Publication Date: 2022
Optics Continuum (27700208)1(11)pp. 2347-2359
In the presence of high-strength turbulence, it is difficult to recognize close stars in ground-based imaging systems. Although adaptive optics could be helpful to reconstruct such images, there are always some remaining uncorrected phases for different turbulence conditions that could affect the recognition of close stars. Considering this, we have introduced a classification-based method by using a deep learning network to distinguish such star systems without correcting the wavefronts. To this aim, we have configured a Convolutional Neural Network (CNN). Five turbulence models are used to generate a dataset that includes thousands of images. Moreover, four metrics have been utilized to evaluate the CNN after the learning process. The accuracy of the network was upper than 80% for all of the turbulence models. The comparison of the five turbulence models is presented in detail, based on these metrics, and the robustness of the deep learning network is reported. © 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement.
Publication Date: 2022
Optik (00304026)249
The main idea of this work is to design a notch filter structure with a narrow notch width and maximum reflection while reducing fabrication challenges. In addition, using anti-reflection layers in the outermost part of the designed structure, the pass-band ripples are reduced. In this study, we considered [(nHnL)s (mHmL)p (nHnL)z] structure with n=5 and m=3. Using this form of design and combining 3 and 5 quarter-wave coefficients instead of 1 and 3, we could reach a narrower NW in fewer periods of HL layers. The stability of the deposition conditions and the density of the layers affect their quality and consequently the result of environmental tests. Hence, to construct the designed structure, we employed the sputtering method with RF and DC sources. In our experiments, we showed that the use of a simple shield prevents the oxidation of targets’ surfaces as well as reduces the deposition rate and increases the stability of deposition processes. Fabricated Samples have been subjected to a variety of environmental tests, including humidity, hard and soft abrasion, temperature, and adhesion tests with satisfactory results. © 2021
Publication Date: 2021
Optical Materials (09253467)117
Organic light-emitting diodes based on multiple-quantum-well (MQW) structures consisting of regular placement of N, N′-Di (1-naphthyl)-N, N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) and bathocuproine (BCP) layers have been fabricated. The findings show that the QWs structure can intensely raise the quality of OLED results. Compared with conventional device performance without MQW structure, the external quantum efficiency, current efficiency, and luminance of the OLED with two periods of QWs have been severely increased up to 1.77%, 25.40 cd/A, and 8686 cd/m2, respectively. These improvements in results are attributed to the enhanced hole-electron balance, owing to utilizing the MQW structure. © 2021 Elsevier B.V.
Publication Date: 2021
Optical Materials (09253467)114
Thin films have many applications in the field of optics and photonics. One of these applications is the fabrication of high-reflection mirrors for high-power lasers. High-power lasers also require mirrors with high laser induced damage threshold (LIDT). In this research, firstly, considering the principles of simulation, we have tried to design two types of mirrors, all-dielectric and metal-dielectric. Therefore, they are suitable in terms of both the reflectance spectrum and LIDT at 10.6 μm. To simulate and fabricate these two types of mirrors, ZnSe and Ge have been used as substrates and for thin film layers, Ge and ZnS have been used. In metal-dielectric mirrors, gold layers have also been used on the substrate as the metal layers. After design and simulation, the process of mirrors' fabrication was done by electron beam evaporation technique and the reflectance spectrum of the samples was taken, which shows the reflectance of all-dielectric mirrors is more than 99% and that of Metal-dielectric mirrors is more than 99.9%. Finally, measuring the LIDT of these two types of mirrors was performed based on ISO21254-1 2011 standard which shows that the metal-dielectric mirror with ZnSe substrate is the most suitable mirror for continuous lasers at 10.6 μm. © 2021 Elsevier B.V.
