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International Journal of Systems Science (00207721) 56(8)pp. 1726-1741
Piezoelectric deformable mirrors are complex systems with a reflective face-sheet and underlying actuators. The inherent hysteresis phenomenon in piezoelectric materials introduces nonlinearity and delay, rendering conventional control methods inappropriate for deformable mirror actuation. This study presents a disturbance observer-based controller with the generalised Bouc–Wen hysteresis parameter identification algorithm. Analytical proofs establish fixed-time stability for the observer and controller. A key feature of the proposed disturbance observer is the convergence of the estimated hysteresis to the actual value after a prescribed settling time, which facilitates precise hysteresis parameter identification. This is based on a data clustering technique, unlike most previous works. The proposed controller has the capability of hysteresis compensation and reference tracking in the piezoelectric deformable mirror actuators. Numerical simulation results are present to evaluate the tracking performance of the controller in the presence of random wavefront, the convergence of disturbance to the actual value in the fixed time, and identification of hysteresis parameters. © 2024 Informa UK Limited, trading as Taylor & Francis Group.
Chemical Methodologies (26457776) 9(11)pp. 1031-1040
The development of antibacterial textiles is essential for applications in healthcare, hygiene, and protective clothing. Among various approaches, Copper oxide nanoparticles (CuO NPs) were successfully deposited onto cotton fibres using an ultrasonic spray-coating technique to enhance their antibacterial functionality. The molarity of the precursor solution was identified as a critical factor influencing the morphology, structural properties, and antibacterial efficacy of the coated cotton fibres. Two molar concentrations (0.03 M and 0.06 M) were used to assess the effect of CuO loading on the coating characteristics and antibacterial performance. The treated fabrics were rigorously evaluated against two bacterial strains: Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). Comprehensive morphological and structural characterization of the CuO films was conducted using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) to determine surface uniformity, particle distribution, and crystallinity of the deposited thin films. The biological findings revealed that the CuO-coated fabrics exhibited significant antibacterial activity against both bacterial strains with increased effectiveness observed at the higher molarity. These findings indicate that ultrasonic deposition of CuO thin films on cotton fibres provides a promising route for producing antimicrobial textiles with potential applications in medical, hygienic, and protective clothing. Overall, CuO-coated cotton fabrics demonstrated effective bacterial inhibition, highlighting their potential for antimicrobial textile applications. The molarity of the CuO solution significantly influences both coating quality and antibacterial efficacy. © 2025 by Sami Publishing Company This is an open access article under the CC BY license.
Optics Express (10944087) 31(11)pp. 17250-17267
Piezoelectric deformable mirrors (DM) are benefited from the high accuracy and swift dynamics. The hysteresis phenomenon, which inherently exists in piezoelectric materials, degrades the capability and precision of the adaptive optics (AO) systems. Also, the dynamics of piezoelectric DMs make the controller design more complicated. This research aims to design a fixed-time observer-based tracking controller (FTOTC), which estimates the dynamics, compensates the hysteresis, and ensures tracking to the actuator displacement reference, in the fixed time. Unlike the existing inverse hysteresis operator-based methods, the proposed observer-based controller overcomes the computational burdens and estimates the hysteresis in real-time. The proposed controller tracks the reference displacements, while the tracking error converges in the fixed time. The stability proof is presented by two consecutive theorems. Numerical simulations demonstrate superior tracking and hysteresis compensation by the presented method, from a comparison viewpoint. © 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement.
Optics Continuum (27700208) 2(3)pp. 632-645
The turbulent atmosphere usually degrades the quality of images taken on Earth. Random variations of the refractive index of light cause distortion of wavefronts propagating to ground-based telescopes. Compensating these distortions is usually accomplished by adaptive optics (AO) approaches. The control unit of AO adjusts the phase corrector, such as deformable mirrors, based on the incoming turbulent wavefront. This can be done by different algorithms. Usually, these algorithms encounter real-time wavefront compensation challenges. Although many studies have been conducted to overcome these issues, we have proposed a method, based on the convolutional neural network (CNN) as a branch of deep learning (DL) for sensor-less AO. To this objective, thousands of wavefronts, their Zernike coefficients, and corresponding intensity patterns in diverse conditions of turbulence are generated and fed into the CNN to predict the wavefront of new intensity patterns. The predictions are done for considering the different number of Zernike terms, and the optimum number is achieved by comparing wavefront errors. © 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement.
