Quantitative nonlinear spectroscopy: A direct comparison of degenerate four-wave mixing with cavity ring-down spectroscopy applied to NaH

Cavity ring-down spectroscopy and degenerate four-wave mixing have been applied for spectroscopic studies, temperature determination, and measurement of relative dipole transition moments of photochemically produced sodium hydride, In our experiment, NaH was formed within a heat-pipe oven after 3p excitation of sodium in a hydrogen atmosphere with a second dye laser, The reaction product NaH was probed in the near ultraviolet part of the spectrum at 382 nm with 1-4-mu s delay to the excitation pulse using both a linear and nonlinear spectroscopic technique with a pulsed dye laser source (pulsewidth 15-ns full-width half-maximum) The strengths and limitations of these two spectroscopic techniques are discussed, Since the two processes depend on different parameters and the image-forming beams have different properties, it is difficult to define a single criterion for comparison, But our measurements indicate that cavity ring-down spectroscopy is a powerful tool with a sensitivity better than 10(9) particles per cm(3) and quantum state which is comparable to degenerate four-wave mixing in our case.