This is a first iteration of a power recycled finesse model of the GQuEST demonstrator.

For this initial version, I have the curved mirror as the input mirror. The ROC is ~20m, which yields a beam size on the end mirror of 2mm. The total length of the power recycling cavity is 4.2m (PRCM1->PRCM2: 1.2m,PRCM2->PRCM3: 1.2m,PRCM3->BS: 1.2m, ArmLength:.6m). A propagate beam call of this system shows the input beam size for this configuration would be ~2.3mm. port_tree.svg shows a map of all the input and output ports of the mirrors and beam splitters (this is less useful but I had been unable to get one of these to work before and thought it was interesting). 

Next, after talking with Sander, I want to find a range of PRM lengths, IFO lengths, and PRM ROCs that yield a beam waist of 2mm on the end mirror. To simplify this idea and to reduce the calculation time, I have merged PRCM1->PRCM2: 1.2m,PRCM2->PRCM3: 1.2m,PRCM3->BS: 1.2m into one length. Then I calculate if my model is stable over a range of ROC values, IFO lengths, and PRM lengths, combining the two lengths into a single power recycling cavity length. PRCgeometrywithcontours.svg is the result. I've included contour lines to see lines of constant beam size on the end mirrors.

I plan on iterating on this but this was a first attempt. For now I have a working model of the single simplified system and a version of the code we can iterate over specific paramaters. Note that for my simplified version an ROC for the PRM of 1.6m (which is what we have in the lab already) is not stable (also 3m is not stable, the size of the existing spares set aside for the LFC, needs to be greater than about 4.5m).