Operating Characteristics of HSURIA Annular Resonator with a W-Axicon and a Rear Flat Cavity Mirror

摘要

In this report are presented the results of tests performed on the half-symmetric unstable resonator with an internal axicon (HSURIA) using a large diameter, closed-cycle CO2 laser facility. The HSURIA used for these tests consisted of a linear W-axicon, a convex spherical feedback mirror and a flat rear cavity mirror. This resonator produced a linearly polarized l = 0 mode of good beam quality. Tests were designed to investigate several critical issues related to the use of the HSURIA with a cylindrical chemical laser, namely, the misalignment sensitivity of the elements, optical effects of support struts, and the feasibility of reducing the high flux on the W-axicon tip by obscuration of the tip. Tests were performed for a variety of resonator configurations with different parameters. The beam quality was rapidly degraded by small angular misalignments of the rear flat but was scarcely affected by much larger misalignments of the feedback mirror. The insertion of strut masks resulted in an unexpectedly large power loss. Analysis indicates that these losses are caused by diffraction effects combined with partial saturation of the medium. A small effective obscuration of the W-axicon tip had little effect on the mode or beam quality, but obscuration diameters with a Fresnel number approaching unity (referred to as the compacted leg length) caused a loss of mode control and a large degradation in beam quality.