Abstract

The third order nonlinear susceptibilities ${\chi }_{\text{xxxx}}^{(3)}\left(-{\omega }_3;{\omega }_1,{\omega }_1,{\omega }_1\right)$ of the dyes rhodamine 6G, fuchsin and methylene blue in methanol are determined versus concentration by non-phasematched third harmonic generation with picosecond light pulses from a mode-locked Nd-glass laser. For quantitative measurements a special experimental arrangement is used that avoids disturbing light production by surrounding media. The contributions from air are suppressed by slightly focusing the light beam to a sample cell in a vacuum chamber. The cell windows are adjusted to an even integer of the coherence length ℓ_coh=π/Δk (Δk=k₃-3k₁=3ω₁ (n₃-n₁)/c is the wave vector mismatch) so that the third harmonic signal at the exit surface is equal to the third harmonic signal at the entrance surface. The output third harmonic signal originates only from the sample under investigation. By laterally displacing the slightly wedged cell the Maker fringe pattern of light generation is detected for transparent media.

© 1984 Optical Society of America