Nonlinear optical and DFT study of natural dye extracted from Lawsonia inermis leaves using He–Ne laser

This study presents the third-order nonlinear optical (NLO) properties of a natural dye derived from lawsonia Inermis, investigated using Z-scan with continuous-wave He-Ne laser at a wavelength of 632.8 nm. The natural dye exhibited self-defocusing nonlinear refractive index and reverse saturable absorption (RSA) based nonlinear absorption coefficient. The self-defocusing behavior arises from thermal nonlinearity, while the RSA effect is attributed to a higher excited-state absorption cross-section compared to the ground state. The nonlinear refractive index and nonlinear absorption coefficient of the natural dye are determined to be on the order of 10^-8 cm²/W and 10^-3 cm/W, respectively. The natural dye exhibited a substantial third-order NLO susceptibility (χ³), measured to be on the order of 10⁻⁷ esu. FT-IR analysis is employed to determine the functional groups present in the natural dye. Density functional theory (DFT) calculations corroborate the experimental findings by providing insights into the NLO properties, molecular electrostatic potential (MEP) and frontier molecular orbit (FMO) of the natural pigments. The results offer valuable insights into the natural dye extracted from lawsonia Inermis leaves, highlighting its potential for nonlinear optical applications.