LINE NARROWING IN MULTIRESONANT 3RD ORDER MOLECULAR SPECTROSCOPIES

A complete analysis of line narrowing in third order, steady-state spectroscopies is given in terms of a recently developed perturbative theory for the nonlinear susceptibility. This approach rigorously includes realistic population dynamics and feeding without significantly complicating the analytic solutions. Unrelaxed resonant emission (i.e., resonant fluorescence and Raman emission) and coherent anti-Stokes Raman scattering (CARS) are treated as examples. Inhomogeneous broadening is included by an analytic contour integration over an inhomogeneous strain distribution. Unlike most existing approaches to line narrowing, both coherent and incoherent spectroscopies are treated by this same formalism, allowing the capabilities of each to be compared. A novel pictorial representation wich facilitates rationalization of line narrowing and its absence in certain coherent spectroscopies is introduced. Feeding effects are shown to alter line-narrowing behavior in third order for incoherent resonant emission but only in fifth order for CARS. © 1990.