Advanced Theory and Simulations (25130390) 5(2)
Computational screening is highly fruitful for initial studies of unknown molecules due to the capability of this tool in molecular discovery and the continuous improvement of computational methods. This article reports how computational studies on more than 300 organic molecules can identify thermally activated delayed fluorescent (TADF) emitters that emit light within the range of red up to near-infrared (NIR) with high TADF rates. According to time-dependent density functional theory (TD-DFT) computations, the best compounds exhibit a low singlet-triplet energy gap of 0.03 eV and oscillator strength of 0.0425, leading to a high rate of delayed fluorescence decay of 1.4483 μs−1. Additionally, an experimental-theory calibration approach is used as an adjunct to experimental research in the future, and emission wavelengths in promising charge-transfer compounds are estimated as large as 689 nm. © 2021 Wiley-VCH GmbH
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.
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
Isfahan, S.P. ,
Fallah, H. ,
Safari, R. ,
Zabolian, H. ,
Rezaei, S. ,
Moghadam, M. Surfaces and Interfaces (24680230) 29
The atomic electronic properties of two Schiff base Pt-salophen structures, with H and Br substitution atoms are studied using DFT/TDDFT computational calculation methods. Also, based on the quantum atoms-in-molecules theory (QTAIM), the atomic basin properties of these molecular systems are investigated. QTAIM analysis results show that these molecules can be grouped into donor-like and acceptor-like sections. Intra-molecular charge and thus energy transfer efficiency for each molecular systems are also studied, using the local contour map of the atomic electronic densities. In addition, these two structures have been synthesized and the absorption property of the molecular structures have been investigated. Finally, using these Schiff base Pt-salophen complexes (as an emitter layer), two different types of organic light emitting devices (OLEDs) have been fabricated. This study's results show that there is a good agreement between the theoretical analysis derived via QTAIM analysis and the experimental results of the fabricated devices. These results provide a new approach of the QTAIM analysis to be applied in investigation of organic materials used in OLED optoelectronic devices. © 2022 Elsevier B.V.
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.
Halaney, D.L. ,
Katta, N. ,
Fallah, H. ,
Aguilar, G. ,
Milner, T.E. Frontiers in Bioengineering and Biotechnology (22964185) 9
Transparent “Window to the Brain” (WttB) cranial implants made from a biocompatible ceramic, nanocrystalline Yttria-Stabilized Zirconia (nc-YSZ), were recently reported. These reports demonstrated chronic brain imaging across the implants in mice using optical coherence tomography (OCT) and laser speckle imaging. However, optical properties of these transparent cranial implants are neither completely characterized nor completely understood. In this study, we measure optical properties of the implant using a swept source OCT system with a spectral range of 136 nm centered at 1,300 nm to characterize the group refractive index of the nc-YSZ window, over a narrow range of temperatures at which the implant may be used during imaging or therapy (20–43°C). Group refractive index was found to be 2.1–2.2 for OCT imaging over this temperature range. Chromatic dispersion for this spectral range was observed to vary over the sample, sometimes flipping signs between normal and anomalous dispersion. These properties of nc-YSZ should be considered when designing optical systems and procedures that propagate light through the window, and when interpreting OCT brain images acquired across the window. © Copyright © 2021 Halaney, Katta, Fallah, Aguilar and Milner.
Scientific Reports (20452322) 11(1)
The solution processable polymer solar cells have shown a great promise as a cost-effective photovoltaic technology. Here, the effect of carrier mobility changes has been comprehensively investigated on the performance of P3HT:PCBM polymer solar cells using electro-optical coupled simulation regimes, which may result from the embedding of SiO2@Ag@SiO2 plasmonic nanoparticles (NPs) in the active layer. Firstly, the active layer thickness, stemmed from the low mobility of the charge carriers, is optimized. The device with 80 nm thick active layer provided maximum power conversion efficiency (PCE) of 3.47%. Subsequently, the PCE has increased to 6.75% and 6.5%, respectively, along with the benefit of light scattering, near-fields and interparticle hotspots produced by embedded spherical and cubic nanoparticles. The PCE of the devices with incorporated plasmonic nanoparticles are remarkably enhanced up to 7.61% (for spherical NPs) and 7.35% (for cubic NPs) owing to the increase of the electron and hole mobilities to μe=8×10-7m2/V/s and μh=4×10-7m2/V/s, respectively (in the optimum case). Furthermore, SiO2@Ag@SiO2 NPs have been successfully synthesized by introducing and utilizing a simple and eco-friendly approach based on electroless pre-treatment deposition and Stober methods. Our findings represent a new facile approach in the fabrication of novel plasmonic NPs for efficient polymer solar cells. © 2021, The Author(s).
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.