Publication Date: 2020
Solar Energy (0038092X)207pp. 409-418
Metallic nanoshells have attracted more attention compared to their solid counterparts as a result of producing high-yield plasmonic effects, such as large scattering and absorption cross-sections, potent near-field, strong optical trapping and long fluorescence time, during the plasmon hybridization mechanism. However, no focused study has been performed on optimizing this type of nanoparticles to improve the performance of polymer solar cells (PSCs) because they are difficult to synthesize. Our coupled optical-electrical simulation results show that the effort to fabricate may be worth it. In this work, we propose SiO2@Ag@SiO2 nanoparticles and optimize their size, material, and shells thickness. We show that their optimization makes full use of plasmonic effects possible, providing the PSCs with improvements in light concentration and optical absorption. Subsequently, we investigate the effect of nanoparticles’ concentration, their array and shape on the performance of PSCs based on PTB7:PC71BM, P3HT:PC60BM and PCDTBT:PC70BM. For the first time, we show that spherical nanoparticles can more improve the performance of PSCs compared to cubic ones, despite the fact that cubic nanoparticles have better plasmonic properties than their spherical counterparts. The results show significant improvement in electrical performance of the PSCs which results in efficiency enhancement of ~63%, ~106% and ~55%, respectively. © 2020 International Solar Energy Society
Publication Date: 2020
Proceedings of SPIE - The International Society for Optical Engineering (1996756X)11460
High damage threshold mirrors are necessary in high power laser systems. Different factors influence the rate of laser damage of these types of mirrors. In this research, the first thing that we tried was to simulate mirrors that are suitable for the reflectance spectra and are also in possession of high theoretically laser damage threshold at 10600 nm. After the task of simulation, the fabrication and coating process was performed by physical evaporation and in order to check the reflectance of the samples, their reflectance spectra were taken by uv-visible spectroscopy and their reflectance at 10600 nm is more than 99.5%. Finally, by measuring the thresholds of laser damage of mirrors made with continuous CO2 lasers, we came to the conclusion that the all-dielectric mirror with ZnS substrate has the highest laser induced damage threshold. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
Publication Date: 2019
Progress in Biomedical Optics and Imaging - Proceedings of SPIE (16057422)10878
Photoacoustic imaging modality is a new biomedical imaging which provides images with high resolution and contrast from different parts of body. In this paper, we have designed a new optical system by using a fiber bundle in order to imaging of a hemorrhage inside of the infant's head. We used Monte Carlo algorithm to simulate light propagation in the infant's head, an acoustic k-space method to simulate photoacoustic signal propagation in it, and time reversal image reconstruction algorithm to get 3D image of the hemorrhage. According to our simulation, this new optical system can provides homogeneous illumination on the infant's head Leads to more accurate images. Furthermore, we have designed and optimized an optical system in order to coupling light from laser source into a fiber bundle with more than 94% efficiency. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
Publication Date: 2018
Sensors and Actuators A: Physical (09244247)280pp. 47-51
Recently, organic-inorganic hybrid lead halide perovskite optical sensors have attracted lots of attention for their unique and remarkable optoelectronic properties like low-cost solution process deposition. Also, inorganic nanoparticles with narrow bandgap as photocarrier generator has been used in high efficiency low cost optical sensors to increase absorption spectrum. In this paper, we designed and fabricated a solution processed optical sensor by using nanocomposite of Methylammonium lead iodide and PbS nanoparticles as the active layer. It has high absorption in the broad range of spectrum that can work in small driving voltages (less than 1 V). It has low dark current and high photocurrent that are important parameters in optical sensors. This device achieves excellent photoresponsivity and high external quantum efficiency for broad range of wavelength from 370 nm to 940nm. © 2018 Elsevier B.V.
Publication Date: 2016
Optical Engineering (15602303)55(3)
We present a simple mathematical method for phase shifting that overcomes some phase shift errors and limitations of commonly used methods. The method is used to generate a sequence of phase-shifted interferograms from a single interferogram. The generated interferograms are employed to reconstruct the wavefront aberrations, as an application. The approach yields results with only very small deviations compared to both simulated wavefront aberrations, including the first 25 Zernike polynomials (0.05%) and those measured with a Shack-Hartmann sensor (0.5%). © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE).
Publication Date: 2015
Applied Optics (21553165)54(15)pp. 4732-4739
Singularities are discontinuities in optical wavefronts that can be produced by turbulence effects. Since the presence of singularities in a wavefront severely degrades the adaptive optics correction performance, their detection is very important. The gradient of the wavefront phase, as measured by the Shack-Hartmann wavefront sensor in the presence of singularities, can be considered as the sum of the rotational and irrotational parts. The rotational part of the phase gradient originating from the phase singularities can be considered as a potential based on Helmholtz-Hodge decomposition. The potential at the singularities positions appears as peaks and valleys of the potential depending on the positive or negative charges of singularities. In this article, the detection of phase singularities based on the branch point potential (BPP) method is investigated. The irrotational part of the gradient produces a background potential where singularities positions appear as local extremum of the potential. With our method, the irrotational part of the gradient is eliminated and the value of peaks and valleys is increased. In addition, in this method, the potential value characterizes the optical singularities. Here, analytical and simulation results for the detection of general forms of the singularity are presented. Our simulations show the performance of singularities detection in noisy conditions. © 2015 Optical Society of America.
