Imaging and dispersion analysis of a diffractive optical element for infrared sensors

Diffractive optical elements (DOEs) like diffractive lenses are used in infrared sensors to combine spectral filtering and focusing in a single optical element. Spectral resolution, dispersion, and imaging properties depend on the geometry of the setup. These dependencies are analysed by ray tracing for different arrangements, using the local grating period of the DOE. An optimized setup for infrared gas measurements is presented that does not rely on filters, consisting only of an emitter, a detector and the DOE. Additionally the system's point spread function is taken into account. It is calculated by an efficient implementation of the Rayleigh–Sommerfeld wavefield propagation technique. A prototype, based on a two-level DOE, is presented and measurements confirm the simulation results.