2-COLOR RESONANT 4-WAVE-MIXING - ANALYTICAL EXPRESSIONS FOR SIGNAL INTENSITY

We present analytical signal expressions for each two-color resonant f our-wave mixing (TC-RFWM) scheme that can be used for double-resonance molecular spectroscopy in the limit of weak fields (no saturation). T he theoretical approach employs time-independent, diagrammatic perturb ation theory and a spherical tensor analysis in an extension of recent treatments of degenerate four-wave mixing [S. Williams, R. N. Zare, a nd L. A. Rahn, J. Chem. Phys. 101, 1072(1994)] and TC-RFWM for the spe cific case of stimulated emission pumping [S. Williams et al., J. Chem . Phys. 102, 8342 (1995)]. Under the assumption that the relaxation of the population, the orientation, and the alignment are the same, simp le analytic expressions are derived for commonly used experimental con figurations. The TC-RFWM signal is found to be a product of a concentr ation term, a one-photon molecular term, a line shape function, and a laboratory-frame geometric factor. These expressions are intended to f acilitate the practical analysis of TC-RFWM spectra by clarifying, for example, the dependence on beam polarizations and rotational branch c ombinations. (C) 1997 American institute of Physics.