EPJ Applied Physics (12860042) 96(3)
In digital holography, errors of the reference field degrade the quality of the reconstructed object field. In this paper, we propose an effective method in phase-shifting digital holography in which the reference field does not need to be known and perfect. The unknown complex amplitudes of both reference and object fields are derived simultaneously. The method employs only five digital holograms and a single execution of a phase retrieval algorithm. So, the required measurements and algorithm executions in this method are fewer than those in other methods; it suggests a simpler and faster method. The effectiveness of the suggested method is indicated by simulation, under noise-free and noisy conditions. Moreover, the capability of the method to extract full information about the phase singularities in both fields is demonstrated. © EDP Sciences 2021.
Scientific Reports (20452322) 11(1)
In this study, the effect of the plasmon hybridization mechanism on the performance and refractive index (RI) sensitivity of nanoshell, nanocage and nanoframe structures is investigated using the finite-difference time-domain simulation. To create nanocage structure, we textured the cubic nanoshell surfaces and examined the impact of its key parameters (such as array of cavities, size of cavities and wall thickness) on the nanocage's RI-sensitivity. Synthesis of the designed nanocages is a challenging process in practice, but here the goal is to understand the physics lied behind it and try to answer the question “Why nanoframes are more sensitive than nanocages?”. Our obtained results show that the RI-sensitivity of nanocage structures increases continuously by decreasing the array of cavities. Transforming the nanocage to the nanoframe structure by reducing the array of cavities to a single cavity significantly increases the RI-sensitivity of the nanostructure. This phenomenon can be related to the simultaneous presence of symmetric and asymmetric plasmon oscillations in the nanocage structure and low restoring force of nanoframe compared to nanocage. As the optimized case shows, the proposed single nanoframe with aspect ratio (wall length/wall thickness) of 12.5 shows RI-sensitivity of 1460 nm/RIU, the sensitivity of which is ~ 5.5 times more than its solid counterpart. © 2021, The Author(s).
Applied Optics (21553165) 59(33)pp. 10618-10625
We present a simple and robust technique for measuring the nonlinear refractive index. The principle is based on an iterative phase retrieval algorithm with a pump–probe system. Different strong phase modulations are intentionally introduced into the probe beam, and corresponding diffraction intensity patterns are recorded. The recordings are used in the phase retrieval algorithm to reconstruct the pump-induced phase on the probe beam. The nonlinear refractive index is then extracted from the reconstructed phase. The reconstruction method offers a straightforward procedure and a simple lensless setup. Simulations validate the proposed method. The effects of different characteristics of the pump and probe beams on the quality of reconstructions are investigated. The obtained results demonstrate that the reconstructions are accurate even for the probe beams with complex-valued fields and non-Gaussian pump beams; it removes the requirement for smooth fields of the pump and probe beams. The validity of the method in noisy conditions is also shown. © 2020 Optical Society of America.
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
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.
Hassanpour behbahani, M. ,
Esfandiary, H. ,
Pakmanesh, M.R. ,
Mirjaffari, S.A. ,
Fallah, H. Journal of Electronic Materials (03615235) 49(9)pp. 5552-5560
In this study, using the physical vapor deposition (PVD) method by thermal evaporation technique, aluminum was deposited on a 13-μm polyethylene terephthalate (PET) substrate. A 150-nm-thick layer of aluminum was deposited on both sides of the substrate for use in thermal layers. The thermal properties, including the specific heat capacity, thermal conductivity coefficient, and thermal expansion coefficient, were measured by differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and xenon flash analysis (XFA), respectively. The electrical analyses were carried out to determine the breakdown voltage, volumetric resistance, and dielectric strength, and the results were analyzed. The electrical capacitance of the sample (sample is capacitive with dielectric PET) was obtained through simulation. The dielectric constant and the electrical resistance were calculated using the obtained values of the two parameters and compared with the measurement results. The Al-PET temperature glass (Tg) value was measured by TMA and DSC analyses. A comparison of the results shows that they are the same. © 2020, The Minerals, Metals & Materials Society.
