Publication Date: 2015
Nanoscale (20403372)7(26)pp. 11379-11385
We design a compact, all-optical THz wave generator based on self-modulation in a 1-D slab photonic crystal (PhC) waveguide with a single sub-nanometer graphene layer by using enhanced nonlinearity of graphene. It has been shown that at the bandgap edge of higher bands of a 1-D slab PhC, through only one sub-nanometer graphene layer we can obtain a compact, high modulation factor (about 0.98 percent), self-intensity modulator at a high frequency (about 0.6 THz) and low threshold intensity (about 15 MW per square centimeter), and further a compact, all-optical THz wave generator by integrating the self-modulator with a THz photodiode or photonic mixer. Such a THz source is expected to have a relatively high efficiency compared with conventional sources based on optical methods. The proposed THz source can find wide applications in THz science and technology, e.g., in THz imaging, THz sensors and detectors, THz communication systems, and THz optical integrated logic circuits. © The Royal Society of Chemistry.
Publication Date: 2004
Proceedings of SPIE - The International Society for Optical Engineering (1996756X)5249pp. 249-260
A systematic design method for quasi-symmetrical wide angle systems is presented. The method starts with thin lens predesign of half of the system using most available glasses. The aperture stop position is determined for reducing astigmatism and the system is made symetrical about it for eliminating Coma, Lateral colour and Distortion. Finally the system is optimized using Eikonal software for infinite conjugate.
Publication Date: 2013
European Physical Journal D (14346060)67(12)
A four-body approach based on the three-Coulomb distorted wave (3CDW) model is applied to study of the electron-impact single ionization of helium atoms. Triply differential cross sections (TDCS) are calculated for different values of the incident and ejection energies and various amounts of the scattering angles. The ejection angular distribution of the TDCS in general exhibits two peaks, binary and recoil peaks. The obtained results are compared with the available experimental data as well as other theoretical predictions. The comparison shows a good agreement between the present calculations and the measurements. Also, the obtained results are compatible with the other theories. © 2013 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.
Publication Date: 2021
Journal of Physics A: Mathematical and Theoretical (17518113)54(21)
In this paper, we first try to shed light on the ambiguities that exist in the literature in the generalization of the standard linear response theory (LRT) which has been basically formulated for closed systems to the theory of open quantum systems in the Heisenberg picture. Then, we investigate the linear response of a driven-dissipative optomechanical system (OMS) to a weak time-dependent perturbation using the so-called generalized LRT. It is shown how the Green's function equations of motion of a standard OMS as an open quantum system can be obtained from the quantum Langevin equations (QLEs) in the Heisenberg picture. The obtained results explain a wealth of phenomena, including the anti-resonance, normal mode splitting and the optomechanically induced transparency (OMIT). Furthermore, the reason why the Stokes or anti-Stokes sidebands are amplified or attenuated in the red or blue detuning regimes is clearly explainedwhich is in exact coincidence, especially in theweak-coupling regime, with the Raman-scattering picture. © 2021 Institute of Physics Publishing. All rights reserved.
Publication Date: 2023
IEEE Sensors Journal (1530437X)23(14)pp. 15570-15577
With strong evanescent waves, optical microfibers (MFs) provide guided lights the ability to directly interact with surrounding environments, whereby several fiber optics chemical sensors have been realized. In this study, based on MFs external refractive index (RI) sensitivity, a multimode optical fiber (MMF) specklegram RI sensor with MMF-MF-MMF configuration is presented. As the MF Section is exposed to the liquids of different RIs (in the range of 1.333-1.368), the interaction between the liquids and evanescent waves modulates the guidance status of the MF, thereby changes the excited modes within the end MMF Section and affects the output speckle pattern accordingly. The evaluation of the functionalities of the MFs with different waist diameters (11, 18, 33, and 42 μ m ) shows that the MF with 33- μ m waist diameter results in the highest output specklegram RI sensitivity, which has been quantified by the zero-mean normalized cross correlation coefficient (ZNCC). Moreover, the response time and sensitivity of the proposed fiber specklegram sensor (FSS) have been simultaneously improved by applying spacial filter on the captured speckles. The RI sensor has also been studied for the temperature detection and showed 0.013°C-1 linear sensitivity within the range of 25 °C-65 °C. Finally, the theoretical analysis of the supported modes by the MFs of the specified waist diameters verifies that 33- μ m sample with high number of guided modes and strong total evanescent waves is the optimum case for the MMF-MF-MMF specklegram RI sensor. © 2001-2012 IEEE.