Publication Date: 2015
Superlattices and Microstructures (10963677)85pp. 294-304
Films of silver nanoparticles have optical properties that are useful for applications such as plasmonic light trapping in solar cells. We report on the simple fabrication of Ag nanoparticle films via thermal evaporation, with and without subsequent annealing. These films result in a random array of particles of various shapes and sizes. The modeling of such a vast collection of particles is still beyond reach of the modern computers. We show that it is possible to represent the silver island films by the Bergman effective mediums with the same optical properties. The effective medium method provides us with deep insight about the shape, the size and the distribution of nanoparticles. The far field simulations of solar cells, in which the silver island film is replaced with an effective medium layer, show a reduction in the absorption of active layer. Besides, the near field simulations based on finite-difference time-domain technique demonstrate that the near field effects on active layer absorption are negligible and this method highlights the importance of nanoparticles shapes. The PCPDTBT:PCBM solar cells with embedded silver island films are fabricated, and it is found that their performances show the similar trend. This insight can be used for the optical analysis of thermally evaporated Ag nanoparticle films for the improvement of organic solar cells. © 2015 Elsevier Ltd. All rights reserved.
Publication Date: 2015
Physica Status Solidi - Rapid Research Letters (18626254)9(3)pp. 161-165
We report on the simple fabrication of Ag NP films via thermal evaporation and subsequent annealing. The NPs are formed on indium tin oxide electrodes, coated with PEDOT:PSS and implemented into PCPDTBT:PC70BM solar cells. Scanning electron microscopy and atomic force microscopy are used to determine the size distributions and surface coverage of the NP film. We apply finite-difference time-domain techniques to model the optical properties of different nanoparticle films and compare this with the absorption properties of the organic active layer. The simulations demonstrate that the absorption and scattering efficiency of the particles are very sensitive to particle geometry. Solar cells prepared with window electrodes containing NP layers with less surface coverage, show a 14.8% improvement in efficiency. We discuss variations in the external quantum efficiency of the devices in terms of forward scattering and parasitic absorption losses induced by the NP layer. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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: 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: 2014
Applied Optics (21553165)(7)pp. 1442-1448
The atmospheric turbulence measurement has received much attention in various fields due to its effects on wave propagation. One of the interesting parameters for characterization of the atmospheric turbulence is the Fried parameter or the atmospheric correlation length. We numerically investigate the feasibility of estimating the Fried parameter using a simple and low-cost system based on the stochastic parallel gradient descent (SPGD) algorithm without the need for wavefront sensing. We simulate the atmospheric turbulence using Zernike polynomials and employ a wavefront sensor-less adaptive optics system based on the SPGD algorithm and report the estimated Fried parameter after compensating for atmospheric-turbulence-induced phase distortions. Several simulations for different atmospheric turbulence strengths are presented to validate the proposed method. © 2014 Optical Society of America.
Publication Date: 2014
Optics Letters (01469592)39(6)pp. 1505-1508
We numerically and experimentally demonstrate an iterative method to simultaneously reconstruct two unknown interfering wavefronts. A three-dimensional interference pattern is analyzed and then Zernike polynomials and the stochastic parallel gradient descent algorithm are used to expand and calculate wavefronts. © 2014 Optical Society of America.
Publication Date: 2013
Thin Solid Films (00406090)539pp. 222-225
In this paper, a ZnS/Ag/ZnS/Ag/ZnS (ZAZAZ) nano-multilayer structure is designed to obtain high transmission in the visible range and low sheet resistance. The main parameters of the design are thicknesses of the layers. The optimum thickness of ZnS and Ag layers are calculated to be 30 and 12 nm, respectively. Nanostructure thin films of ZAZAZ with the optimized structure were deposited on a glass substrate by thermal evaporation method at room temperature. Also, the samples were annealed in air at different temperatures from 100 to 400 °C in steps of 100°C for an hour to investigate the effects of annealing treatment on structural, electrical and optical properties of samples. Sheet resistance of the multilayer film decreased initially with an increase of annealing temperature and increased further with an increase of annealing temperature beyond 300°C. High-quality multilayer films with a sheet resistance of 2.6 ω/sq and the maximum optical transmittance of 77.86% at 100 °C annealing temperature are obtained. The performance of the multilayer film was evaluated using a figure of merit. The observed property of the multilayer film is suitable for the application of transparent conductive electrodes. © 2013 Elsevier B.V. All rights reserved.
Publication Date: 2013
Physica E: Low-Dimensional Systems and Nanostructures (13869477)47pp. 303-308
In this paper, a ZnS/Ag/MoO3 (ZAM) nano-multilayer structure is designed theoretically and optimum thicknesses of each layer are calculated. ZnS/Ag/MoO3 multilayer films with optimized thicknesses have also been fabricated on glass substrates by thermal evaporation method at room temperature. The structural, electrical and optical properties of ZnS/Ag/MoO3 multilayer are investigated with respect to the variation of annealing temperature. X-ray diffraction patterns show that increase in annealing temperature increases the crystallinity of the structures. High-quality multilayer films with the sheet resistance of 4.5 Ω/sq and the maximum optical transmittance of 85% at 100 1C annealing temperature are obtained. The allowed direct band gap for annealing at different temperatures is estimated to be in the range of 3.37-3.79 eV. The performance of the ZAM multilayer films are evaluated using a predefined figure of merit. These multilayer films can be used as transparent conductive electrodes in optoelectronic devices such as solar cells and organic light emitting diodes. © 2012 Elsevier B.V.
