Rotational dependence of nonlinear parametric processes in diatomic molecules

Theoretical results on the rotational dependence of nonlinear parametric processes in diatomic molecules are generalized. Well-known results such as the parity of the nonvanishing nonlinear susceptibilities or the polarization effects are retrieved. Nonresonant susceptibility does not depend on the J rotational quantum number of the molecules involved in the process nor, consequently, on the temperature. It does depend on the J quantum numbers of both the ground and resonant state. The general rotational dependence of the resonant nth-order nonlinear susceptibility is derived in the general case of a single resonance. Three examples are given: ¹ Σ-¹Π three-photon resonant four-wave mixing, ¹Σ-¹Σ two-photon resonant four-wave mixing, and ²Π-²Σ two-photon resonant four-wave mixing. All the coefficients needed to compute the nonlinear susceptibility describing any four-wave mixing experiment are tabulated