The Nonlinear Optical Studies of Poly Ortho-Toluidine with CW Visible Laser Beam
摘要
The nonlinear optical properties of poly ortho-toluidine (POT) under irradiation with a laser beam of wavelength of 473 nm having a Gaussian intensity profile have been investigated. The resulting diffraction ring patterns (DRPs) have been studied against the laser beam power input and laser beam wavefront type. The temporal evolution of the DRPs has also been studied. The study of Z-scans prove that the POT have a negative nonlinear refractive index (NLRI) due to the closed Z-scan and the POT having no nonlinear absorption coefficient since the open Z-scan resulted in a horizontal line relationship of the transmittance against the sample position. The DRPs evolve from a single spot, with a small area, then breaks to DRPs symmetric in the x–y plane with respect to the z-propagation direction. then loses its symmetry so that they appear compressed in the vertical direction due to the vertical convection thermal current that overcomes the horizontal conduction thermal current. The POT NLRI has been calculated based on the DRPs and Z-scan and is equal to 3.99 × 10−7 cm2/W and 0.19 × 10−7 cm2/W. respectively. The difference between the two values is due to the high-power input used in the first technique. The DRPs were numerically simulated using the Fresnel—Kirchhoff diffraction integral resulting in reasonable agreement between the experimental and calculated results. The optical limiting property proved to occur in the POT with the limiting threshold value of 15.5 mW using the same wavelength.