Low-power Z-scan study of nonlinear refractive index and absorption coefficient of acid blue 129 dye-doped polymer thin film

This article reports the nonlinear refractive index (n₂) and nonlinear absorption coefficient (β) of acid blue 129 (AB 129) dye-doped polyvinyl alcohol (PVA) thin film with different dye concentrations using Z-scan technique. The experimental technique consists of a continuous wave laser with 5 mW power working at 635 nm wavelength. The normalized transmittance curve suggests that the dye-doped polymer film exhibits a self-defocusing nonlinear index of refraction and a large nonlinear absorption coefficient ascribed to the behaviour of reverse saturable absorption. The order of third-order NLO susceptibility of the sample is estimated to be 10^‒5 esu. The dye-doped polymer films show a low-limiting threshold of 0.15 kW cm^–2 at 0.04 mM dye concentration and believed that the prepared thin film is a suitable candidate for application in optical limiting. The self-diffraction pattern is observed at far-field and estimated the nonlinear refractive index of the thin film using this technique. The results of the nonlinear refractive index of the sample obtained from the self-diffraction method are comparable with Z-scan results.