The application of the Laguerre-Gaussian (LG) and Hermite-Gaussian (HG) series expansions in the paraxial simulation of optical pulses is described and presented through examples of pulse modulation by diffractive Fresnel lenses and axicons. Using the FDTD technique we exhibit the physical propagation of a Hermite-Gaussian mode outside of the paraxial regime, with a width parameter of the same order of magnitude as the wavelength. In higher order modes this causes evanescence at the source of such modes, and we describe the loss of energy caused by this phenomenon. Using recently derived expressions for the non-paraxial propagation of Hermite-Gaussian modes, we discuss the use of modal techniques outside of the usual paraxial restriction, which allows for an efficient modal synthesis of Rayleigh-Sommerfeld diffraction effects in the far-field.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.