Hassanpour behbahani, M. ,
Fallah, H. ,
Esfandiary, H. ,
Pakmanesh, M.R. ,
Mirjafari, S.A. Applied Physics A: Materials Science and Processing (14320630) 126(5)
In this study, we used the PVD method by thermal evaporation technique, in which aluminum deposited on a 13 microm polyethylene terephthalate substrate. The aluminum deposition was carried out in different thicknesses (100, 150, 200, 250, 300 nm) on both sides of the substrate and two different deposition rates (a high rate of 6 nm/s and a low rate of 0.4 nm/s). Absorptance and emittance analyses were done. These analyses were evaluated by ECSS-Q70-71A standard for use in thermal blankets. According to analyses and evaluation, it was found that the sample with a thickness of 150 nm has the optimum values of absorptance and emittance for use in the thermal layers. Surface morphologies of the samples with the thicknesses of 100, 150, 200, 250, and 300 nm were investigated using AFM analysis. Other structural properties of the Al-PET sample with a thickness of 150 nm were determined by structural analyses, including XRD, FTIR, and FESEM. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
Zabolian, H. ,
Fallah, H. ,
Rahimi, G. ,
Khashei, H. ,
Isfahan, S.P. Surfaces and Interfaces (24680230) 17
In this work, The influence of oblique ion bombardment treatment of the surface of indium tin oxide (ITO) thin films, on the surface parameters of the film and then the performance of organic light-emitting diodes (OLEDs) has been investigated. Both commercially available and uniquely fabricated ITO substrates which were deposited by electron beam evaporation method have been employed. The ITO surface characteristics have been investigated by atomic force microscopy (AFM), X ray diffraction (XRD) and UV-Vis-NIR spectrophotometer. Then a typical OLED device was fabricated on different ITO surfaces and characterized by Keitley 2450 and JAZ spectrometer. The results show that after anode surface treatment by means of oblique Argon ion bombardment method, surface roughness is extremely decreased, which resulted in increasing current and power efficiencies and also there was no evidence of ohmic junctions before driving voltage. The maximum ohmic resistance, current and power efficiencies were 371 MΩ, 6.4 cd/A and 0.91 cd/w, respectively. Also it is found that local non-emissive area or dark spots creation reduced for treated surface device. These findings provide a simple way to effectively reduce the roughness of the ITO films as anode to be applied in optoelectronic devices such as OLEDs. © 2019 Elsevier B.V.
Ranjbaran, S.M. ,
Kratkiewicz, K. ,
Manwar, R. ,
Fallah, H. ,
Hajimahmoodzadeh, M. ,
Nasiri avanaki, M.R. 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.
Journal of Optics (United Kingdom) (20408986) 21(7)
In this paper, a lenslet array is applied to simultaneously reconstruct the unknown phases of two interfering fields from intensity data. Recorded intensity patterns at the lenslet array plane and at the focal plane of the lenslet array are used in the stochastic parallel gradient descent algorithm for reconstruction. The lenslet array assures a fast-convergence and non-stagnating phase retrieval. Numerical simulations are presented to validate the proposed method. The obtained results show that the method permits a robust and accurate phase reconstruction and exhibits a high immunity to noise. © 2019 IOP Publishing Ltd.
Materials Research Express (20531591) 6(5)
The effect of second phase size (200, 400, 600 and 800 nm) and volume fraction (10, 20 and 30%) on light transmission behavior of ZnS/diamond composite was simulated using Mie theory and FDTD method. It is expected that the results of FDTD method to be close to experimental results. To validate this approach, simulation results of Mie theory and FDTD method were compared with experimental light transmission (T) of 88.7-11.3 vol% ZnS/diamond composite, reported previously by Xue and et al, and it is shown that results of FDTD method matched well with these experimental results. Because of considering particles interaction and the higher accuracy of the FDTD method in calculating the scattering cross section than the Mie theory, the difference between simulation curves of ZnS/diamond nanocomposite based on Mie theory and FDTD method became more significant with increasing second phase size particularly at greater volume fractions and at short wavelengths. Simulated light transmission curves obtained by FDTD method showed that the optimized second phase size should be smaller than 800 nm for volume fraction of 10% and smaller than 200 nm for volume fractions of 20 and 30%. On the other words, within these sizes, the reduction of light transmission of ZnS/diamond composite compared to monolithic ZnS is lower than 10%. © 2019 IOP Publishing Ltd.
