Kinoform apodization by using of programmable diffractive optical elements

Abstract

The apodization of diffractive optical elements can be realized by a local change of their diffraction efficiency. In the case of lithographic elements with step -like structure of the p eriod, the variable diffraction efficiency can be achieved by a gradual transformation of the 2 m step kinoform into its conjugate counterpart across the apodization region. In the present contribution we show experimental results confirming this idea, which until no was verified only by simulations. The apodized quaternary grating with locally varying diffraction efficiency was obtained on a SLM device as a programmable diffractive optical element by changing gradually the period's profile.Knowledge of the phase heights of the SLM's pixels is required for successful implementation of the apodization function. It was determined from Fresnel images of the binary phase gratings with different phase step height programmed on the SLM. The Fresnel images become then binary and their visibility depends on the phase height of the grating in a known way, what makes possible to calibrate the SLM.