604 thereby preventing the element 604 from bending under thermal load in the embodiment depicted in fig6 the reflection diffraction element 604 is formed on a substrate with a high heat conductivity and a low coefficient of thermal expansion for example the reflection diffraction element 604 may be formed from a substrate made of diamond sapphire or a glass ceramic such as zerodur the backside thermal management element 620 may be made out of a material with high thermal conductivity e g copper the backside thermal management element 620 further has cooling channels 621 the cooling channels 621 may be filled with a liquid with a high specific heat such as water the cooling channels 621 transport heat generated at the reflection diffraction element 604 and transmitted into the backside thermal management element 620 away from the reflection diffraction element 604 one of skill in the art will appreciate that the cooling system depicted in fig6 and described herein can be used with a variety of reflective optical elements depicted in the preceding figures for example a backside cooling element such as the backside cooling element 620 could be used with the first and second reflective diffraction elements of fig1 and 4 as well as with the reflective diffraction elements of fig2 and 5 a first component of the external resonator arm input 602 emerging from the reflection diffraction element 604 is a diffraction of the resonator arm input 605 that constitutes a system output 605 the system output 605 is composed of a plurality of spatially and directionally overlapped single wavelength beams emitted from the plurality of emitters of the laser source 601 the spatial locations of the laser source 601 the position to angle transformation element 603 and the reflection diffraction element 604.