Determination of absolute transition probabilities and particle densities by saturated fluorescence excitation

The high spectral intensity of pulsed dye lasers makes possible the saturation of atomic and molecular optical transitions. Because of the low‐intensity wings of the laser beam intensity distribution, the excited volume is only partially saturated. A mathematical procedure is described which yields a formal ’’saturated volume’’ which can experimentally be determined by measuring the degree of saturation using neutral optical filters in the path of the exciting laser beam. In this way, absolute transition probabilities and particle densities can independently be measured, and a mutual test on accuracy is possible. Preliminary results on CH and C2 produced in a low‐pressure C3H8/air flame are presented.