Control of transverse laser modes and attainment of the required mode combination

A method was developed for the control of transverse laser modes based on the use of an inhomogeneous interferometer adjusted using piezoelectric ceramics instead of a nontransmitting resonator mirror. Two variants of a device for controlling the ratio of the powers or duration of emission of individual transverse modes were used. Experiments on an He–Ne laser demonstrated TEM₀₁–TEM₀₀–TEM₁₀ mode switching as well as continuous control of the TEM₀₁ and TEM₁₀ modes at an intermediate position; this made possible a symmetric annular distribution of the intensity. Smooth variation of the ratio of the powers of the TEM₀₀ and TEM₀₁ modes, participating simultaneously in the lasing process, was possible. The proposed method could be used to form non-Gaussian light beams and, in particular, a flat-topped beam the profile of which was reproduced during propagation in free space and under focusing conditions.