The propagation of coherent laser light in optical systems is simulated by the vectorial ray-based diffraction integral (VRBDI) method which utilizes vectorial diffraction theory, ray aiming, differential ray tracing and matrix optics. On a global scale the method is not restricted to the paraxial approximation, whereas it is properly used for a local representation of the wavefront close to an aimed detection location. First, the field of a monochromatic continuous wave on an input plane is decomposed into spherical or plane wave components. Then, these components are represented by aimed ray tubes and traced through an optical system. Finally, the contributions are added coherently on an output plane whose position has to be chosen according to ray-aiming requirements. Provided that the apertures in the optical system are large with respect to the wavelength the results are fairly accurate.