Swept-frequency induced optical cavity ringing

A characteristic ringing has been observed when a high finesse ring cavity is excited by an external laser source. It is caused by the beating between the laser frequency and the cavity mode frequency when either is swept in time. The temporal waveform is analysed theoretically, extending similar analyses of ocean waves and of superconducting cavities to the optical case, and can be brought into good agreement with the experimental waveforms provided the effects of nonlinearities in the relative frequency scanning rate and of the finite laser linewidth are included. This gives a novel determination of the finesse F of supercavities (where F∼104), and permits the determination of a laser linewidth less than that of the cavity resonance.