2-PHOTON-RESONANT 4-WAVE-MIXING SPECTROSCOPY OF ATOMIC-HYDROGEN IN FLAMES

We report a new diagnostic technique based on resonant four-wave-mixin g spectroscopy of the two-photon 1s-->2s transition in atomic hydrogen . Observations including Doppler-free spectral lineshapes and saturati on behavior are related to models for the nonlinear optical processes. Two-photon wave-mixing measurements of atomic hydrogen concentration in laboratory flames at pressures of 30-760 Torr appear to be less sus ceptible to errors from collisional quenching than similar measurement s made using laser-induced fluorescence.