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