Diffractive optical elements for intra-cavity beam-shaping of laser modes

Diffractive optical elements (DOE) are applied as intra-cavity mode selecti on devices for customizing the fundamental mode of laser resonators for hig h power laser systems. Using a phase-conjugating mode selecting element (MS E) in a laser oscillator, we are able to produce a good approximation to a super-Gaussian mode with a near flat intensity profile. This offers higher energy extraction from any following laser amplifiers compared to an unmodi fied Gaussian TEM00 mode. Two different designs for operation in a 1 m cavi ty length Nd: YAG master oscillator are presented. Both designs are surface relief phase elements fabricated in fused silica using photolithography wi th reactive-ion etching to produce 16 level elements for use in transmissio n. One element is designed to replace the cavity end mirror, while the othe r stands off an arbitrary distance from the end mirror. A novel iterated de sign for these transmissive elements is introduced. Numerical results and e xperimental measurements are presented and discussed.