Third-order nonlinearity measurements of PbPc(CP)₄/DMF

The third-order nonlinear absorption and refraction of PbPc(CP) ₄/DMF solution between the wavelengths of 500 and 600 nm are studied using the modified double 4 f imaging system. The experimental results show an obvious wavelength dependence of the third-order nonlinear absorption and refraction coefficients. Particularly, the nonlinear dynamics of PbPc(CP) ₄/DMF solution at 532 nm are studied using a time-resolved pump-probe system based on a 4 f nonlinear imaging technique with phase object. Experimental results under picosecond (ps) pulses clearly show that the nonlinear dynamics of PbPc(CP)₄/DMF originate from excited-state absorption and refraction. A three-level model is used to interpret the observed reverse saturable absorption and self-focusing effect. Large absorption and refraction cross sections for the first singlet excited state with a fairly long lifetime are determined. Z-scan experiments under nanosecond and picosecond pulses are performed to verify the experimental results. The nonlinear properties of neat N,N-dimethylformamide (DMF) and its contribution to the nonlinear refraction of the solution are also determined.