Vibrational spectroscopic, structural, linear and third-order nonlinear optical properties of isoniazid-vanillin hybrid

The isoniazid-vanillin hybrid (IVH), a Schiff base compound is synthesized and its vibrational spectral properties, structural, linear and third-order nonlinear optical (TNLO) characteristics are studied. IVH is examined by ¹H and ¹³C NMR, FT-IR and mass spectroscopic techniques. Solvent dependent TNLO properties are studied by Z-scan technique for which a 5 mW power CW diode laser with 650 nm wavelength is used. The order of nonlinear refractive index (n₂) and nonlinear absorption coefficient (β) is measured to be 10^-7 cm²/W and 10^-3 cm/W, respectively. The sample exhibits both positive and negative nonlinear absorption coefficient owing to the phenomenon of saturable and reverse saturable absorption, as well as negative nonlinear index of refraction as a result of self-defocusing. Self-defocusing is the result of thermal nonlinearity owing to the continuous absorption of light source. The real and imaginary component of the TNLO susceptibility of the sample is found to be the order of 10^-7 esu. The order of TNLO susceptibility (χ⁽³⁾) of IVH in polar solvents is measured to be 10^-7 esu. The effect of solvent spectral features on χ⁽³⁾ is also discussed. The results show that, the organic compound IVH is a promising candidate for applications in nonlinear optics. (author)