Study on nonlinear optical properties of two novel dmit2− salts by Z-scan technique

Two novel dmit2− salts: [C16H33(CH3)3N]Co(dmit)2 and [C16H33(CH3)3N]Ni(dmit)2 (abbreviated as CTCo and CTNi, respectively, and dmit2− = 4,5-dithiolate-1,3-dithiole-2-thione), are synthesized and their third-order optical nonlinearities of the acetone solutions are investigated using Z-scan technique with 40 ps pulse width at 1064 nm. The Z-scan spectra reveal both CTCo and CTNi sample solutions possess large negative nonlinear refraction, exhibiting a self-defocusing effect. In addition, slight two-photo absorption and strong saturable absorption have been found in CTCo and CTNi, respectively. The molecular second-order hyperpolarizability γeff of the CTNi molecule was estimated to be as high as (−4.6 ± 0.2) × 10−30 esu, which was four times larger than that of CTCo. An explanation for this enhancement is given. All the results suggest that these materials may have potential applications in the field of nonlinear optics.