M.H. Majles Ara

Characterisation and nonlinear optical properties of CdS nano-particles

CdS nano-particles have been synthesised using chemical precipitation. The formation and microstructure of CdS nano-particles were monitored by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectrum and z-scan technique. Using the UV-Visible, the band gap of this nano-particle is obtained about 3.54 eV and the spectrum of this material shows a 310 nm peak. X-ray diffraction pattern (XRD) shows that the obtained CdS nanostructures are of hexagonal phase and indicates that the average crystallite size is 1.2 nm. Average particle size obtained from SEM analysis about 4.35 nm and agree with XRD result. Optical limiting property of CdS nano-particles is studied, the linear absorption coefficient was obtained about 0.044 cm−1. Furthermore the nonlinear refractive index, n2, and nonlinear absorption coefficient, β, were measured using close and open aperture z-scan respectively using a CW He-Ne laser at 632.8 nm. As nano-particles have strong absorption coefficient to obtain purely effective n2 we divided the closed aperture transmittance by the corresponding open aperture in the same incident beam intensity. The nonlinear refraction index of this nano-particle was measured in order of 10−7 (cm²/W) with positive sign and the nonlinear absorption coefficient was obtained in order of 10−3 (cm/W)) with negative sign.

Synthesis of composite Au/TiO2 nanoparticles through pulsed laser ablation and study of their optical properties

This paper is a report on the synthesis of composite Au/TiO2 nanoparticles (NPs) using a novel and chemically clean method by ablating a gold target immersed in colloidal TiO2 NPs using 1064 nm Nd:YAG laser pulses. Further, the NPs were characterized through ultraviolet?visible spectroscopy, transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. In addition, the nonlinear optical response of the synthesized samples was studied under continuous wave He?Ne laser irradiation.

Electro-optical Kerr effect of azo-dye-doped liquid crystals using nulled intensity method

ABSTRACT The electro-optical Kerr effect and pre-transition behavior have been investigated for different concentration of dimethyl-aminoazobenzene dye-doped nematic liquid crystal by using the nulled intensity method. Measurement results have showed that the molecular reorientation of liquid crystals induced by photoisomerization of azo dyes come about to increase an amount of Kerr constant at low percentages of dye concentration. Additionally, the results of pre-transition temperature which were obtained by extrapolating the invers Kerr constant as a function of temperature have been found to be in good agreement with predictions of the Landau-De Gennes model.

Dielectric properties of nematic liquid crystal doped with Fe3O4 nanoparticles

ABSTRACT The influence of Fe3O4 nanoparticles (NPs) on dielectric properties of planar and homeotropic oriented nematic liquid crystals (NLCs) were studied during the temperature interval of 298–322 °K. It was found that the dielectric permittivity was considerably increased by adding NPs mass percentages. The structural characterization of the synthesized NPs with the scale 14–18 nm has been analyzed by the X-ray diffraction and field-emission scanning electron microscopy results. The obtained dielectric anisotropy () and mean dielectric () have shown an immense increment in the value of 1% and 10% wt. NPs doped NLCs, respectively. These results were assigned to the strong dipole–dipole interaction between the superparamagnetic particles and the surrounding liquid crystal molecules.

Early diagnosis by comparison between interferometry and Z-scan methods to measure NLO refraction of human skin cancer (BCC and SCC) in vitro

As the nonlinear refractive index (n2) of human cancerous skin tissues is an important parameter in characterizing the optical response in laser–tissue interaction, the interferometry method was applied for early diagnosis. Simple method of interferometry measurement has been applied to measure the tissues’ n2 in vitro from cancerous human skin samples (BCC and SCCs) in three thicknesses. Also, to compare the sensitivity and accuracy of the interferometry method, the Z-scan method was used. The results show that in comparison with healthy skin tissue, the cancerous skin has nonlinear response and this index increases with the thickness of samples.

Temporal dynamics of optical bistability and modulation instability in colloidal nanoparticles

Abstract. Colloidal nanoparticles are attractive optical materials for their low threshold nonlinear response and thus all-optical, nondestructive features which are important in biomedical optics and optical processing. We develop a theoretical scheme based on numerical solution of Nonlinear Schrödinger Equation and nonideal gas model of nonlinearity to investigate temporal analysis of optical bistability (OB) and modulation instability in colloidal nanoparticles. Our scheme determines the dependence of a nanosuspension system dynamic state on characteristic/control parameters including external feedback depth, nanosuspension length, and the initial density of nanoparticles as well as the optical input power. We show that these parameters are intensely correlated. We also indicate that the nonlinear response of nanosuspension may be saturated over a threshold of input power, and thus an unexpected procedure of system evolution toward stability rather than transition to chaos will occur. Consequently, provided that internal feedback is present inside the nanosuspension controlling chaos will be attainable by simply adjusting the optical input power as the control parameter in contrast to the other chaos control methods which require external injection. Finally, we propose an approach which gives a measure of switching time to optimize OB. The optimum results are obtained for the lowest taken values of characteristic/control parameters.

Investigation of the Effect of Capping Agent Molecule Type on the Nonlinear Optical Responses of CdS Nanocrystals

In this work CdS nanocrystals (NCs) have been synthesized with thermochemical method using two different capping agent molecules: thioglycolic acid (TGA) and thioglycerol (TG). XRD analysis demonstrated hexagonal crystal phase for both samples. Band gap of NCs was obtained 3.13 eV and 3.2 eV for TG capped and TGA capped NCs respectively. The nonlinear refractive index and nonlinear absorption coefficient were obtained in order of 10−8 (cm2/W) and 10−3 (cm/W) for both samples, respectively. The linear absorption coefficient was obtained about 2.63 cm−1 and 1.14 cm−1 for TG capped and TGA capped NCs, respectively.

Thermal nonlinear optical properties of TiO2 nanocrystals prepared through pulsed laser ablation

Titanium dioxide (TiO2) nanoparticles (NPs) were synthesized using the pulsed laser ablation method by irradiating a titanium target immersed in distilled water with 1064 nm, Nd:YAG (yttrium aluminum garnet) laser pulses. The indirect band gap of the NPs was estimated with the aid of ultraviolet/visible spectroscopy. Transmission electron microscopy showed the NPs to be spherical in shape and to vary from 5 to 50 nm. The average size of the NPs and their crystalline phases were determined by means of x-ray diffraction analysis. The thermal conductivity of the nano-TiO2 colloids was measured at a temperature of 25 °C. The single-beam z-scan technique was employed to obtain the nonlinear index of refraction (n2) and the nonlinear absorption coefficient (β) under continuous wave He–Ne laser excitation at different input powers. Thermo-optical coefficients of the NPs were calculated using the z-scan results.

Intrinsic optical bistability in doped polymer

Abstract One of the most interesting and applicable effects of nonlinear optics is optical bistability. This phenomenon is exhibited by certain resonant optical structures where it is possible to have two stable steady transmission states for the device, depending on the history of the input. Such a bistable device may be useful for optical computing elements as a result of its memory characteristics. Optical bistability behaviour is usually observed by inserting a nonlinear matter inside a Fabry–Perot interferometer. But in this study, it was shown that this can be achieved without the application of any optical resonator. Two laser beams were used to interact with the photorefractive media (doped PMMA polymer) which resulted in the bistability of the intensity of transmitted wave. Feedback was provided by a periodic grating created in the photorefractive polymer PMMA.