Comparison of electromagnetic and scalar methods for evaluation of diffractive lenses

Abstract

We compare scalar and electromagnetic methods for computing fields in the focal regions of diffractive lenses (DLs). The DL is treated locally as a linear grating with slowly varying period and groove orientation. Both the standard complex-amplitude transmission method and rigorous electromagnetic diffraction theory are employed to obtain the field immediately behind the DL. The field in the focal region is then evaluated using the first Rayleigh-Sommerfeld diffraction formula. It is shown that local optimization of the diffraction efficiency by modification of the grating profile improves the intensity at the focal point significantly for DLs faster than f:2. Improvements of 18% and 41% are obtained for four-level f:1 and f:0.5 lenses of focal length 1 mm at λ = 633 nm.