International Journal of

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The performance of a polarizing beam splitter based on the one-dimensional photonic crystals (1D-PCs), is theoretically investigated. The polarizing beam splitter consists of a symmetric stack of the low-index quarter-wave plates and the high-index half-wave plates with a central defect layer of air. The linear transmission properties of the polarizing beam splitter are numerically simulated by the transfer matrix method. The results show that the wavelength of the polarizing beam splitter can be tuned by adjusting the thickness of the defect layer of air and the incident angle of light due to the resonant couple of the evanescent waves localized at the interfaces between neighboring layers.

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Thanks to their unique optical and electromagnetic properties, noble-metal nanoparticles are proven very useful in many scientific fields, from nanotechnology to biology, including detection of cancer cells. Irradiated gold nanoparticles, as a nano-smolder could be widely used in biomedical contexts such as tumor therapy. Laser destruction of a cancerous tissue depends on thermal and physical properties of the tissue, therefore temperature quantification of an irradiated metallic nanoparticle in different materials could be followed by interesting applications. In this research we quantify the temperature of irradiated gold nanoparticles in paraffin which is the most commonly used material for embedding of biological tissues in pathology. We have shown that the temperature increase rate for irradiated gold nanoparticles with diameters of 78 nm, 97 nm, and 149 nm are 1.31, 1.40, and 2.28 ◦C/mW, respectively. Considering that the conductivity of a biological tissue is an important parameter on temperature raise and destruction, these results could yield a valuable insight into the cancer therapy.

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In this study, a new numerical method is introduced to obtain the exact shape of output pulse in the chalcogenide fiber Bragg grating (FBG). A Gaussian pulse shape with 173 ps width is used as an input pulse for lunching to a 6.6 mm nonlinear FBG. Because of bistable and hysteresis nature of nonlinear FBG the time sequence of each portion of pulse is affected the shape of output pulse. So we divide the pulse to leading and trailing portion in time. By using bistability curve and Fourier transformation, the exact shape of output pulse is simulated. In comparison of non-unique solution for output pulse in the previous papers, the results of this study have an optional merit.

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In the present work, we investigate the tunability of the magnetic response of a new structure. A lattice of periodically arranged close-packed square conducting rings has been studied for this purpose. Here, instead of enhancing the magnetic activity via resonance, like in split-ring resonators, we concentrate on the analysis of the interactions between these rings. The core idea is to design an array with negligible capacity and to focus on inductive interactions between its building cells. In other words, in this structure, the enhancement of the microscopic process has been attained by the interaction of its building block, i.e. a collective feature has been considered. It is our goal to obtain a sizable magnetic response with this new approach. Our ultimate goal is to demonstrate that the relative magnetic permeability of this architecture could be less than one or even less than zero.

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Recently atomic magnetometers are one of the best tools in biomagnetic measurement such as magnetic field of brain and heart. In this paper, the technology of optically pumped atomic magnetometer based on circularly polarized light absorption pumping is described. We have been investigated a new method for measuring polarization effect in an alkali vapor based on polarized light transmission. In addition several magnetometers’ response factors such as cell temperature, laser’s intensity are introduced and reviewed. Our results show that the difference between absorption of circular and linear light not only depends on polarization, but also in number of polarized atoms.

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In this paper Kolomogorov entropy of a simulated cavity quantum electrodynamics in a multi-partite system consisting of eight quantum dots in interaction with one cavity mode has been estimated. It has been shown that the Kolmogorov Entropy monotonically increases with the increasing coupling strength, which is a sufficient condition for chaotic behavior under ultrastrong coupling regime. The arrangement of the quantum dots is assumed to be in the form of a linear chain where dipole-dipole interactions are considered only between the nearest neighbors.

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Micro size craters were created by interaction of nanosecond laser beam with titanium target in liquid media. The dimension of crater i.e. depth and width is important in some applications such as micromachining. When the interaction occurs in liquid environment, the ablated materials from the target expand into the liquid. The ablated material can affect the interaction process if the ablated material concentration increases. In this paper, we study the effect of ablated materials in liquids on the crater width. The crater dimension was characterized by using an optical microscope. The results show that not only the type of environment liquid is important in the final size of the created craters, but also the laser fluence and the liquid depth in which the interaction takes place is important in the crater size.

