  The goal of this effort is to establish the conditions and limits under which
the Huygens-Fresnel principle accurately describes diffraction in the Monte
Carlo ray-trace environment. This goal is achieved by systematic
intercomparison of dedicated experimental, theoretical, and numerical results.
We evaluate the success of the Huygens-Fresnel principle by predicting and
carefully measuring the diffraction fringes produced by both single slit and
circular apertures. We then compare the results from the analytical and
numerical approaches with each other and with dedicated experimental results.
We conclude that use of the MCRT method to accurately describe diffraction
requires that careful attention be paid to the interplay among the number of
aperture points, the number of rays traced per aperture point, and the number
of bins on the screen. This conclusion is supported by standard statistical
analysis, including the adjusted coefficient of determination, the
root-mean-square deviation, and the reduced chi-square statistics.
