f2f meeting peculiar feature at the FSR

Investigating fsr feature for lower PSL values

Numbers 1.9W into MC (noise level ~ 2.5*10-1 cts/√Hz) f(kHz) 37.81 37.97 38.01 38.06 38.08 cts/√Hz 1.97 1.72 0.84 6.82 0.58 f(kHz) 37.81 37.97 38.01 38.06 38.08 38.10 cts/√Hz 12.22 5.06 4.71 14.69 2.80 2.70 ratio2-1 6.2 2.94 5.6 2.15 4.83 f(kHz) 37.81 37.97 38.01 38.06 38.08 38.10 cts/√Hz 15.21 10.61 4.68 26.91 2.55 5.32 ratio3-1 7.72 6.17 5.57 9.95 4.40

Fit at f=37.81kHz G(f) =N/(1-f2/f02 + i Q f/f0) where, N a normalization factor f0 a resonance Q the quality factor at f0

Some (crazy?) thoughts To improve modeling of the internal mass resonances and their contribution to the signal one could do: Mirror excitation transfer function measurements to identify which resonances are contributed by which optics Ring-down measurements on each resonance for a more accurate measure of the resonance frequency and Q Finite element analysis modeling of the optics to determine the mode shape of the pertinent resonances and a comparison between theory and experiment