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In this study, Highly Oriented Pyrolytic Graphite was ablated in various polar and nonpolar solvents by Q-switched neodymium: yttrium-aluminum-garnet laser (wavelength=1064 nm, frequency=2 kHz, pulse duration=240 ns). Then, the products were examined using Scanning Electron Microscopy and UV-Vis spectroscopy. The images showed that different carbon structures such as cauliflower-like structures in benzene, spiral integrated forms in toluene, organic integrated networks in hexane, and nanoparticles in ethanol were formed. In n-methyl-2-pyrrolidone (NMP), sheets and bulk deformed structures were seen. Also, in Dimethylacetamide, particles in different stages of growth could be detected. The nonlinear optical absorption (NLA) behaviors of the products were investigated by exposing them to a 532 nm nanosecond laser using the Z-scan technique. The saturated NLA coefficient, obtained from structures of NMP and hexane-based synthesized samples, are 1.1×10-8 and 2.4×10-8 cm W-1, respectively. The saturable absorption responses of these samples were switched to the reverse saturable absorption responses in the other synthesis mediums. The maximum nonlinear absorption coefficient of 10.2×10-8 cm W 1 was measured for spiral integrated superstructures, produced in the toluene medium.

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One of the solutions of the Helmholtz equation is the vortex beams. In the recent decades, production and applications of these types of beams have found serious attentions. Determination of the vortex beam topological charge and its sign are very important issues. Odd number of reflections of the vortex beam changes its vorticity. In this paper, we have used a q-plate to generate a vortex beam from a plane wave of a He-Ne laser beam and a two-channel moiré based wavefront sensor is used to measure wavefront gradient of the vortex beam. In two different arrangements the vortex beam experience odd and even number of reflections, respectively, and from the moiré pattern deformations the topological charge of the vortex beam and its sign are determined.

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We have proposed a new ultra-compact optical demultiplexer based on metal-insulator-metal plasmonic waveguides aperture-coupled to the ring resonators. Our proposed device has high performance, small footprint, and high potential for integration and development to more channels.

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Nanocrystallite α-cordierite glass-ceramics are synthesized using a modified Pechini method. The structural and lattice modes of the products are investigated via XRD and Micro Raman back-scattering spectroscopy. The Debye-Scherrer formula is used to confirm the grain sizes estimated by the SEM slides. Dielectric coefficients calculation and DTA analysis are used to study the synthesized nanocrystallites properties.

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We study the focusing properties of a two dimensional complex square-lattice photonic crystal (PC) comprising air holes immersed in Ge medium. The finite difference time domain (FDTD) method is utilized to calculate the dispersion band diagram and to simulate the image formation incorporating the perfectly matched layer (PML) boundary condition. In contrast to the common square PCs with the same air filling factor, the frequency corresponding to the effective negative refraction occurs in the second photonic band and the spatial image resolution is improved.

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In this paper, we propose a theoretical scheme for the generation of non-classical states of the cavity field in a system of a single trapped atom via controlling the Lamb-Dicke parameter. By exploiting the super-operator method, we obtain an analytical expression for the density operator of the system by which we examine the dynamical behaviors of the atomic population inversion, the phase-space Husimi Q-function as well as the von Neumann quantum entropy of the cavity-field. The results reveal that at certain periods of time one of the cavity-field quadratures may be squeezed and the two sub-systems of the trapped atom and the cavity field are entangled. Moreover, we find that the atomic spontaneous emission and the cavity-field damping destroy the nonclassical characteristics of the cavity field.

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The identification and concentration of heavy metals, which may be so harmful for the body, is determined by the method of calibration-free laser-induced breakdown spectroscopy using a special strategy. First, the plasma temperature is obtained using the Boltzmann plot. Then, a line with an inappreciable self-absorption is considered for each element as the reference. The modified intensities of other lines of the element are calculated through their self-absorbed intensities in terms of the reference intensity. The plasma temperature is again computed by line pair ratio method. This procedure is carried out by an iterative algorithm until the self-absorption coefficient of selected lines converges on one. In the last step, the corrected temperature is evaluated by the Boltzmann plot drawn using true (non self-absorbed) line intensities of each element. The concentration of the elements is finally determined by the corrected temperature and intensities. The results indicate that the accuracy of this method in determining the concentrations is significantly better than the normal way.