Solar Energy (0038092X) 163pp. 600-609
The local surface plasmon resonance (LSPR) effects of metallic nanoparticles (such as light scattering and giant local field) in organic materials can improve the optical absorption capability of organic solar cells. This is especially important for polymer solar cells where the active layer thickness has been limited (<150 nm) due to short electron-hole diffusion length. LSPR effects depend on the features of nanoparticle, such as shape and size. Qua cubic nanoparticle produces a stronger LSPR compared to other shapes and increased LSPR effect increases the light absorption. However, fabrication of the cubic nanoparticle is much more difficult compared to fabrication of spherical ones. This study aims to increase LSPR effects of spherical nanoparticles and we propose the SiO2@Au@SiO2 new structure for them. Our simulation results demonstrate increase in power absorption and short circuit current of ∼103% and ∼118%, respectively, with square array of SiO2@Au@SiO2 nanoparticles with central nanoparticle inserted in thin active layer compared to the structure without nanoparticles. Subsequently, we propose the new square array without central nanoparticle for SiO2@Au@SiO2 nanoparticles. Calculations show significant enhancement in power absorption and short circuit current of respectively ∼136% and ∼154%, compared to the structure without nanoparticles. These improvements are justified pursuant to enhanced light trapping inside the active layer. © 2018 Elsevier Ltd
Journal of the Optical Society of America B: Optical Physics (07403224) 35(12)pp. 3063-3068
We present a simple and robust method to simultaneously reconstruct two unknown interfering fields. First, the interference field (IF) is recovered from diffraction interference intensity recordings. The recovered IF along with a set of interference intensities generated by the phase shifting technique is used in an iterative phase retrieval algorithm to derive both the phase and amplitude information of the interfering fields. Numerical simulations are presented to validate the proposed method. In the simulation, we consider two arbitrary interfering fields with unrelated amplitudes and phases, creating a difficult problem where two complicated fields must be retrieved simultaneously. In addition, the phase of the second interfering field contains a vortex with a topological charge of 5. Under noise-free conditions, the relative errors of phases, defined as the root-mean-square (RMS) value of the residual phase divided by the RMS value of the original phase, for the first and second interfering fields are of the order of 10−5 and 10−6, respectively, where the relative error of amplitudes is of the order of 10−7. For 5% and 10% noise, the obtained relative error of phase is of the order of 10−2 for the first interfering field and 10−3 for the second interfering field, where the relative error of amplitudes is of the order of 10−2. These results show the success of the proposed method even under noisy conditions and in the presence of phase vortices. © 2018 Optical Society of America.
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.
Aray, A. ,
Saghafifar, H. ,
Fallah, H. ,
Soltanolkotabi, M. IEEE Sensors Journal (1530437X) 17(14)pp. 4466-4471
Surface plasmon resonance (SPR) has been a topic of intense research in refractive index sensors due to the benefits of high resolution, high sensitive, real-time, and label-free technology. But losses restrict the operational parameters of SPR-based devices. In this paper, a new design of SPR sensor structures using gain medium are proposed. These novel prisms-based structures are based on Otto and Kretschmann configurations. Regard to gain coefficient of an active layer, two different regimes have been introduced in which loss compensating and amplifying surface plasmons polaritons are occurred. The effect of geometrical parameters on SNR enhancement factor is investigated theoretically and finally, the optimum layers' thicknesses for the fixed values of gain coefficient and wavelength will be examined. Signal-to-noise ratio in the proposed structures could be enhanced by a factor of two orders of magnitudes. © 2001-2012 IEEE.
Applied Optics (21553165) 56(5)pp. 1358-1364
An iterative phase retrieval method is applied to a sequence of intensity patterns obtained from a Shack-Hartmann sensor to reconstruct an unknown wavefront. The simulation results validate the proposed technique even under noisy conditions. The effects of different parameters on the reconstruction accuracy are also investigated by a simulation. In addition, it is shown that this technique has a good capability for detecting the presence and location of optical vortices in the wavefront. The orientation and topological charge of the vortex are also reconstructed correctly. © 2017 Optical Society of America.
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
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.
Moradi, Z. ,
Jahanshah, F. ,
Fallah, H. ,
Haji mahmoodzade, M. ,
Sahraee, M. ,
Zabolian, H. Applied Physics B: Lasers and Optics (09462171) 122(8)
We designed and fabricated the transmission quarter-wave plate phase retarder at 1064 nm using optical nanometric thin films of silicon oxide and titanium oxide. Final design consists of 32 layers. Transmissions of polarizations are equal and ≥99 % and their phase difference is 90°. System consists of two 16 layers systems that coated with the same condition on BK7 glass substrates then attached together with optical glue. Electron beam evaporation method was used for depositing materials. Photo spectrometer was used for measuring transmission spectrum of system. Transmission of polarizations was ≥95 % and equal. A polarimeter was used for testing systems. Polarization of beam was circular. © 2016, Springer-Verlag Berlin Heidelberg.
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).
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.
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.
Sorayaie, P. ,
Yusefi, M. ,
Fallah, H. ,
Parsanasab, G. Applied Physics A: Materials Science and Processing (14320630) 118(2)pp. 519-524
In this paper, the growths of ZnO nano- and microstructures by VLS mechanism have been studied. A piece of silica fiber (SMF-28 optical fiber) was used as a substrate. By controlling the experimental conditions, nano- and microstructures of ZnO with different shapes and sizes were grown around the optical fiber, which can be used as an optical fiber sensor. A star-shaped ZnO microstructure was obtained in this research. Pyramidal structures were grown on each side of vertical hexagonal microrods which formed the seven-pointed star-shaped microstructures. This growth process was carried out in a special quartz container in a tube furnace at temperatures around 400–550 °C without any additional catalyst. XRD, SEM and PL spectroscopy were used for the characterization of the produced nanostructures. The influence of temperature, reactant and carrier gases flow rate on the morphology of ZnO nanostructure was investigated. © 2014, Springer-Verlag Berlin Heidelberg.
