A method of performing spatial separation of different wavelengths in a single laser cavity includes generating, from a pump radiation source, pump radiations in spatially separate channels and focusing the generated pump radiations in the spatially separate channels towards an active gain medium having amplification spectra. The method also includes emitting from the active gain medium, amplified radiations of the spatially separate channels, each channel of the spatially separate channels representing a corresponding wavelength and focusing the emitted amplified radiations of the spatially separated channels towards an aperture. The method further includes suppressing, at the aperture, an off-axis mode of the amplified radiations of the spatially separate channels, diffracting the amplified radiations of the spatially separate channels received through the aperture to provide diffracted radiations and returning a portion of the diffracted radiations back to the aperture, and collimating the diffracted radiations of the spatially separate channel.

A method of fabrication of laser gain material and utilization of such media includes the steps of introducing a transitional metal, preferably Cr.sup.2+ thin film of controllable thickness on the ZnS crystal facets after crystal growth by means of pulse laser deposition or plasma sputtering, thermal annealing of the crystals for effective thermal diffusion of the dopant into the crystal volume with a temperature and exposition time providing the highest concentration of the dopant in the volume without degrading laser performance due to scattering and concentration quenching, and formation of a microchip laser either by means of direct deposition of mirrors on flat and parallel polished facets of a thin Cr:ZnS wafer or by relying on the internal reflectance of such facets.