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By introducing a thin ZnO layer as an optical spacer, we have demonstrated that inserting this layer between an active layer and a reflective electrode results in a re-distribution of the optical electric field inside bulk heterojunction solar cells. A theoretical analysis by optical modeling showed that the thin ZnO layer could shift the position of the maximum of the electric field into the absorbing layer. Theoretical calculations were compared with experimental results for devices with and without an optical spacer. By using a ZnO optical spacer layer, a significant increase was observed in the short circuit current density of J-V curves. This increase might be due to harvesting more lights and also hole-blocking by the ZnO layer. Both electrical and optical characteristics of the device provided improved results in the power conversion efficiency of the bulk heterojunction solar cell up to 3.49%.

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In this paper, considering optical feedback as an optical injection, and taking in to account round-trip time role in the external cavity, a standard small signal analysis is applied on laser rate equations. By considering the relaxation oscillation (f2) and external cavity frequencies (f) ratio for semiconductor laser, field amplitude response gain, optical phase and carrier number for long external cavities (LEC) and short external cavities (SEC) are obtained. Laser output intensity and resonance peak dynamics have been shown by bifurcation diagrams. Furthermore, the effects of some control parameters, such as enhancement factor, pumping current and feedback strength, on response gain have been discussed in short and long external cavities. As a result, in optical injection, for SEC, compared to LEC, more varied dynamics are observed. Also, higher values of the response gain peak in SEC, in comparison with LEC, make SEC to be affected more by the injected beam. SEC provides greater bandwidth, and also better performance in the range of compared to LEC.

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In this paper, a tapered tip optical fiber probe sensor for localized refractive index (RI) measurements is presented. This sensor’s interaction with analytes is confined to a few micro-meters which makes it a promising candidate for in-vivo or even intra-cellular RI monitoring. This tapered tip was simply fabricated by etching optical fiber with hydrofluoric acid to a conic shape with a sub-micrometer aperture. The sensor was calibrated for RI measurement using different concentrations of NaCl in water. Limit of detection of 6.7×10^-5 RIU was achieved for this low-cost sensor.

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A modulated holding beam shining a VCSEL above threshold can improve modulation bandwidth by adjusting the semiconductor laser’s relaxation oscillation frequency. The improved modulation characteristics are accompanied by reduced damping rate. By choosing correct parameters, dynamical behavior of system and cavity solitons is changed.

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Polyurethane closed cell (PUCC)/SiO2 nanocomposites have been prepared by using in situ polymerization approach. The third-order optical nonlinearities of PUCC/SiO2 nanocomposites, dissolved in DMF are characterized by Z-scan technique at the measurement wavelength of 532 nm. The nonlinear refractive (NLR) indices and nonlinear absorption (NLA) coefficients of samples were calculated from closed and open aperture Z-scan in the order of 10-8 with negative sign and 10-5 , respectively. The origin of optical nonlinearity in this case may be attributed due to the presence of two photon absorption (TPA) effect. The synthesized samples were examined by optical microscopy, SEM imaging and Raman spectroscopy. All the results related to NLO properties, suggest that PUCC/SiO2 may be a promising candidate for the application to optical limiting in the visible region.

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Based on transformation optics‎, ‎we propose an illusion device that can make‎ ‎objects look much smaller and different than they actually are‎. ‎In particular‎, ‎the device has a capability to hide a large object (like an elephant) into a‎ ‎small one (like a matchbox)‎. ‎Compared to previous proposals for illusion‎ ‎devices‎, ‎there is no requirement for negative refractive index or for speed of‎ ‎light going to infinity as in Euclidean invisible cloaks‎. ‎We demonstrate the‎ ‎functionality of the device by full wave simulations‎.