GRAY-SCALE MASKS FOR DIFFRACTIVE-OPTICS FABRICATION .2. SPATIALLY FILTERED HALF-TONE SCREENS

Fabrication of diffractive optics with binary masks requires multiple photolithographic processes to produce efficient, continuous profile e lements (kinoforms). Alignment or etching errors at any stage of fabri cation decrease the efficiency of the element. We developed two access ible procedures that minimize fabrication complexity, component turnar ound time, and cost. The first technique [Appl. Opt. 34, 7507-7517 (19 95)] uses gray-scale masks produced by commercial slide-imager systems . Here, we report on an alternative technique for producing gray-scale masks by spatial filtering of halftone screens. Using the photoreduce d gray-scale patterns as lithographic masks, we fabricated diffractive -optic blazed gratings and lens arrays in both photoresist and quartz. First-order efficiencies as high as 70% are reported. Also, the stren gths and limitations of this technique are compared with the previousl y reported slide-imager method as well as other fabrication methods.