[Torrey, Ian]

We added a variable inductor in series with the EOM to make a resonant LC circuit (tank circuit as Lee called it) to boost the phase modulation used in the PDH locking of the filter cavity. This should increase the modulation depth at the frequency f = 1/(2*pi*sqrt(LC)). The EOM capacitance can be found on the thorlabs website with a value of 14pF. Solving this equation for our current modulation frequency gives roughly 700 nH inductance required. We have a box of variable inductors in the lab. We put one of these in and tuned the inductance to maximize the error amplitude. This gave a 3x boost to the error amplitude, while the loop still provided the same amount of supression. This gives a ratio of the error amplitude to RMS of the cavity lock of 230mV/14 mV of ~16. This should be sufficient now to swap out to the good diachroic mirrors.