Publication Date: 2010
Annals of Physics (1096035X)325(9)pp. 1976-1986
A canonical quantization scheme is represented for a quantum system interacting with a non-linear absorbing environment. The environment is taken anisotropic and the main system is coupled to its environment through some coupling tensors of various ranks. The non-linear response equation of the environment against the motion of the main system is obtained. The non-linear Langevin-Schrödinger equation is concluded as the macroscopic equation of motion of the dissipative system. The effect of non-linearity of the environment is investigated on the spontaneous emission of an initially excited two-level atom imbedded in such an environment. © 2010 Elsevier Inc.
Publication Date: 2012
Brazilian Journal of Physics (16784448)42(3-4)pp. 172-179
The differential and total cross sections for electron capture by positrons from helium atoms are calculated using a first-order distorted wave theory satisfying the Coulomb boundary conditions. In this formalism, a parametric potential is used to describe the electron screening in a consistent and realistic manner. The present procedure is self-consistent because (a) it satisfies the correct boundary conditions and post-prior symmetry, and (b) the potential and the electron binding energies appearing in the transition amplitude are consistent with the wave functions describing the collision system. The results are compared with the other theories and with the available experimental measurements. At the considered range of collision energies, the results agree reasonably well with recent experiments and theories. © 2012 Sociedade Brasileira de Física.
Publication Date: 2011
Annals of Physics (00034916)326(4)pp. 968-978
This paper presents a method to describe dynamics of an ion confined in a realistic finite range trap. We model this realistic potential with a solvable one and we obtain dynamical variables (raising and lowering operators) of this potential. We consider coherent interaction of this confined ion in a finite range trap and we show that its center-of-mass motion steady state is a special kind of nonlinear coherent states. Physical properties of this state and their dependence on the finite range of potential are studied. © 2010 Elsevier Inc.
Publication Date: 2011
Optica Applicata (00785466)41(4)pp. 897-909
In this paper, we consider properties of cosh-squared-Gaussian beam passing through ideal and apertured fractional Fourier transforms (FRFT) systems. We use Collins integral formula and the fact that a hard aperture function can be expanded into a finite sum of complex Gaussian functions. These studies indicate that the normalized intensity distributions with FRFT order are periodic. The variation period is 2 and is independent of the impact of aperture.
Publication Date: 2006
Few-Body Systems (01777963)39(1-2)pp. 11-25
Off-the-shell anomalous factors of the two-body Coulomb transition matrices appear in the integral form of the Faddeev second-order nuclear-electronic amplitude, for proton-hydrogen charge transfer scattering in a typical nlm → n′l′m′ transition. A symmetric-impulse approximation (SIA) is applied to eliminate these factors and an induction method is proposed to analytically calculate the remaining integrals. The nuclear-electronic amplitude is derived for the general case, and for totally symmetric collisions, in terms of generalized hypergeometric functions of two variables, F 4, and of one variable, 3 F 2, respectively. The angular distribution of the second-order nuclear-electronic charge transfer amplitude shows the Thomas mechanism as a peak or a hump for symmetric and asymmetric collisions. There also exists a peak in the forward angular distribution of the second-order nuclear-electronic amplitude, which partly cancels the kinematic peak in the angular distribution of the charge transfer differential cross sections.
Publication Date: 2005
European Physical Journal D (14346060)32(3)pp. 397-408
In this paper we propose a theoretical scheme to show the possibility of generating various families of nonlinear (f-deformed) coherent states of the radiation field in a micromaser. We show that these states can be provided in a lossless micromaser cavity under the weak Jaynes-Cummings interaction with intensity-dependent coupling of large number of individually injected two-level atoms in a coherent superposition of the upper and lower states. In particular, we show that the so-called nonlinear squeezed vacuum and nonlinear squeezed first excited states, as well as the even and odd nonlinear coherent states can be generated in a two-photon micromaser. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2005.
Publication Date: 2015
IEEE Journal of Quantum Electronics (00189197)51(8)
In this paper, we present a theoretical model that describes the performance of a specific oven configuration used to actively control the effect of thermal dephasing on the output characteristics of a high-power single-pass second-harmonic generation (SHG) in a MgO:sPPLT nonlinear crystal. The provided model is based on using step and slope oven configurations and making a quantitative comparison with the recent results obtained by using open-top oven scheme. It is found that in the slope oven scheme the SHG power is enhanced by 190% at a fundamental power of 50 W, indicating the significance of the represented model. Eventually, the merit of the proposed slope oven indicated through saturation control in the generation of high-power SH radiation. © 1965-2012 IEEE.
