The last time LHO lost lock to this PI was 22nd May 2023. I fetched tape data to derive the observed paramertic gain (R_obs) for that event, and fit exponentials to periods of exponential growth, to get the time constants:
I will take the conservative estimate and take R_obs = 16.
Given an estimate of the mechanical Q factor of 1.7 million, all I need to know is what was the difference between the optical mode frequency and the mechanical mode itself, in order to deduce the underlying Parametric Gain (R0), which would occur at an exact frequency match of these parameters.
To fetch these paramters, I fetched spectra of the OMC_DCPD_SUM (to see optical mode spacing) and MODE28_BP_IN1 (to see exact PI frequency which is demodulated at 80000 Hz). I use the frequency mapping I established earlier for the optical mode to project what the frequency is 2 FRSs away:
- Mechanical mode frequency is 80299.7 Hz, which projects to 5252.09 Hz in the IFO's operating FSR.
- Optical mode spacing is 5250.25 Hz
Now I take these juicy details and I crank the algebraic handle with this simple script.
R0 = 260
