An analytical technique is developed for computing mode functions and associated diffraction losses of perturbed multimode optical resonators. It is based upon a consistent field formulation of resonance in an open two-mirror system.
To illustrate the method the theory of confocal resonators is extended to include configurations differing from the confocal case by small geometrical perturbations. This involves computing and expanding a perturbed Green's function for such near confocal resonators. Diffraction losses for certain statistical and deterministic perturbations are computed and related to disturbances arising from an imperfect figure, polish or alignment of the mirrors.
The design and construction of a stable laser spectrometer consisting of a single mode tuneable gas laser and a swept interferometer are described. Measurements of the diffraction losses of perturbed confocal resonators are found to be in agreement with the above analysis.
