Thin-film selector in a spherical resonator

A theoretical analysis was made of the longitudinal-mode losses in a laser with a spherical resonator and an absorbing selector film as a function of the resonator length, the radii of curvature of its mirrors, the Fresnel number, the position of the selector in the resonator, and the conductivity of the film. Optimal (from the point of view of the losses) resonator configurations were found taking into account the diffraction losses and those in the selector. Single-frequency stabilized lasing was achieved experimentally with accurate tuning of the radiation wavelength in an He–Ne laser by a ceramic resonator and automatic control of the relative position of the selector and a resonator mirror.