International Journal of

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We investigate theoretically the high-order harmonic spectrum extension and numerical generation of an intense isolated attosecond pulse from He+ ion irradiated by a two-color laser field. Our simulation results show that the chirp of the fundamental field can control HHG cutoff position. Also, these results show that the envelope forms of two fields are important factors for controlling the resultant attosecond pulses. Besides, the effects of relative intensity are investigated. As a result, by using the optimized conditions an intense isolated 126-as (attosecond) pulse can be observed

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In this paper, a fractal photonic crystal fiber (F-PCF) based on the 1st iteration of Koch fractal configuration for optical communication systems is presented. Complex structure of fractal shape is build up through replication of a base shape. Nowadays, fractal shapes are used widely in antenna topics and its usage in PCF has not been investigated yet. The purpose of this research is to compare normal photonic crystal fibers (N-PCFs) with F-PCFs through the simulation and optimization procedure based on the finite element method (FEM). The effective mode index of the fundamental mode is found for different PCF structures. In addition, dispersion properties of F-PCF are numerically calculated and compared with N-PCF.

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One concern in using photonic band-gap fiber (PBGF) as a gas sensor is the response time. In this type of the gas sensors, response time is the time required for gas to diffuse into the hollow-core. So considering a large hollow-core PBGF (HC-PBGF), the response time can be significantly reduced. But in the large HC-PBGF, the fundamental issue is the presence of higher order modes (HOMs). Sometimes the leakage loss of the HOMs is comparable to those of the fundamental mode. So in order to suppression of the HOMs, six small-cores with reasonable radius were incorporated in the cladding of the proposed fiber. In other words, due to resonant-coupling mechanism of HOMs in central core with fundamental mode of outer cores, the leakage loss of the HOMs can be enhanced. Considering optimum parameters such as hollow-core radius, air filling factor, and the distance between the center-to-center of two adjacent air holes, the small-cores are surface-mode-free and proposed structure can be considered effectively single mode. So at the wavelength of 1550nm the relative sensitivity of the gas sensor was improved to 97%. The results proved the ability of proposed design as a sensitive gas sensor with low response time.

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In this paper, we numerically simulated a glass-based all-optical 1×N power splitter with eleven different configurations using soliton breakup in a nonlinear medium. It is shown that in addition to reconfigurability of the proposed splitter, its power splitting ratio is tunable up to some extent values too. Nonlinear semivectorial iterative finite difference beam propagation method (IFD-BPM) with inclusion of two photon absorption (TPA) effects is applied to simulate the soliton propagation at different mode power. It is shown that operation of the proposed splitter depends on input mode power and an all-optical reconfigurable-tunable functional device is designed with nonlinear optical (NLO) property of a simple structure.

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Photonic crystal design procedure for negative refraction has so far been based on trial and error. In this paper, for the first time, a novel and systematic design procedure based on physical and mathematical properties of photonic crystals is proposed to design crystal equi-frequency contours (EFCs) to produce negative refraction. The EFC design is performed by the help of rectangular stair-case (RSC) photonic crystals. The RSC crystal is then converted to more common structures like pillar crystals by matching Fourier coefficients of periodic electric permittivity. Methods to design common crystals which have approximately equal Fourier components to the RSC crystal are also discussed. The proposed procedure can be used to design metamaterials without the difficulties of large trial and error. The devised procedure can also be applied in designing other structures involving photonic crystals.

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In this work, applicability of Particle in Cell-Monte Carlo Collisions (PIC-MCC) simulation method for better understanding of the plasma physical mechanisms and real important aspects of a plasma column driven by surface wave plasma discharges that is used in plasma antennas is examined. Via the implementation of geometry and physical parameters of the plasma column to an Object Oriented PIC-MCC code, the plasma density, electrical conductivity, plasma kinetic energy and electric field inside the plasma column as its essential properties are obtained. The gas within the plasma column is taken to be argon which is kept at the low operational background pressures. The radial increasing and axial decreasing of the electric field in the plasma column is observed. Moreover, the plasma density reduces radially, while it is maximized along the axial positions. It is seen that, the density of charged particles and their corresponding current densities are maximized at the positions closer to the surface wave launcher.
 

