Characterization of scattering in an optical Fabry-Perot resonator.

Roughness-induced scattering affects the performance of a resonator. We study the scattering of a single mirror first and compare the result with the losses of a two-mirror Fabry-Perot resonator. Besides some standard tools to characterize the losses, a new method based on the spectrally averaged transmission is introduced.

Transverse mode coupling in an optical resonator.

Small-angle scattering due to mirror surface roughness is shown to couple the optical modes and deform the transmission spectra in a frequency-degenerate optical cavity. A simple model based on a random scattering matrix clearly visualizes the mixing and avoided crossings between multiple transverse modes. These effects are visible only in the frequency-domain spectra; cavity ringdown experiments are unaffected by changes in the spatial coherence, as they probe just the intracavity photon lifetime.

Gouy phase of nonparaxial eigenmodes in a folded resonator.

We study the effect of nonparaxiality in a folded resonator by accurate measurements of the Gouy phase as a function of the mode number for mode numbers up to 1500. Our experimental method is based on tuning the resonator close to a frequency-degenerate point. The Gouy phase shows a nonparaxial behavior that is much stronger in the folding plane than in the perpendicular plane.