Self-focusing in SF6

We calculate the susceptibility responsible for self-focusing in SF(6) in two parts, the v(3)-ladder contribution and the quasi-continuum contribution. Our v(3)-ladder vibrational model is a classical triply degenerate anharmonic oscillator in the Cartesian basis with the anharmonicity parameters chosen to be consistent with the latest spectroscopic analysis of the 3v(3)-overtone spectrum. The rotational structure is represented by a distribution of these oscillators in which the distribution is chosen to correspond to the spectrum of the v(3) fundamental. Using our previously published model, we find that the quasi-continuum contribution is much smaller than the v(3)-ladder contribution to the susceptibility and always decreases with increasing laser energy. We find that the v(3) ladder is entirely responsible for self-focusing in SF(6) . The susceptibility curves show qualitative agreement with the 300-K self-focusing data of Nowak and Ham [Opt. Lett. 6, 185 (1981)] at CO(2)P(28), P(20), and P(10) in SF(6). Calculations with a two-dimensional diffraction-propagation code show good quantitative agreement with the Nowak and Ham data at CO(2)P(20) and P(10).