Diffraction calculation of the field in a composite three-mirror unstable resonator

A numerical investigation is made of a two-dimensional model of a composite unstable resonator with three mirrors. The relevant parabolic equations are solved using a three-layer scheme and a fast Fourier transformation algorithm. A strong dependence of the distribution of the intensity of the output wave and of the distribution of the radiation in the far-field zone on the displacement of a reference mirror over distances of the order of one wavelength provides an opportunity for the control of optical characteristics of a system.