Zemax Development Corp.'s optical system design program supports the definition of high-order and multimode laser beams in its physical optics propagation mode. A tool for modeling laser beams, the program uses diffraction calculations to propagate a wavefront through the optical system surface-by-surface without using rays. It can calculate and optimize beam characteristics, such as the M2 quality factor, and beam centroid and effective width. It can display beam irradiance or phase in correct dimensions and units at any surface in the optical system, in surface, contour, gray-scale, false-color or cross-section plots. The program enables realistic, imperfect laser beams to be propagated through any optical surface to account for diffraction, aberrations, tilts and apertures, and the beams can be stored as data files for later use.