Jenne asked me to simulate the signals on POP QPD when moving different mirrors, as a function of the Gouy phase where the QPD is placed.

I used the opportunity to create a MIST simulation file of the entire 40m interferometer, essentially based on my aLIGO configuration file. I used the recycling cavity lengths obtained from our survey, and other parameters from the wiki page. The configuration file is attached (fortymeters.mist).

Coming back to the main simulation, here is the result, both for the "regular" POP QPD and for a 22MHz demodulated one. The Gouy phase is measured starting from PR2. Cavity mirrors are easily decoupled from PRM in the "regular" QPD. As already demonstrated in a previous simulation, ETMs signals are very small in the 22 MHz QPD. Moreover, it is possible to zero the contribution from ITMs by choosing the right Gouy phase, at the price of a reduction of the PRM signal by a factor of 3-4. Simulation files are attached.

###########################################################################
# Configuration file for full dual recycled 40m interferometer
classname FortyMeters
################################################################ Parameters

# General parameters
const Pin 1             # input power

# Mirror parameters
const T_ITM 0.01384     # ITM transmission [from https://wiki-40m.ligo.caltech.edu/Core_Optics]

###########################################################################
# Configuration file for full dual recycled 40m interferometer
classname FortyMetersPOP_QPD
################################################################ Parameters

# General parameters
const Pin 1             # input power

# Mirror parameters
const T_ITM 0.01384     # ITM transmission [from https://wiki-40m.ligo.caltech.edu/Core_Optics]

% compile and create simulation class
clear classes
MIST('fortymeters_pop_qpd.mist');
s = FortyMetersPOP_QPD(4);

% set angular motion of ITMs, ETMs and PRM
s.ETMX.setMotionShape('pitch');
s.ETMY.setMotionShape('pitch');
s.ITMX.setMotionShape('pitch');
s.ITMY.setMotionShape('pitch');