Previous alogs 50099, 49150, 49067, and 49038.

We are adding the FSS fast feedback path and the common mode control signal which feeds back to additive offset of the mode cleaner servo. The FSS fast follwos the frequency noise model of the free running laser up to about 10kHz, i.e., 10⁴/f Hz/√Hz. Above ~10kHz, the crossover with the EOM path will reduce the signal in the fast path, which was not corrected in the plot.

Around 13.7kHz the gain in the FSS is about 40dB, which explains the coherence seen with IMC controls signal. Since the forrest of peaks are not visible in the FSS fast signal, we conclude that these peaks are getting added after the PMC. The noise between 3 and 10kHz seen by the IMC is not suppressed laser frequency noise, and is still a mystery. The IMC sensing noise is around 10^–4Hz/√Hz. Increasing the IMC modulation depth by 20 would reduce this level by a factor of 10.