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In this paper, for the first time, we introduce a simple way for finding the nonlinear optical properties of nanoparticles. The Michelson interferometer was used for calculating nonlinear refractive index. In comparison with conventional methods, the interferometry has high sensitivity and uses a single coherent beam that reduces the complexity and cost of experimental setup. The He-Ne laser with 75 mW laser irradiation at 632.8 nm was applied to different concentrations of TiO2 nanoparticles as a notable sample. By analysing the changes at interferometric patterns of different samples, the magnitude of (n2) was obtained in 10-8 cm²/W order. To confirm the interferometry results, the common Z-scan method was used to measure the nonlinear refractive index which reveals that the results are in good agreement with the interferometry method. [ABSTRACT FROM AUTHOR]

The optical properties of benign and malignant human brain tumors were investigated to provide a new diagnosis method. We studied various samples of adult human brain tissue (male and female) in two linear (by Optical density) and nonlinear (by Z-scan method) regimes. The obtained experimental results show that optical density for malignant is more than benign tissues and the nonlinear behavior of benign and malignant tissues are completely different because the nonlinear refractive index had a negative sign for benign tumor and a positive sign for malignant tumor. Results can be used for diagnosis between benign and malignant brain tissue. [ABSTRACT FROM AUTHOR]

The Z-scan technique with an Nd: YAG laser at 532 nm was used for detecting the nonlinear optical (NLO) properties of the polyurethane semi-open cell (PUSOC)/SiO2nanocomposite foam. The synthesized foams are also characterized by SEM images and their microstructural features were analyzed. The origin of optical nonlinearity, in this case, may be related to the presence of the two-photon absorption effect and self-defocusing process. Furthermore, the measured values of third-order NLO susceptibilityof the PUSOC/SiO2nanocomposite foam were of the order of 10−7esu. [ABSTRACT FROM PUBLISHER]

We propose for the first time a THz graphene-based electro-optical modulator. The novelty comes from working the device in modulation instability (MI) regime. Multiple embedded graphene layers inside an ionic gel enclosed by a Fabry–Perot resonator provide an enhanced nonlinearity required for starting MI process. Appeared as a pump wave, MI intensely amplifies the modulated wave. Consequently, the operational broad bandwidth and high modulation depth can be obtained. By using the double-gated electrodes’ structure, the ultrafast generation rate of the charge carriers and lowly required driving voltage are attainable for a small footprint. The emerging high sensitivity of the device to the external electric field implies its applicability in non-intrusive electric field sensory tools. Finally, this graphene-based modulator introduces a feasible entity to control the chaotic wave propagation in THz optical communication. [ABSTRACT FROM PUBLISHER]

The CdTe nanocrystals were successfully synthesized using a facile room temperature method with non-toxic and environmentally friendly capping agent. The obtained CdTe nanocrystals were characterized by UV-Vis absorption spectroscopy, transmission electron microscopy, and z-scan technique. A photoluminescence peak with full width at half maximum of around 15 nm could be obtained, which indicates a homogeneous and narrow size distribution for the CdTe nanocrystals. The magnitude and sign of the third-order nonlinear refractive index ( n) and nonlinear absorption coefficient ( β) of the CdTe nanocrystals were determined by using of the closed- and open-aperture z-scan at different intensities, respectively. The negative sign of n indicated that there is a self-defocusing effect in the sample. The nonlinear refractive index, n, and the nonlinear absorption coefficient, β, were in order of 10 cmW and 10-10 cmW, respectively. [ABSTRACT FROM AUTHOR]

In this study, a precise method to evaluate nonlinear optical absorption and refraction of materials using z-scan method based on Fresnel-Kirchhoff integral method (FK method) has been offered. The real electric field of a Gaussian beam passing through a nonlinear sample having both nonlinear absorption and refraction has been investigated using FK method. Subsequently, the z-scan curves have been studied. This is the first time that FK method has been used for calculating the nonlinear absorption coefficient. Additionally, an appropriate numerical curve-fitting method for calculating the nonlinear optical coefficients based on z-scan method has been suggested. Z-scan curves and nonlinear optical coefficients have been obtained for TiO nanoparticles in CW irradiation regime with the particle size ranges from 70 to 90 nm. This is the first experimental study which uses this analytical numerical method. Finally, all calculated results extracted from this new method have been compared with those of the previous methods. [ABSTRACT FROM AUTHOR]

Nematic liquid crystals are the preferred materials for linear and nonlinear optics, where frequently required photosensitivity is provided by appropriate doping. This investigation is concerned with the determination of the Kerr constant of nematic liquid crystal (9CHBT). The temperature dependence of the Kerr constant B for azo dye doped nematic liquid crystals has been studied. The sample has a positive Kerr constant which increases with decreasing of temperature. The linear dependence of the Kerr constant on (T - T*)-1 is found to be in good agreement with the predications of the Landau-de Gennes model. [ABSTRACT FROM AUTHOR]

Nano-particle materials with large optical nonlinearities are in great need for the development of nonlinear optical technology and are being studied intensively in recent years. ZnO nanoparticles have been synthesized by precipitation from zinc acetate in a series of n-alkanols from ethanol to 1-hexanol as a function of temperature. The formation and microstructure of ZnO particles were monitored by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectrum and z-scan technique. We studied the optical limiting effect of ZnO nano-particles. Using a CW He-Ne laser at 632.8 nm. The UV-Visible spectrum of this material shows a 373.5 nm peak. Using the UV-Visible, the band gap of this nano-particle is obtained about 3.31 eV. Also the XRD spectroscopy indicates that the structure is wurtzite hexagonal. Average particle size obtained from SEM analysis about 43nm. Furthermore the nonlinear refractive index, n2, and nonlinear absorption coefficient, β, were measured using close and open aperture z-scan respectively, at peak laser irradiation of 1.743 kW/cm2. Then the nonlinear refraction index of this nano-particle was measured in order of 10-7 (cm2/W) with negative sign and the nonlinear absorption coefficient was obtained in order of 10-3 (cm/W). [ABSTRACT FROM AUTHOR]