Optics and Photonics Society of Iran

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Abstract- In this paper, the graphene-Ag/Poly(vinyl chloride) nanocomposite has been prepared by a solution method. Then, the optical constants such as absorption coefficient, extinction coefficient, refractive index, optical band gap (Eg), optical conductivity and dielectric constant were calculated by considering the results of reflectance and transmittance spectra in the UV-Visible wavelength region. The optical band gap of the pure polymer was obtained about 3.79 eV. Finally, it was observed that, adding filler nanoparticles to the polymer matrix reduces the optical band gap of the polymer about 20%.

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We consider a plane metamaterial with unit cells composed of short wire pairs and continuous wires. We investigate the effect of the value of the dielectric constant of the dielectric layer between short wires on the effective refractive index of the structure. By increasing the value of the dielectric constant, the effective refractive index of the structure changes from negative values to positive values. Inspired by this phenomenon, we can construct a metamaterial that its effective refractive index changes sign as the intensity of the incident light is increased.

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Abstract-In this manuscript preparation of gold nanoparticles using the pulsed laser ablation of gold target in water has been described. Optical absorption spectrum of nanoparticle suspensions in water has been observed and nanoparticles sizes have been analyzed by transmission electron Microscopy. The optical limiting measurement method is explained and obtained results are presented. The results of optical limiting experiments with CW ND YAG laser beam (wavelength 532nm) indicate linear response of samples when input power is below about 70 mW and nonlinear respons to large powers than this limitation. Results reveal that thermal nonlinear refraction index due to surface plasmon resonance is the main responsible for the limiting behavior of the metallic nanoparticles suspensions.

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Abstract: Intersubband optical transitions in superlattice nanowires with graded interface are investigated analytically. In this way the effective mass approximation is used to calculate the electronic wave function and energies numerically. Density matrix approach in addition with iterative method is used to obtain the (linear and third order nonlinear) change in the refractive indices (RI) and absorption coefficient(AC) analytically. The effect of size, magnetic field and the interface width are investigated. It is found that nonlinear parts of RI and RA have large contribution and must be considered in calculation of the total RI and RA.

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There are various methods for determination of optical parameters of thin films. One of these methods is optimization method. First we practically deposited a HfO2 thin film onto Ge Substrate by vacuum evaporation technique and transmittance spectra was measured in the infrared region. After the exact studies, a computer program written in MATLAB for Genetic Algorithm(GA) optimization method and its results test with exact values from Essential Macleod software . By using this method, the thin film sellmeier coefficient were optimized and subsequently we could extract optical constants(refractive index and extinction coefficient) of sample with good accuracy in the NIR region. Comparision data of this method with past researchs gave rise this result: the GA is an almost exact method for determination of thin films optical parameters.

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Abstract- in this paper refractive index measurements of the optical fibers is investigated theoretically and experimentally by the refractive near field approach. An experimental setup has been designed according to the consideration of light propagation in the optical fibers and calculation of the geometrical parameters for this measurement. The experimental results for SMF28 optical fiber have been shown that an accuracy in the order of is achieved.

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In this paper we have investigated the Rashba spin-orbit interaction effects on the optical properties of a spherical quantum dot with infinite potential. In this regard energy eigenvalues and functions are calculate without considering the spin-orbit interaction. by means of new energy eigenvalues and functions, transition dipole moments, optical absorption coefficient and refractive index are calculated. Results show that spin-orbit interaction and it's strength have considerable effects on the optical properties of the system.

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Under strong laser illumination, few-layer graphene exhibits a nonlinear phase shift. Here, we distinguish this nonlinear optical effect which used to be named nonlinear refractive index. We show that fabricated graphene based on Q-switched Nd:YAG laser ablation possesses a giant nonlinear refractive index in comparison with graphene powders fabricated by chemical method.

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The effect of geometrical anisotropy is numerically investigated on the linear and nonlinear optical refractive index changes of a GaAs quantum dot which is located at the center of a Ga1-xAlxAs cylindrical nano-wire. The finite difference approximation has been used for obtaining energy eigenvalues and corresponding wave functions. Also, the compact density matrix formalism is applied to investigate linear, third order nonlinear and total optical refractive index (RI) changes. The optical properties are calculated as a function of the incident photon energy for different ellipsoid aspect ratio and dot radius. The results clearly reveal that the dot anisotropy plays an important role in determining the magnitude of nonlinear RI changes which enable us to adjust saturation condition. We also found that the dot anisotropy shifts optical spectrum towards both lower and higher energies which depend on the shape of dot (spherical, prolate or oblate quantum dot) and dot radius.

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In this paper the antibacterial properties of silver nanoparticles (SNPs) against the Escherichia coli (E.coli) by culturing the organisms in liquid broth in the presence different concentration of SNP was studied by optical fiber sensor. The sensor was fabricated using heat-pulling method by CO2 laser and bacteria immobilized on the optical fiber surface. Then the sensor was surrounded with different concentration of SNP. Also, due to interaction of SNP and immobilized bacteria on the optical fiber surface, changed the effective refractive index around the fiber and this affects the evanescent field leading to changes in optical throughput. The results show that E.coli growth was inhibited by different concentrations of SNP. The inhibition rate of the E. coli growth for SNP concentrations in the range of 0 to 50 μg ml-1 were measured to be from 58.0×10-2h-1 to -35.0×10-2 h-1 and from - 1.3×10-3 h-1 to - 8.88×10-3 h-1for colony counting and optical fiber biosensor, respectively. This novel sensing method, promises new application such as rapid analysis of antibacterial effects of SNPs. 

