Improved output beam quality in large aperture semiconductor lasers by modification of transverse gain and index profiles

Summary form only given. High brightness, high power semiconductor lasers have attracted considerable attention for applications such as free-space communications and pumping fiber lasers. Most techniques used to increase the brightness of large aperture semiconductor lasers require complex processing techniques and are difficult to realise in mass production. A simple approach is to optimise the performance of conventional broad area lasers (BALs). This has mainly focused on improving the quality of the epitaxial material, thus reducing the tendency for filament formation at high output powers. However, even with uniform active regions, BALs oscillate on many high order transverse modes and suffer from self-focusing and filamentation at high power densities. One way of overcoming this problem is to tailor the transverse gain or refractive index profiles to favour fundamental mode oscillation. In addition, elimination of intense filaments at the laser facet should increase the maximum output power attainable by increasing the catastrophic optical mirror damage limit. We have investigated two techniques to tailor the gain and refractive index profiles in large aperture semiconductor lasers. We have also compared our experimental results with numerical simulations, obtaining good agreement, and indicating that tailoring of the transverse gain and index profiles are very attractive techniques to control the optical field at high output powers in large aperture devices.