Absolute concentration measurements by pulsed laser-induced fluorescence in low-pressure gases: allowing for saturation effects

We present a simple method to account for the inevitable partial saturation of the excitation process in pulsed laser-induced fluorescence. The method allows the absolute concentration of a transitory species in a low-pressure gas to be determined by comparing the signal with that from a calibrating (stable) species of known concentration: the two species are excited with different laser powers, in the inverse ratio of their transition strenghts. The validity of the method is justified both theoretically and experimentally, and is applied to the measurement of CF radicals in a fluorocarbon discharge.