Vibrational hyperpolarizability of SF6

Expressions are derived for the vibrational second hyperpolarizability γv of SF6, in the static limit and for the nonlinear‐optical processes of the dc Kerr effect, electric‐field‐induced second harmonic generation (ESHG), and third harmonic generation (THG). These expressions give γv in terms of vibrational transition dipole, polarizability, and first hyperpolarizability matrix elements (μ,α,β). The matrix elements needed in the numerical evaluation of γv are obtained from the literature and from the Raman scattering measurements reported here. In the static limit it is found that γv≈20 γe, where γe is the electronic contribution to γ. At optical frequencies γv is still comparable to γe in magnitude, and it shows significant frequency dependence.