Numerical calculation of near field scalar diffraction using angular spectrum of plane waves theory and FFT

t is a known fact that near field diffraction or Fresnel diffraction calculations are difficult to perform exactly. It is in general necessary to make some approximations in order to obtain a more suitable form. In this work, a numerical implementation based on angular spectrum theory for near field diffraction is presented. The method uses Fast Fourier Transforms (FFT) and it turns out to be accurate and fast. In order to show the capabilities of the method, diffraction near field for a circular aperture and a spiral slit are studied. Numerical and experimental results are shown. This method could be useful to implement pc based physical optics learning.