The diagnostic potential of polarization spectroscopy (PS) technique using short-pulse (100 ps) lasers for quantitative measurements of species concentration in reacting flows is investigated. The use of a short pulse laser significantly decreases the collision-rate dependence of the PS signal in the nanosecond-laser pulse-length regime. The investigation is carried out by direct numerical integration (DNI) of a multistate formulation of the density matrix equations at numerous grid points along the phase-matching axis and by summing the polarization contribution from each of these grid points for the counter-propagating pump/probe geometry. The effects of Doppler broadening are included by solving the density matrix equations for numerous velocity groups. At high pump intensities, the dependence of the PS signal on collision rate decreases drastically. We also have begun investigating the effects of hyperfine structure on the PS signal.
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