The different advantageous embodiments provide an apparatus and method comprising a substrate configured to increase an intensity of light at a desired wavelength. The substrate has a front side, a back side, and an outer edge. The substrate is configured to reflect the light received on the front side of the substrate. The substrate comprises ceramic. The substrate comprises a plurality of sections. The method and apparatus also comprise a material configured to attenuate the light passing between the plurality of sections. The material surrounds an edge of each section of the plurality of sections. The apparatus and method also comprise a cooling system configured to allow liquid nitrogen to be transmitted through the cooling system and receive heat generated in the substrate from the back side of the substrate.