Experimental investigations on nonlinear absorption and refraction of LN/PMMA nanocomposites as a function of electric field

Lithium niobate (LiNbO₃; LN), is an important photonics material. In this article, nonlinear absorption and nonlinear refraction properties of poly(methyl methacrylate) (PMMA), 0.10 wt% LN/PMMA nanocomposites have been investigated through Z-scan technique using a continuous wave laser (632.8 nm wavelength) of Gaussian intensity profile. For preparing the nanocomposites, nearly stoichiometric LN nanoparticles were used. Since LN is a polar material, Z-scan experiments were performed on 0.10 wt% LN/PMMA nanocomposites prepared under different strengths of electric field to study the influence of the electric field on the above nonlinear optical properties of the prepared samples. On dispersing LN nanoparticles into the PMMA matrix, switching from reverse saturable to saturable absorption, and self-defocusing to self-focusing nonlinearity was observed. It was found that the value of nonlinear parameters, namely saturable intensity (I_S) and nonlinear refractive index (n₂) of LN/PMMA nanocomposites can be tailored with the help of an external electric field during nanocomposite preparation. In the case of n₂, an inversion of the sign was also found beyond the threshold strength of the electric field.