Interference effects in diffractive beam shaping elements

Abstract

An increasing number of commercially available and proprietary design algorithms based on scalar or electromagnetic theory allow the calculation of a large variety of diffractive optical elements (DOEs) with excellent performance and high diffraction efficiencies. However, micro-structuring technologies used for the fabrication of DOEs have tolerances and limitations that reduce the measured diffraction efficiencies to below the theoretical values. For some applications not only the absolute value of the diffraction efficiency is of concern, but at least the same importance has to be paid to the spatial distribution and the optical effects of the stray light. Collimating and beam shaping elements are typical examples for the latter case. Due to interference effects with the "signal beam", very small amounts of stray light can already reduce the optical performance significantly, e.g. characterized by an irradiance uniformity. Especially for applications with beam shaping DOEs in micro-systems these effects get more critical since the short propagation lengths do not allow a complete separation of the desired and the stray light.