  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.
