High-Bandwidth Force Sensing with Optical Cavities

We present two methods for tracking high slew-rate, GHz-amplitude frequency shifts of optical cavities. We are motivated by the use of optical cavities for rapid ($\simeq 10$ kHz bandwidth) sensing of macroscale ($\simeq 100$ N) dynamic forces (e.g. impacts). The first method relies on a Pound-Drever-Hall frequency lock using feedback to a single-sideband modulator to achieve a large dynamic-range with fast locking bandwidth ($> 1$ MHz). The second method uses a dense frequency comb generated by an electro-optic modulator to simultaneously probe a wide ($\simeq 1$ GHz) frequency span.