A method is developed for extending conventional ray-tracing techniques to include diffractive effects associated with focused laser beams. The main idea is to provide rays with a distribution of directions at each point in space, as in radiative transfer calculations. The Wigner phase-space distribution function is used to obtain formulas for the spread of ray angles that yield the correct diffraction patterns for coherent and partially coherent beams. This method is readily implemented numerically by means of computer programs that are used in Monte Carlo radiative transfer calculations.
© 1976 Optical Society of America
Frederick Tappert, "Diffractive ray tracing of laser beams," J. Opt. Soc. Am. 66, 1368-1373 (1976)