL green) is higher.
* Lock the arm in green, align Beat PD.
* Push ETM, watch beat in the phase tracker.
* Repeat for other arm.
* Use ALS input matrix to construct CARM and DARM signals.
* Check by shaking ALS-CARM, watch both X and Y beat signals - if they move in the same direction, we were right, but if they move in opposite directions we have flipped CARM and DARM.
* Send the ALS-CARM signal to MC2, or the analog common mode board.