DENSMAT - FULLY TIME-RESOLVED SIMULATION OF 2-STEP PULSED-LASER EXCITATION OF ATOMS IN HIGHLY COLLISIONAL MEDIA

A program that simulates and displays the level populations of atomic systems exposed to dual-wavelength (i.e. two-colour) pulsed laser exci tation in highly collisional media (such as flames and plasmas) has be en developed. The program is based upon a previously published fully t ime-dependent density-matrix model that describes step-wise excitation s of atoms with degenerate states under collision-dominated conditions , and which thus goes beyond the rate-equations formalism. This model can predict such phenomena as Rabi flopping and a.c.-Stark splitting, shifting and broadening. The program can be used as a prediction tool for laser-enhanced ionization, laser-induced fluorescence, fluorescenc e dip spectroscopy and other two-colour laser-based spectroscopic expe riments. The program provides the user with a flexible four-level atom ic system, configurable as a one- or two-step excitation ladder, along with an ionization continuum and non-laser-connected level(s) that ma y act as trap(s) or metastable level(s). Parameters such as level dege neracy, collisional rates and laser pulse widths, shapes, wavelengths, intensities and bandwidths are accessible to the user. The program ca n display both the time development of the level populations and also level populations versus laser wavelength. This article is an electron ic publication in Spectrochimica Acta Electronica (SAE), the electroni c section of Spectrochimica Acta Part B (SAB). The hardcopy text is ac companied by a disk containing the program DensMat, an associated on-l ine help file and manual, an installation program, and data files pert aining to the examples illustrated in this article. The program runs u nder Windows 3.1 on an IBM-compatible computer.