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The diffusion coefficient of liquid-liquid has been measured using the Fresnel diffraction from a phase step. As a phase step in transmission mode, a glass plate is immersed in the diffusion cell. The plate is illuminated by a monochromatic parallel beam of a He-Ne laser and the diffraction pattern which is formed on a surface perpendicular to the beam propagation direction is recorded using a CCD. During the diffusion process, the refractive index distribution inside the diffusion cell varies by time and changes the intensity distribution on the diffraction pattern. The Fourier transform method is used to find the phase distribution and the refractive index profile which provides the diffusion coefficient.

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--Absorption of a plane laser beam in a themocapillary nematic liquid crystal cell and consequent molecular director reorientation due thermomechanical effect is studied. It was shown that significant changes can occur in the index of refraction due to thermomechanical effect.

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Effect of spatial temperature profile, which can be introduced due to illumination of an amorphous material by a focused ultra-short laser pulse, on different physical parameters of the material is studied by numerically solving thermoelastic wave equations by using Finite Element Method. It is observed that temperature profile in the focal region has significant effect on the spatial and temporal behavior of the displacement, strain, stress, and consequently, refractive index of the material. Therefore, assuming temperature profile as uniform or similar to the initial laser pulse profile may lead to inaccurate results, and are should take into account nonlinear effects during pulse propagation and the resulting temperature profile.

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A differential mode sensing scheme for microsphere refractive index sensors, is proposed and demonstrated that can substantially suppress environmental noises to improve the detection limit about 30 times. This sensing scheme has high compatibility with any other microcavity sensors to get lower biosensing limit.

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Studying nonlinear optical response of each part of a compound, not only leads to investigation of a specific material in various conditions, but also could be a way to find the best mixture and optimum concentration of additives for optical response enhancement. In this work, using dual-arm Z-scan technique, the nonlinear refractive index of Disperse- Red-1 organic dye molecules inside of polymeric nanocapsules was measured and compared with total condition.

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Application of titanium dioxide nanoparticles in low concentration has significant improvement in enhanced oil recovery which this observation needs new models. In this research, light scattering of nanoparticles with diameter of 35 nm in different concentration were measured and based on Debye plot molecular weight and 2nd virial coefficient were calculated. For this purpose, refractive index increment was needed which was measured using Michelson interferometer method. Based on 2nd virial coefficient, the osmotic pressure of the nanoparticles was calculated. The result indicates that in low concentration of nanoparticles this pressure is not the main mechanism of oil detaching from rock surface.

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Measuring optical parameters of thin films with high accuracy is a challenge in modern science and industry. We introduce a new method to obtain refractive index and thickness of transparent dielectric layer. This method is based on Fresnel diffraction from the phase step in transmission. By recording and analyzing the diffraction pattern versus incident angle, the diagram of visibility versus incident angle is obtained. Therefore by fitting simulated data to experimental ones (visibility versus incident angle), refractive index and height of phase step is determined. The uncertainties of determination of refractive index and thickness are about 0.5% and 0.1%, respectively.

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When a coherent light passes through a diffraction grating, the image of the grating is formed at the Talbot distances. If we place a rough interface after a diffraction grating, the reflected light also forms the image of the grating at Talbot distances but with less contrast. This contrast decreases proportional to surface roughness. In transmitted light from a rough surface, the contrast of the Talbot images depends on the surface roughness and refractive index of material. In this article It is shown theoretically and examined experimentally that the refractive index of the material with a rough interface can be determine by measuring the contrast of the reflected and transmitted light form a rough surface at Talbot distances.

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In this paper, the sensitivity of refractive index measurement using prisms with the metal coating in the phase sensitive optical sensors which operate based on the total internal reflection, has been investigated. It has been shown that the variations of phase difference between two p-polarized and s-polarized reflected waves with the refractive index of the test material in the case of the prism with a metal coating is higher than that of the non-metallic coating. This is due to the excitation of surface plasmons at the interface between the test material and the thin metal layer. Since, one can obtain the refractive index of a test material by measuring this phase difference with the phase-shifting interferometer, the refractive index measurement using the prisms with metal coating has higher sensitivity.

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In this paper experimental results concerning far field diffraction of Fe3O4 nanoparticles produced by ablating iron target in distilled water using the first harmonic of an acousto-optically Q-switched Nd:YAG laser are presented. In the present research we measured nonlinear refractive index of Fe3O4 nanoparticles using a single beam z-scan technique to compare with the results of far field diffraction. In both experiment we used a He-Ne CW laser beam operated at 632.8 nm to obtain nonlinear refractive index of Fe3O4 nanoparticles.