Study of Solvent Dependent on Third-Order Nonlinear Optical and Thermo-Optic Coefficient of Malachite Green Dye.

This study reveals the solvent dependent third-order nonlinear optical (NLO) features of malachite green (MG) dye using Z-scan technique. MG dye is dissolved in polar solvents, including DMF, DMSO, ethanol, acetone, methanol, and 1-propanol. The study employs the Z-scan instrument, using a continuous wave (CW) laser as the excitation source, operating at a wavelength of 650 nm. The closed aperture (CA) and open aperture (OA) Z-scan techniques are used to assess the nonlinear indices of refraction (n) and nonlinear coefficient of absorption (β) of MG dye. MG dye demonstrates both saturable absorption (SA) and reverse saturable absorption (RSA) in the OA Z-scan results, due to negative and positive NLO absorption coefficients. MG dye proves a self-defocusing NLO refractive index while operating under low-power conditions. The third-order NLO susceptibility (χ) of MG dye in various liquids are calculated to be the order of 10 esu. Multilinear regression fit is applied here to investigate the various intermolecular interactions between the solute and solvent. MG dye exhibited large thermo-optic coefficient of the order of 10 K is observed. The results give important new information about the characteristics of MG dye and indicate potential sources of material for NLO applications in future.