The Effect of the Dye Concentration on the Nonlinear Properties of the Laser Dye DQOCI Doped with PMMA Films by Using Z-Scan Technique

Abstract

In this study the effect of the laser dye DQOCI concentration doped films on the nonlinear properties was studded by using z-scan technique which showed an interesting nonlinear optical characteristic. The dye DQOCI was dissolved in ethanol with different concentration and doped with the polymer PMMA by a spin coating method. Z-scan experiment was performed using Nd: YAG pulsed laser at532 nm, in two parts. The first part was done using a closed-aperture placed in front of the detector to measure the nonlinear refractive index. In the second part; the aperture in front the detector was removed (open aperture) to measure the nonlinear absorption coefficient. The experimental results for closed aperture show that the dye doped films exhibits negative refractive index (self-defocusing) for all concentrations. The results show also that the nonlinear refractive index and the third order nonlinear susceptibility increased with the increasing concentration. The observed nonlinearity curves of the doped films by using open aperture z-scan exhibited third order nonlinearity as it fit to saturation absorption. Most of the molecules occupy the excited state, and the ground state is bleached, the system becomes increasingly transparent to the incident laser puls at 532 nm resulting in a saturation of absorption .The third order absorption coefficientβ and the imaginary part of susceptibility I’m χ^(3). Values were increased as the concentration of the dye was increased .This is due to increasing of the number of dye molecules which thermally excited resulting in an enhanced effect. DQOCI doped films with different concentrations have a good optical limiting response. The limiting threshold and the limiting output power were reduced as the concentration was increased which make these films a good candidate for optical limiting applications.