Diffractive optical elements with modulated zone sizes

The standard design for phase-only diffractive optical elements comprises a transformation of the continuous phase function into a surface relief by m eans of wrapping the phase into regular intervals of M2 pi. This results in a structure with diffractive zones aligned in a horizontal plane. We prese nt an alternative design concept with modulated zone sizes leading to nonpe riodic boundary positions and non-aligned surface structures. The diffracti ve properties are compared to those of conventional diffractive optical ele ments. It can be shown that they are fully equivalent for the design wavele ngth, but exhibit a different spectral behaviour for deviating wavelengths. These properties are exploited for the improvement of the optical performa nce of blazed gratings and diffractive lenses under conditions of deviating wavelengths. Special emphasis is put on the optimization of the ratio betw een diffractive efficiencies of the design order and other orders for blaze d gratings and focusing diffractive lenses, as well as the suppression of i nterference effects within Gaussian beams collimated with diffractive lense s.