Resonant nonlinear refraction of 4.3-μm light in CO2 gas

Abstract

We use time- and frequency-resolved measurements of self-focusing and self-defocusing of 4.3-\ensuremath{\mu}m radiation in ${\mathrm{CO}}_{2}$ gas to study the resonant nonlinear optical response in the vicinity of individual rovibrational lines. Measurements over a range of lines on the $4P$ and $4R$ branch of the 000-001 transition indicate that the nonlinear response of ${\mathrm{CO}}_{2}$ is strongly affected by power broadening, resulting in a sign reversal of the nonlinearity as compared to that of a saturable two-level system.