Third-order nonlinear optical properties of a dmit2− salt by Z-scan technique

Abstract

The non-resonant and resonant third-order nonlinear optical response of a charge-transfer salt (NBu4)2 [Zn(dmit)2] (dmit=2-thioxo-1,3-dithiole-4,5-dithiolate) are investigated using the Z-scan technique with 38 ps laser pulse duration at the fundamental wavelength 1064 nm and half-wavelength 532 nm. Under 532 nm excitation, the solution exhibits strong saturable absorption (SA) with a nonlinear absorption coefficient β =−2.94 cm GW−1 and a negative third-order nonlinear refractive index attributed to self-defocusing, which is contrary to that under 1064 nm excitation. For the resonance factor, calculated as 32.2, the third-order nonlinear refractive index under the same experimental conditions is enhanced 102 times as compared to that under 1064 nm excitation. The molecular second hyperpolarizabilities (esu) and (esu) are obtained from the experimental calculated results.