Publication Date: 2014
Applied Optics (21553165)53(1)pp. 132-140
We investigate numerically the feasibility of phase aberration correction in a wavefront sensorless adaptive optical system, based on the imperialist competitive algorithm (ICA). Considering a 61-element deformable mirror (DM) and the Strehl ratio as the cost function of ICA, this algorithm is employed to search the optimum surface profile of DM for correcting the phase aberrations in a solid-state laser system. The correction results show that ICA is a powerful correction algorithm for static or slowly changing phase aberrations in optical systems, such as solid-state lasers. The correction capability and the convergence speed of this algorithm are compared with those of the genetic algorithm (GA) and stochastic parallel gradient descent (SPGD) algorithm. The results indicate that these algorithms have almost the same correction capability. Also, ICA and GA are almost the same in convergence speed and SPGD is the fastest of these algorithms. © 2014 Optical Society of America.
Publication Date: 2011
Optics Communications (00304018)284(8)pp. 2230-2235
We investigate the potential of plasmonic resonance in metal nanocomposite materials for the design of photonic crystal all optical switches by numerical methods. We study the absorption effect of the plasmonic resonance on the Fano resonances of one dimensional photonic crystal slabs covered by a metal nanocomposite layer. It is shown that the absorption reduces the contrast of the Fano resonances. However, for adequate metal nanoparticle concentrations it is possible to achieve both sufficiently sharp Fano resonance and strong Kerr nonlinearity, which provides a suitable condition for the design of high contrast and low threshold switches. © 2011 Elsevier B.V. All rights reserved.
Publication Date: 2020
Proceedings of SPIE - The International Society for Optical Engineering (1996756X)11460
In recent decades, research in the field of optoelectronics has attracted great interest. Modulators are one of the most usable optical components in the optical communication systems. The most important parameters for a modulator are high modulation speed, small footprint, and large optical bandwidth. In this paper we design and fabricate an all-optical intensity modulator based on optical microfiber in which graphene oxide replaces the clad of microfiber. We chemically etched the clad of multimode optical fiber. Then we coated aqueous solution of graphene oxide with concentration 5 mg/ml on the microfiber that has 90° curvature. The graphene oxide was irradiated directly by the pump laser (power=500 mW) at wavelength 405 nm from outside the microfiber. We were able to achieve a maximum modulation depth of 27.3% by graphene oxide. The modulator has been built has many advantages such as compatibility with optical communications, easy fabrication, and low cost. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
Publication Date: 2017
Optics Communications (00304018)383pp. 159-164
The all-optical switch is realized based on nonlinear transmission changes in Fano resonance of 2D photonic crystals (PhC) which enhances the light intensity on the graphene in PhC; and in this study, the graphene layer is used as the nonlinear material. The refractive index change of graphene layer leads to a shift in the Fano resonance frequency due to the input light intensity through the Kerr nonlinear effect. Through finite-difference time-domain simulation, it is found that the high performance of all-optical switching can be achieved by the designed structure with a threshold pump intensity as low as MW/cm2. This structure is featured by optical bistability. The obtained results are applicable in micro optical integrated circuits for modulators, switches and logic elements for optical computation. © 2016
Publication Date: 2022
Applied Physics B: Lasers and Optics (09462171)128(12)
The present study discussed a theoretical model to simulate the interaction of an ultra-short femtosecond laser pulse with a slab of neutral Ar gas. The calculation was based on using the Particle in Cell-Monte Carlo Collision (PIC-MCC) method to investigate the possibility of infrared emission. It was found that besides several emissions that are inevitably obtained from a high-density Ar-based plasma medium, resonance radiation can be achieved at about 165 THz whenever the stimulated Raman scattering (SRS) based half-harmonic and rippled density wavenumber are involved in phase match condition with the fundamental laser frequency. Among several parameters examined to amplify the resonance emission, the symmetry breaking of electric field (SBEF) and turning up the input intensity to about 1018 W/cm2 proved more efficient infrared emission. It turned out that compared to the SBEF effect, an almost three times stronger infrared intensity can be obtained using more intensive laser pulses. The transverse profile for half-harmonic emission and resonant radiation is presented. It is observed that, the infrared radiation has an off-axis profile. At an intensity of 1018 W/cm2, the effects of hot electrons and the nonlinear Kerr refractive index have been presented. It was found that these two parameters limit the generation mechanism at the beginning of the plasma and at the end of the interaction medium, respectively. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2017
Journal of the Optical Society of America B: Optical Physics (07403224)34(12)pp. 2519-2527
In this paper, we theoretically propose an optomechanical scheme to explore the possibility of simulating the propagation of the collective excitations of the photon fluid in a curved spacetime. For this purpose, we introduce two theoretical models for two-dimensional photon gas in a planar optomechanical microcavity and a two-dimensional array of coupled optomechanical systems. In the reversed dissipation regime of cavity optomechanics where the mechanical oscillator reaches equilibrium with its thermal reservoir much faster than the cavity modes, the mechanical degrees of freedom can adiabatically be eliminated. The adiabatic elimination of the mechanical mode provides an effective nonlinear Kerr-type photon–photon interaction. Using the nonlinear Schrödinger equation, we show that the phase fluctuations in the two-dimensional photon fluid obey the Klein–Gordon equation for a massless scalar field propagating in a curved spacetime. The results reveal that the photon fluid as well as the corresponding metric can be controlled by manipulating the system parameters. © 2017 Optical Society of America.
