PULSE-FREQUENCY-MODULATED HIGH-FREQUENCY-CARRIER DIFFRACTIVE ELEMENTSFOR PATTERN PROJECTION

An efficient two-stage algorithm is presented for the synthesis of hig h-frequency-carrier diffractive elements. First, an on-axis phase-only stripe-geometry element with an unconstrained profile along each stri pe is designed by an iterative Fourier transform algorithm. In the sec ond stage, a steep linear phase term is added, and the profile is hard -clipped along each stripe. The result is a binary, pulse-frequency-mo dulated element suitable, e.g., for a resonance-domain realization, wh ich permits the elimination of the twin image. Experimental results ar e provided by direct-write electron-beam lithography and optical litho graphy, using both fully and partially coherent illumination.