Transverse profile shaping of laser beams by means of aspherical mirror resonators

Two main approaches exist in order to generate laser beams with transverse profiles which depart from the common Gaussian shape: The use of graded transmission resonator mirrors and the use of aspheric mirrors. Aspheric, fully reflecting mirrors have the advantage of better power and energy handling and availability of reflecting surfaces at wavelengths where transparent materials are inconvenient to handle and eventually nonexisting. A beam synthesis method was developed by means of which it can be proven that any pre-required beam profile can be supported by a resonator based on either variable transmission mirrors or aspheric mirrors, in the empty-cavity approximation. The cavity will not however necessarily support the pre-required mode as the lowest-loss mode, and the gain profile of the amplifying medium has to be taken into account. Examples will be presented in which cavity design improves the efficiency of the laser by coupling between the mode profile to the gain profile of the medium. Additional applications of aspheric mirror resonators include the matching of free-space modes to waveguide modes and shaping of beams according to subsequent beam' handling requirements like focusing to preferred spot shapes for materials processing.