Large Third-Order Optical Nonlinearity and Fast Response of a Squarylium Dye

The third-order optical nonlinearities and responses of a squarylium dye, 2,4-di-3-guaiazulenyl-1,3-dihydroxycyclo\-butenediylium dihydroxide, in tetrahydrofuran (THF) solution and in polystyrene (PS) coating films are measured by the femtosecond degenerate four-wave mixing technique under resonant conditions. The molecular hyperpolarizability g of the squarylium dye in the THF solution is determined to be 3.0 × 10^-29,esu at 764nm, and its electronic component γ_e is determined to be 1.1 × 10^-29esu. The third-order nonlinear susceptibility x⁽³⁾ of one of the present PS coating films containing the squarylium dye is as high as 3.1 × 10^-8esu at 800nm, and its electronic component x⁽³⁾_-e is 1.3 × 10^-8esu.