A calibrated two‐color temperature method has been developed for the measurement of time‐dependent temperatures in low‐pressure gases following laser excitation. Ratios of ir fluorescence signals arising from specific vibrational manifolds are used to determine the magnitude of laser heating, the vibrational temperatures of individual modes, and density fluctuations due to gasdynamic expansion following spatially inhomogeneous excitation. This technique has been applied to a prototype system consisting of SF6, SO2, and CH3F exposed to TEA CO2laser excitation of the &ngr;3mode of SF6. Prior toV‐T/Rrelaxation, this system cannot be described by a single vibrational temperature.