Reducing the optical load and altering the mode content in the HSURIA axicon resonator

A high concentration of radiation appears near the center of the convex mirror in the HSURIA axicon resonator. In this paper we discuss a method of reducing this concentration by extending the central cone of the W-axicon outward. We describe a more efficient algorithm for three-dimensional diffraction calculations on the field propagation in a cylindrical coordinate system by the stationary-phase method. We investigate the intensity of the highest-Q mode at the center of the convex mirror and the loss coefficient of lower modes of the resonator as a function of the distance which the central cone of the W-axicon extends outward.