Large Third-Order Optical Nonlinearities of a Croconium Dye in Tetrahydrofuran Solution and in Poly(methyl methacrylate) Coating Films Measured Using Resonant Femtosecond Degenerate Four-Wave Mixing Technique

The third-order optical nonlinearities of a croconium dye in tetrahydrofuran (THF) solution and in poly(methyl methacrylate) (PMMA) coating films were measured using the femtosecond degenerate four-wave mixing (DFWM) technique under resonant conditions. The temporal profiles of the DFWM signal of the croconium dye were obtained with a time resolution of 0.3 ps (FWHM), and were found to consist of at least two components, i.e., the coherent instantaneous nonlinear response (electronic response) and the slow response due to the formation of excited molecules for both the THF solution and PMMA coating films. The electronic component of molecular hyperpolarizability, γe, of the croconium dye in the THF solution was determined to be ca. 4.6×10-29 esu at 817 nm. The electronic component of third-order nonlinear optical susceptibility, χ(3)e, of one of the present PMMA coating films containing the croconium dye was ca. 1.3×10-8 esu at 824 nm.