Wave-approximation calculation of an unstable resonator with field rotation

An analysis is made of a method for numerical calculation of the parameters of an unstable resonator with field rotation. The wave approximation is used and the three-dimensional diffraction problem is reduced to two dimensions. This makes it possible to analyze the spatial structure of the field for large equivalent Fresnel numbers allowing for the influence of some forms of distortion in the resonator. By way of example, a calculation is carried out of the required precision of the relative alignment of mirrors in corner-cube retro reflectors used in unstable resonators with field rotation.