Nonlinear Optics

A nonlinear image technique for characterization of the optical nonlinearities is used to investigate the solid semiconductor ZnSe at 600 nm. The method based on a 4f nonlinear image technique with a phase object is used to obtain the diffraction pattern of the nonlinear filter in solid ZnSe located at the Fourier plane by a CCD camera. The nonlinear absorption coefficient and nonlinear refraction index were both obtained by fitting the nonlinear image. Good agreement between the experiment data and the simulated result are obtained indicating a sensitive and powerful method for nonlinear optical measurements.

Bisthiourea Zinc Acetate (BTZA) a semi organic material has been synthesized by slow evaporation method using water as a solvent. The solubility studies have been carried out in aqueous solution in the temperature range 25 ˚C – 45 ˚C. Crystals have been grown from low temperature solution method by slow evaporation of saturated aqueous solution at room temperature. Single Crystal X-ray diffraction study has been carried out to determine the lattice parameter of the grown crystal. The spectral bands have been compared with similar thiourea complexes using FTIR spectrum in the range 400 – 4000 cm-1. Optical transmittance and absorption percentage of the grown crystal have been measured from UV-Vis studies. The thermal behavior has been investigated by thermogravimetric (TGA) and Differential Thermogram analyses (DTA). The mechanical strength and work hardening coefficient of the grown crystal have been analyzed by Vicker’s microhardness method. Keywords: Growth from solutions; X-ray d...

We have investigated the nonlinear optical interaction of uniform and kink states of a nematic and a ferrofluid-doped nematic (ferronematic) liquid crystal with an incident laser field. We find that the transition between the permitted uniform oreintational states of these systems is of first order in the case of nematics, and of second order in the case of ferronematics. In the latter case we also find the phenomenon of reentrance. We find new kink states in a magnetic field with topological winding different from π in the case of nematics, and 2π in the case of ferronematics. In ferronematics, due to grain segregation the phase diagrams for uniform and kink states are entirely different. In these systems we find a first or second order structural transformation from a single kink into a pair of kinks. Further, we obtain a rich variety of kink states as the intensity of the laser field is varied.

The nonstationary parametric interaction of waves in negative-index metamaterials is studied in the second-order dispersion theory. A nonlinear interaction between a long pulse of a strong pump wave and an ultrashort pulse with quadratic phase modulation is considered. The results of calculating the shape of the spectrum of an excited signal wave are presented. A comparison is made with the case of interaction in an ordinary medium. It is shown that the effects of group-velocity dispersion and dispersive spreading in such materials lead to a narrowing of the spectrum of the excited wave. The presence of phase modulation of the exciting idler pulse promotes broadening of the central maximum of the spectrum of the excited signal wave. As the modulation factor increases, the fragmentation of the excited pulse is observed.