Publication Date: 2013
Applied Optics (21553165)52(4)pp. 780-785
In this paper, design and simulation of conductive nanometric multilayer systems are discussed and optimum thickness of Ag and ZnS layers are calculated to reach simultaneously to high transmittance and low sheet resistance. The conductive transparent ZnS/Ag/ZnS/Ag/ZnS (ZAZAZ) nanometric multilayer systems are deposited on glass substrates at room temperature by a thermal evaporation method. The electrical, optical, and structural properties of these multilayers, such as sheet resistance, optical transmittance, and the root-mean-square surface roughness are obtained. High quality nanometric multilayer systems with sheet resistance of 2.7 Ω/sq and the optical transmittance of ∼75.5% are obtained for the ZAZAZ system. Organic light emitting diodes (OLEDs) were fabricated and tested on the ZAZAZ anode. The ZAZAZ multilayer anode based OLED shows the performance comparable to that of the indium-tin oxide anode based OLED.. © 2013 Optical Society of America.
Publication Date: 2012
Optics and Laser Technology (00303992)44(3)pp. 522-527
In this paper, we report the experimental results of a pulsed flash lamp Nd:YAG laser at wavelength of 1064 nm and Q-switched by Cr4:YAG solid state saturable absorber. We have obtained the output energy (E) and pulse- width (τp) of this laser for various initial transmissions of this saturable absorber. Furthermore, the effect of reflectivity of the output coupler (R), diameter of the rod (d), and optical length of the cavity (l) on this laser output data have been investigated. We have used the corner cube as a back mirror, which shows high laser stability and better brightness. We have obtained pulse-width 15 ns with 31 mJ output energy. We have also analyzed this laser theoretically and analytically, which agrees well with our corresponding experimental results. © 2011 Elsevier Ltd. All rights reserved.
Publication Date: 2007
Journal of Modern Optics (13623044)54(12)pp. 1779-1791
The different methods of optical systems' optimization such as Newton and least squares along with their modifications are reviewed. The Monte Carlo technique, as a statistical method which can overcome the shortcomings of these classic methods (such as the rate of convergence, the possibility of finding the overall minimum and avoiding local minima), is presented and compared with the others. A numerical example is presented to verify the method.
Publication Date: 2005
European Physical Journal B (14346028)44(1)pp. 63-70
An oscillator chain with dynamical traps and additive white noise is considered. Its dynamics are studied numerically. New type nonequilibrium phase transitions are shown to arise in the case when the trap effect is pronounced. Locally they manifest themselves in distortion of the symmetry of particle arrangement. Depending on the system parameters, the particle arrangement is characterized by the corresponding distributions taking either a bimodal form, or a twoscale one, or a unimodal onescale form that, however, deviates substantially from the Gaussian distribution. The particle velocities also exhibit a number of anomalies, in particular, their distribution can be extremely wide or take a quasi-cusp form. A large number of various cooperative structures and superstructures are found in the visualized time patterns. In a certain sense their evolution is independent of the individual particle dynamics, enabling us to regard them as dynamical phases. © EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005.
A new type of noised-induced phase transitions that should occur in systems of elements with motivated behavior is considered. By way of an example, a simple oscillatory system {x, ν = ẋ} with additive white noise is analyzed numerically. A chain of such oscillators is also studied in brief.
Publication Date: 2003
European Physical Journal B (14346028)36(1)pp. 115-118
A new type of noised induced phase transitions is proposed. It occurs in noisy systems with dynamical traps. Dynamical traps are regions in the phase space where the regular "forces" are depressed substantially. By way of an example, a simple oscillatory system {x,v = x} with additive white noise is considered and its dynamics is analyzed numerically. The dynamical trap region is assumed to be located near the x-axis where the "velocity" v of the system becomes sufficiently low. The meaning of this assumption is discussed. The observed phase transition is caused by the asymmetry in the residence time distribution in the vicinity of zero value "velocity". This asymmetry is due to a cooperative effect of the random Langevin "force" in the trap region and the regular "force" not changing the direction of action when crossing the trap region. © EDP Sciences, Società Italiana di Fisica, and Springer-Verlag 2003.
