Nonlinear optical studies of newly synthesized polythiophenes containing pyridine and 1,3,4-oxadiazole units

We report measurements of the third-order nonlinear optical properties of a newly synthesized thiophene- based copolymer. The nonlinear transmission measurements were performed on the copolymer dissolved in tetrahydrofuran by employing the single beam Z-scan technique. Q-switched laser output at 532-nm wavelength was used for this purpose. The nonlinear absorption coefficient, β, nonlinear refractive index, n₂, and the real and imaginary parts of third-order susceptibility, x⁽³⁾, were, 18.93 cm/GW, 3.037 x 10 ^-17 m²/W (1.022 x 10^-10 esu), 1.512 x 10^-20 m²/V²(-1.080 x 10 ^-12 esu) and 0.399 x 10^{-20 2}m/V² (0.285 x 10 ^-12 esu), respectively. The excited state absorption crosssection σ_exc, was found to be larger than the ground state absorption crosssection σg, indicating reverse saturable absorption (RSA) in the copolymer sample. The co- polymer exhibits an optical power limiting threshold of about 120 μJ and saturated output of less than 80 μJ. Hence, the copolymer seems to be a promising material for photonic device applications.