Perturbative Nearly-Degenerate Four-Wave Mixing Lineshapes in Gases

Nearly-degenerate four-wave mixing (NDFWM) spectroscopy1 and the closely related tunable-laser-induced grating spectroscopies2 have proved to be valuable tools in the study of nonlinear optical interactions. The NDFWM spectral lineshape provides information concerning the lifetimes,3 and therefore the identities, of multiphoton scattering mechanisms. In addition to the great number of investigations in liquids and solids, considerable research has focused on wave-mixing in resonant atomic gases for phase conjugation applications.4 Although many special cases have been discussed, general expressions that include the effects of molecular motion for the NDFWM lineshape in gases have not been previously reported. The present study is motivated by an interest in understanding the mechanisms contributing to degenerate four-wave mixing (DFWM) spectroscopy in molecular gases for application to combustion and chemical physics research.