Parameter	Value	Virgo value	Difference
Power recycling cavity length	11.953 m	12.053 m	-0.100 m
Input mode cleaner length	143.434 m	143.573 m	-0.139 m
Schnupp asymmetry	0.04 m	0.878 m	-0.838 m
Distance BS-IMX	5.993 m	6.512 m	-0.519 m
Distance BS-IMY	5.953 m	5.634 m	+0.319 m
Distance BS-PRM	5.980 m	5.980 m	+0.000 m
SB1 modulation frequency	6270339.2 Hz
SB3 modulation frequency	8360585.6 Hz

The possible sets of SB2 modulations and signals recycling cavity lengths, in order to have SB1 simultaneously resonant in PRC and SRC are:

Modulation frequency [Hz]	SRC lengths [m]
56433952.727	10.62454227	13.28067783
68974831.111	10.86600914	13.03921096
81515709.495	11.03317851	12.87204159
94056587.879	11.15576938	12.74945072
106597466.263	11.24951534	12.65570476
119138344.647	11.32352531	12.58169479
131679223.030	11.38343814	12.52178196
144220101.414	11.43293135	12.47228875
156760979.798	11.47450565	12.43071445
169301858.182	11.50992079	12.39529931
181842736.566	11.54045108	12.36476902
194383614.950	11.56704198	12.33817812
206924493.334	11.59040974	12.31481035
219465371.717	11.61110691	12.29411319
232006250.101	11.62956653	12.27565356
244547128.485	11.64613287	12.25908723

Finesse simulation

The 81MHz modulation frequency has been chosen to set up a Finesse simulation.

The Finesse input file: advirgo_lmod_ss_11m.kat

Input power (before power recycling mirror) is 100 W.

The correct resonance conditions of all sidbands have been checked. Here are the results.

Arm cavity resonance

The signal and power recycling mirror have been removed and the north cavity length changed over one free spectral range. Here is the transmitted power.

Power recycling cavity resonance

The arms are kept on resonance for the carrier, the signal recycling mirror is removed and the power recycling cavity length swept over one free spectral range. The beam splitter pick-off power is shown here:

Transmission to anti-simmetric port

The signal recycling mirror is remove, the power recycling cavity and the arm cavities are kept on resonance, MICH is swept over one free spectral range. The anti-symmetric port power is shown here:

Signal recycling cavity resonances

Arms and power recycling cavities are on resonance, MICH is tuned to dark fringe, the signal recycling cavity length is changed over one free spectral range around the RSE value of 0 degrees:









































As expected at the operating point:

• SB1 is close to anti-resonant in the arms, resonant in the PRC, has small transmission to ASY and it is anti-resonant in SRC
• SB2 is close to anti-resonant in the arms, resonant in the PRC, has significant transmission to ASY and it is resonant in SRC.
• SB3 is not resonant in arms, not resonant in PRC, has small transmission to ASY and it is not resonant in SRC