Third-harmonic generation in positively dispersive gases with a novel cell

This paper presents an experimental study of the third-harmonic generation in positively dispersed Ar and tightly focusing a dye laser beam within the cell containing the gas. Destructive interference is eliminated by providing along the beam axis a suitable density gradient of the nonlinear gas, thereby restricting to a focal half-space the conversion of the frequency. Results are compared to theoretical calculations and show the applicability of the technique for direct and accurate measurements of third-order susceptibility of gases.