Electrically controlled interf erometric aperture stop for a laser resonator

A new type of transverse mode selector is proposed. It is in the form of an interferometric stop representing a tunable inhomogeneous interferometer in which one of the mirrors contains a variable-thickness dielectric layer. A threefold change in the effective size of the interferometric stop is achieved by control with the aid of a piezoelectric ceramic. In experiments on an He–Ne laser this made it possible to vary continuously the number of the transverse lasing modes, select the fundamental TEM₀₀ mode, and excite axisymmetric higher-order modes. Such an interferometric stop could be used in gas lasers with internal mirrors and in solid-state laser resonators where an iris stop would cause difficulties.