Angular spectrum method

Summary

The angular spectrum method computes how a monochromatic wave field propagates from one plane to a parallel plane. It writes the field in the first plane as a superposition of plane waves by a two-dimensional Fourier transform. Then it moves each plane wave by multiplying it by a phase factor, and transforms back. Components with high spatial frequency become evanescent waves that decay away from the plane. The method is exact for the Helmholtz equation in a homogeneous medium and is equivalent to the Rayleigh–Sommerfeld formula.