Linear and nonlinear optical properties of an organic polymer composite film

An organic material, 4,5-bis(benzoylthio)-1,3-dithiole-2-thione (BBDT), was synthesized. The thin film of BBDT doped into poly(methyl methacrylate) (PMMA) was prepared using spin-coating method. Its linear optical properties were characterized with prism coupler (SPA-4000, Korea). The third-order nonlinear optical (NLO) properties were investigated using Z-scan technique with pulses of picoseconds at 532 nm. The Z-scan spectra reveal a strong nonlinear absorption (reverse saturable absorption) and a positive nonlinear refraction. The nonlinear absorption coefficient is calculated to be 1.302×10⁻⁹m/W. The nonlinear refractive index is 2.243×10⁻⁹esu. The results show that the film exhibits a great nonlinear optical response.