Publication Date: 2015
Journal of the Optical Society of America B: Optical Physics (07403224)32(8)pp. 1555-1563
We present and investigate an analogue model for controllable photon generation via the dynamical Casimir effect (DCE) in a cavity containing a degenerate optical parametric amplifier (OPA), which is pumped by an amplitude-modulated field. The time modulation of the pump field in the model OPA system is equivalent to a periodic modulation of the cavity length, which is responsible for the generation of the Casimir radiation. By taking into account the rapidly oscillating terms of the modulation frequency, the effects of the corresponding counter-rotating terms (CRTs) on the analogue Casimir radiation clearly emerge. We find that the mean number of generated photons and their quantum statistical properties exhibit oscillatory behaviors, which are controllable through the modulation frequency as an external control parameter. We also find that the time-modulated pumping may lead to the recently predicted phenomenon, the so-called "anti-DCE," in which pair photons can be coherently annihilated. We show that the Casimir radiation exhibits quadrature squeezing, photon bunching, and super-Poissonian statistics, which are controllable by modulation frequency. We also calculate the power spectrum of the intracavity light field. We find that the appearance of sidebands in the spectrum is due to the presence of the CRTs. © 2015 Optical Society of America.
Publication Date: 2013
Journal of Modern Optics (13623044)60(3)pp. 233-239
In this paper, to obtain an analogy between the curved spaces and the linear optics, we expand the idea of Sánchez-Soto and co-workers [Phys. Rep. 2012, 513, 191; Phys. Rev. A 2011, 84, 023830] to the multilayer films. We investigate effects of thickness and index of refraction of the films on the Lorentzian transformations. In addition, by using the multilayer films, we suggest a very simple experimental set-up which can serve as an analogue computer for testing special relativity. Finally, we draw an analogy between the Rindler space, as an example of the curved spaces, and a suitable multilayer film. Copyright © 2013 Taylor & Francis.
Publication Date: 2014
Applied Physics B: Lasers and Optics (09462171)116(3)pp. 521-531
We introduce the basics of an apodized 2f/1f wavelength modulation method for the spectroscopy of the R(9) transition line in the first overtone band of carbon monoxide (12C16O) in near-infrared (NIR) region around 2.33 μm. Performance of the method is investigated for high gas concentrations beyond the optically thin limit to generalize common 2f/1f wavelength modulation spectroscopy (WMS) reported by Rieker et al. (Appl Opt 48:5546, [28]). Numerical simulations are performed based on real experimental parameters associated with a NIR spectrometer designed in our laboratory. The results primarily show a more linear response and less error than occurred in the common WMS-2f/1f method for an optically thick sample. It is also theoretically shown that the apodized method enables sharpening the spectrum without peak displacement compared to the common WMS-2f/1f method. The validity of the method is verified experimentally by the trace detection of an air-broadened R(9) CO absorption line centered at 4,294.637 cm-1 at atmospheric pressure and room temperature. The effect of a so-called scaling k-factor on the sharpening of WMS-2f/1f signal is investigated through trace simulation and detection of CO and methane (CH4) lines in the scanning range of a distributed feedback laser. The obtained results show very good agreement between simulation and experiment. © 2013 Springer-Verlag Berlin Heidelberg.