Polymer Bulletin (14362449) 72(11)pp. 2979-2990
A new copolymer was synthesized via reaction of new pyridine-containing dibromo compound, 2,6-bis(4-bromophenyl)-4-(naphthalen-1-yl) pyridine, with thiophene-based diboronic ester via Suzuki cross-coupling reactions. 2,6-Bis(4-bromophenyl)-4-(naphthalen-1-yl) pyridine was synthesized starting from condensation reactions of 4-bromoacetophenone and 1-naphthaldehyde. The synthesized monomer and polymer were characterized by FT-IR and NMR spectroscopy. The physical properties of the polymer, including solubility and viscosity were studied, and the results showed good solubility and chain growth for polymer. Maximum absorption peak for polymer was 388 nm. The optical band gap energy of the polymers was determined by absorption onset and found to be 2.38 eV for polymer. © 2015, Springer-Verlag Berlin Heidelberg.
Haidari, G. ,
Hajimahmoodzadeh, M. ,
Fallah, H. ,
Peukert, A. ,
Chanaewa, A. ,
Von hauff, E. 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.
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.
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.
Sahraee, M. ,
Fallah, H. ,
Moradi, Z. ,
Zabolian, H. ,
Mahmoodzade, M.H. European Physical Journal Plus (21905444) 129(12)pp. 1-6
In this paper a thin-film polarizer at a wavelength of 1540 nm was designed and fabricated. These types of polarizer are usually used in laser systems to obtain linearly polarized light beams. Our design consists of a system of eighteen dielectric thin-film layers from repeated pairs of titanium dioxide and silicon dioxide layers that are deposited on a BK7 glass substrate. Design was carried out based on theoretical principles and computer calculations. Thin-film design software was used for designing the polarizer. The angle of incidence was supposed to be 56° that is the Browster angle for BK7 glass. Performance and laser-induced damage threshold of the polarizer were enhanced by a suitable selection of various parameters including thickness of each layer, their number and the electric field distribution of layers. After several designs, fabrications and refinement of parameters, the final polarizer was designed. Then the final sample of the polarizer was prepared using the electron beam evaporation (EBE) technique with Balzers BAK 760 coating machine. Spectral transmittance of the sample was measured by Shimadzu 3100 UV-VIS-NIR spectrophotometer. Investigation of spectral transmittance showed that at a wavelength of 1540nm, the transmission of P polarization is 87.82 and the transmission of S polarization is 0.43 which show a ratio (TP/TS of 204. So, this ratio is an acceptable value for our desired polarizer. © 2014, Società Italiana di Fisica and Springer-Verlag Berlin Heidelberg.
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.
Ashrafi, F. ,
Feiz, S.M.H. ,
Fallah, H. ,
Yousefi, M.H. ,
Shivaee, M.H. Journal of Materials Science: Materials in Electronics (09574522) 25(4)pp. 1880-1886
In this paper, zinc selenide nanoparticles powder was successfully synthesized using rapid polyol method. The preparation method was changed by using new Se solvents in the final stage to delete seleniums which have not participated in reaction product. This change in the preparation method increased the purity of final product (92 %); and using selenium's solvents as detergents caused the production of ZnSe with roughly 100 % purity. X-ray diffractions showed that the samples had a cubic structure with lattice constant equalling 5.6699 Å and with 5.5 nm for crystallite size. Atomic force microscopy (AFM) and high resolution transmission electron microscopy (HRTEM) images showed that the particles were almost spherical and well crystallized ZnSe nanoparticles were formed. The average sizes of nanoparticles were 15 and 16.4 nm for AFM and HRTEM, respectively. Absorption Spectra of all samples showed a blue shift in comparison with bulk ZnSe. It showed low absorption in a wide range of wavelengths. Band gap energy of the pure ZnSe nanoparticles was found to be 4.51 eV, which is higher than that of the bulk value of ZnSe (2.67 eV). Photoluminescence spectra of the samples showed emission at 450-500 nm wavelengths at room temperature which are useful for the application of solar cells, quantum dot light-emitting diodes and blue organic light-emitting diodes devices. © 2014 Springer Science+Business Media New York.
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.
