Preparation of random phase plates for laser beam smoothing

Phase plates are required for removing aberrations from laser beams caused by inhomogeneities in the optical components of the laser. The first type of plate that we prepared consisted of a bi-level optical component that caused spatial smoothing of the beam by breaking it up into a fine scale spatial structure. This was made by etching a pattern directly into the substrate using HF/NH{sub 4}F. Components up to 80 cm in diameter were prepared but these are only 85% efficient because of beam losses in secondary maxima. Multilevel designs are more efficient and we have prepared 5 inch diameter samples with 16 levels. These require four separate etch steps but have efficiencies greater than 90%