Publication Date: 2012
Chinese Physics B (16741056)21(6)
A tunable continuous wave (cw) mid-infrared (MIR) laser based on difference-frequency generation (DFG) in a 1.5-cm long AgGaS 2 nonlinear crystal for trace gas detection is reported. Two visible and near-infrared diode lasers were used as pump and signal sources. The MIR-DFG laser was tunable in a wavelength range of 4.75 μm-4.88 μm. The phase-matching (PM) condition was non-critically achieved by adjusting the temperature of the crystal for fixed pairs of input pump and signal wavelengths. The required PM temperatures of the generated MIR-DFG wavelengths have been calculated by using three sets of recent Sellmeier equations and the temperature-dispersion equations of AgGaS 2 given by Willer U, et al. (Willer U, Blanke T and Schade W 2001 Appl. Opt. 40 5439). Then the calculated PM temperatures are compared with the experimental values. The performance of the MIR-DFG laser is shown by the trace detection of the P(16) carbon monoxide ( 12C 16O) absorption line in a laboratory-fabricated absorption cell. The enhanced sensitivity of about 0.6×10 -4 was obtained through the long path absorption provided by consecutive reflections between coated cylindrical mirrors of a constructed cell. © 2012 Chinese Physical Society and IOP Publishing Ltd.
Publication Date: 2016
Journal of the Chinese Chemical Society (00094536)63(10)pp. 886-892
An organic light-emitting diode was fabricated using cadmium selenide (CdSe)/poly(N-vinylcarbazole) nanocomposite as the hole transport layer (HTL). The CdSe nanoparticles (NPs) with a mean crystallite size of 6.2 nm were prepared by high-energy ball milling. Based on the current–voltage curves, the threshold voltage (V th) of the composite diode was found to be ~1.3 ± 0.1 V lower than that of the diode without CdSe, with a significant increase in the current density for the composite diode. Moreover, the electroluminescence (EL) properties (luminous flux, emittance, and intensity) of the diode were found to be enhanced by ~16% with respect to those of the diode without CdSe. The decrease of the threshold voltage and the increase of the current density and the EL were due to the CdSe NPs that operate as hole trap centers in the HTL. © 2016 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Publication Date: 2013
Optical and Quantum Electronics (discontinued) (03068919)45(1)pp. 67-77
We introduced a procedure of using local density of states for increasing the quality factor and Purcell factor of photonic crystal cavities. We used multipole expansion method for accurate calculation of local density of photonic states, stationary field profile, Q-factor, mode volume and Purcell factor of photonic crystal cavities. We found out that the quality factor exponentially increases with the number of additional photonic crystal layers around the cavity while the mode frequencies stay unchanged. We also demonstrated the method in studying the defect mode's behavior in photonic crystal cavities and showed that high Q-factor, small mode volume and high Purcell factor could be obtained with optimization of geometrical parameters of first neighboring layer. © 2012 Springer Science+Business Media, LLC.
Publication Date: 2016
Optics Letters (01469592)41(17)pp. 4087-4090
We numerically demonstrate a novel method to simultaneously reconstruct two unknown interfering wavefronts. The speckle-based phase retrieval technique is applied to derive the interference field. The derived interference field along with the phase-shifting concept is used for calculating the interfering wavefronts. Our results show the success of this method even under noisy conditions. © 2016 Optical Society of America.
Publication Date: 2014
Applied Optics (21553165)53(35)pp. 8295-8301
We investigate the determination of nonlinear refractive index n2, based on solving the transport of intensity equation (TIE) in conjunction with a pump-probe technique. As the pump and probe beams propagate through a sample, the pump-induced refractive index variations in the sample change the phase distribution of the probe beam. Using two recorded probe intensities in TIE, this phase change is derived, and so the nonlinear refractive index n2 is obtained. The influence of some characteristics of the pump beam and noise on the accuracy of determining n2 is also investigated. The simulation results show that the proposed method has a good capability for determining the nonlinear refractive index of materials. © 2014 Optical Society of America.
Publication Date: 2004
Journal of Modern Optics (13623044)51(13)pp. 1963-1982
A method for astigmatism calculations along any skew ray is presented. This is useful in the case of extremely wide angle optical systems (and not only imaging systems), where skew ray aberrations are most dominant, but it is essential in the case of systems which are not rotationally symmetric, where all the rays may be skew. Equations relating the position of the astigmatic foci before and after refraction or reflection are derived from the analysis of infinitesimal wave fronts in the immediate neighbourhood of the point of incidence of any ray, but particularly the central ray of any pencil on an optical surface. The method is then illustrated and checked with representative numerical examples. © 2004 Taylor & Francis Group, LLC.