Designed Monomers and Polymers (15685551) 17(5)pp. 401-415
Two new copolymers, P1 and P2, composed of 4[4-(alkoxy)phenyl]-2, 6-bis(4-bromophenyl)pyridine and bithiophene units, have been synthesized via Suzuki cross-coupling reactions. 4[4-(alkoxy)phenyl]-2, 6-bis(4-bromophenyl)pyridines were synthesized starting from condensation reaction of 4-bromoacetophenone and 4-hydroxy benzaldehyde, and subsequent alkoxylation of hydroxyl groups. All of the polymers and intermediates were characterized using FTIR and NMR spectroscopies. The synthesized polymers exhibit good solubility in common organic solvents. The maximum absorption peak for P1 and P2 was 430 and 420 nm, respectively. The optical band gap energy of the polymers was determined by absorption onset and found to be 2.17 eV for P1 and 2.13 eV for P2. © 2013 Taylor & Francis.
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.
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.
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.
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.
Varnamkhasti, M.G. ,
Fallah, H. ,
Mostajabodaavati m., M. ,
Ghasemi, R. ,
Hassanzadeh, A. Solar Energy Materials and Solar Cells (09270248) 98pp. 379-384
In this work, small molecule organic photovoltaic cells based on copper phthalocyanine (CuPc)/C 60 hetrojunction were fabricated. To have a good band structure matching between the work function of the anode and the highest occupied molecular orbital of the organic material the introduction of a buffer layer is necessary. Efficiency of devices shows a strong improvement when the metal oxides such as molybdenum oxide (MoO 3) and tungsten oxide (WO 3) were used as buffer layer between the ITO anode and active layer. The effect of MoO 3 and WO 3 thickness on the performance of the photovoltaic devices was investigated and compared. The thickness of each buffer layer was optimized to have better hole transport. Also the devices performance was analyzed based on the surface roughness of bare ITO, and ITO, which covered with WO 3 and MoO 3. It was found that the anode buffer layer thickness is a very important factor in controlling the electrical characteristics of the organic photovoltaic devices. It is shown that the best results are obtained with a 4 nm MoO 3. © 2011 Elsevier B.V. All rights reserved.
Vacuum (0042207X) 86(7)pp. 871-875
Zinc oxide thin films have been grown on glass substrate at room temperature by electron beam evaporation and then were annealed in annealing pressure 600 mbar at different temperatures ranging from 250 to 550°C for 30 min. Electrical, optical and structural properties of thin films such as electrical resistivity, optical transmittance, band gap and grain size have been obtained as a function of annealing temperature. X-ray diffraction has shown that the maximum intensity peak corresponds to the (002) predominant orientation for ZnO films annealed at various temperatures. The full width at half maximum, decreases after annealing treatment which proves the crystal quality improvement. Scanning electron microscopy images show that the grain size becomes larger by increasing annealing temperature and this result agrees with the X-ray diffraction analysis. © 2011 Elsevier Ltd. All rights reserved.
Parsa, S. ,
Fallah, H. ,
Ramezani, M. ,
Soltanolkotabi, M. Applied Optics (21553165) 51(30)pp. 7339-7344
We studied the conditions for generating passive Bessel-Gauss beams by using an axicon. We designed an appropriate Gaussian resonator and extracted a quasi-fundamental Gaussian mode from a pulsed Nd:YAG laser pumped by a Xenon flash lamp and measured its parameters, such as propagation factor, divergence angle, and Rayleigh range. Then we generated passive Bessel-Gauss beams using an axicon and investigated their propagation properties, theoretically and experimentally. For example, for the axicon of 1°, the output energy and the Rayleigh range of the generated Bessel-Gauss beams were measured to be 58 mJ and 229.3 mm, respectively. We compared these properties with our results of the Gaussian mode. Finally, by using axicons with different apex angles, and also by changing the beam spot size on the axicon, we generated Bessel-Gauss beams and studied their properties theoretically and experimentally. © 2012 Optical Society of America.