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high harmonic generation is a useful tool for the generation of short, intense attosecond pulses. In order to simulate high harmonic generation, we performed a numerical solution to the time dependent Schrödinger equation. by considering dipole approximation, we predicted generation of a 53 attosecond pulse. In order to see the time and frequency of emission of attosecond pulse, we exploit time frequency analysis. On the other hand, because of uncertainty between time and frequency, it would be of high importance whether which analysis is been applied. our studies show that Gabor analysis exhibits the least uncertainty between time and frequency components. And at least, we set the balance between time and frequency distribution by altering the window size.  

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This work presents ZnO nanorods coated multimode optical fiber sensing behavior in response to ethanol solution. The sensor operates based on modulation of light intensity which arises from manipulation of light interaction with the ambient environment in sensing region. For this purpose, two steps are experimentally applied here; etching and then coating fiber with ZnO nanorods to provide stronger evanescent waves causing an enhanced interaction. Long length of fiber (15 mm) was etched uniformly and then well-ordered ZnO nanorods were grown hydrothermally on the core of optical fiber. Fiber coated with ZnO demonstrated an enhanced sensing performances such that response time decreased to 0.6s, linearity increased to 97% and sensitivity improved. Applicable features of the proposed device such as fast response time and high linearity make it favorable candidate for fiber optic sensing applications.

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We solved one dimensional Schrodinger equation in a H₂⁺ molecular environment by using 3 femtosecond homogeneous and nonhomogeneous laser fields. In homogeneous case, we found out that larger inter nuclear distances result in earlier ionization and also more instability in the wave packet. We deducted that the more the instability is, the more modulated the power spectrum will be. So, by choosing a fixed 1.96 atomic units inter nuclear distance, we investigated high harmonic generation in both linear and nonlinear nonhomogeneous laser pulses. We observed that in comparison with the linear case, in nonlinear one, the plateau possessed higher intensity harmonics. On the other hand, in this case, cutoff order occurred on higher frequency. By superposing several harmonics near cutoff region, we predicted the generation of a 73 attosecond pulse.

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In this article, the optical properties of silver cubic-shape nanostructures (SCNs) were analyzed by employing the discrete dipole approximation (DDA) in aqueous media. The absorption, dispersion and extinction cross-sections of these nanostructures were calculated based on the wavelength change of the incident light in the visible and near infrared region. Moreover, the height change, wavelength and full width at half maximum (FWHM) of extinction cross-section peaks (from plasmon resonances) based on the size of nanoparticles and the environment dielectric constant were surveyed. The results showed that only two peak modes, named dipole peak and quadrupole peak, exist in this spectrum, such as spherical particles.

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In this work we applied a Bessel beam (BB) to a layer of turbid medium. We applied the Monte Carlo simulation. This work emulates a tissue under surgery by a Bessel beam. Actually, the BB introduces less divergence. Thus it will be good for surgery. On the other part this is done by Monte Carlo simulation. Upon simulation we got family of curves to characterize absorption, reflection and scattering of this layer. Where we got numerical values of absorption, transmission and reflection of this layer. The curves are for layer thickness that varies along with varying scattering coefficient, absorption coefficient and anisotropy factor.

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In this work, a two-dimensional square periodic array was successfully transferred onto a rigid glass substrate during an innovative and simple-design two-step process of pattern transferring using Kapton tape and plasma technology. Flexible and stretchable, Kapton tape was selected for pattern transferring onto the glass for the first time herein; in parallel, the vacuum plasma treatment was utilized to improve surface adhesion properties and aid the pattern transferring process. The proposed 2D square plasmonic array supported the plasmon-induced transparency (PIT) phenomenon, which is caused by the excitation of surface plasmon resonances. The current study simulated the fabricated plasmonic structure using the finite-difference time-domain (FDTD) method and investigated the propagation of surface plasmon polariton (SPP) and cavity modes which enhanced transmission. This fabrication technique can offer new insights for micro/nanofabrication technology.