Varnamkhasti, M.G. ,
Fallah, H. ,
Mostajabodaavati m., M. ,
Hassanzadeh, A. Vacuum (0042207X) 86(9)pp. 1318-1322
In this study, MoO 3/Ag/ITO/glass (MAI) nano-multilayer films were deposited by the thermal evaporation technique and then were annealed in air atmosphere at 200 °C for 1 h. The effects of Ag layer thickness on electrical, optical and structural properties of the MoO 3(45 nm)/Ag(5-20 nm)/ITO(45 nm)/glass nano-multilayer films were investigated. The sheet resistance decreased rapidly with increasing Ag thickness. Above a thickness of 10 nm, the sheet resistances became somewhat saturated to a value of 3(Ω/). The highest transparency over the visible wavelength region of spectrum (85%) was obtained for 10 nm Ag layer thickness. Carrier mobility, carrier concentrations, transmittance and reflectance of the layers were measured. The allowed direct band-gap for an Ag thickness range 5-20 nm was estimated to be in the range 3.58-3.71 eV. The XRD pattern showed that the films were polycrystalline. X-ray diffraction has shown that Ag layer has a (111) predominant orientation when deposited. The figure of merit was calculated for MAI multilayer films. It has been found that the Ag layer thickness is a very important factor in controlling the electrical and optical properties of MAI multilayer films. The optimum thickness of the Ag layer for these films was determined. The results exhibit that the MAI transparent electrode is a good structure for use as the anode of optoelectronic devices. © 2011 Elsevier Ltd. All rights reserved.
Journal of Nonlinear Optical Physics and Materials (17936624) 21(4)
The relation between position of optical source and excitation of photonic crystal cavity modes are investigated. For multimode cavities, the source position considerably affects the modes' excitation. The frequency distributions of local density of photonic states in a multimode cavity differ for source positions at structural symmetric locations and nonsymmetrical ones. It was also found that the geometry of cavity's neighboring layers has strong influence on the spatial and spectral distributions of modes. The results also show that the shifts of various cavity modes in frequency domain have different sensitivity with respect to geometrical tolerance. This can be used in various applications which need mode tuning. © World Scientific Publishing Company.
Optics Letters (01469592) 37(12)pp. 2226-2228
We present a new method for subjectively evaluating intraocular lenses (IOLs) without implantation surgery. To illustrate the method, three types of single-piece IOL (equispherical monofocal, rotational symmetric aspheric monofocal, and diffractive bifocal) were assembled into a model eye and evaluated using an ocular adaptive optics system by a single subject. To separate the spherical aberration of the crystalline lens, the subject's corneal topography and wavefront aberrations were measured and modeled. Three levels of Zernike spherical aberration were generated and superposed on the IOLs and the subject's eye. The corrected distance visual acuity was measured by psychophysical visual procedure. © 2012 Optical Society of America.
Zadsar, M. ,
Fallah, H. ,
Haji mahmoodzadeh, M. ,
Hassanzadeh, A. ,
Varnamkhasti, M.G. Materials Science in Semiconductor Processing (13698001) 15(4)pp. 432-437
Tin oxide (SnO 2) thin films were deposited on glass substrates by thermal evaporation at different substrate temperatures. Increasing substrate temperature (T s) from 250 to 450 °C reduced resistivity of SnO 2 thin films from 18×10 -4 to 4×10 -4 Ω cm. Further increase of temperature up to 550 °C had no effect on the resistivity. For films prepared at 450 °C, high transparency (91.5%) over the visible wavelength region of spectrum was obtained. Refractive index and porosity of the layers were also calculated. A direct band gap at different substrate temperatures is in the range of 3.55-3.77 eV. X-ray diffraction (XRD) results suggested that all films were amorphous in structure at lower substrate temperatures, while crystalline SnO 2 films were obtained at higher temperatures. Scanning electron microscopy images showed that the grain size and crystallinity of films depend on the substrate temperature. SnO 2 films prepared at 550 °C have a very smooth surface with an RMS roughness of 0.38 nm. © 2012 Elsevier Ltd. All rights reserved.
Zadsar, M. ,
Fallah, H. ,
Haji mahmoodzadeh, M. ,
Tabatabaei, S.V. Journal of Luminescence (00222313) 132(4)pp. 992-997
Transparent conductive WO 3/Ag/MoO 3 (WAM) multilayer electrodes were fabricated by thermal evaporation and the effects of Ag layer thickness on the optoelectronic and structural properties of multilayer electrode as anode in organic light emitting diodes (OLEDs) were investigated using different analytical methods. For Ag layers with thickness varying between 5 and 20 nm, the best WAM performances, high optical transmittance (81.7%, at around 550 nm), and low electrical sheet resistance (9.75 Ω/cm 2) were obtained for 15 nm thickness. Also, the WAM structure with 15 nm of Ag layer thickness has a very smooth surface with an RMS roughness of 0.37 nm, which is suitable for use as transparent conductive anode in OLEDs. The current density-voltage-luminance (J-V-L) characteristics measurement shows that the current density of WAM/PEDOT:PSS/TPD/Alq 3/LiF/Al organic diode increases with the increase in thickness of Ag and WO 3/Ag (15 nm)/MoO 3 device exhibits a higher luminance intensity at lower voltage than ITO/PEDOT:PSS/TPD/Alq 3/LiF/Al control device. Furthermore, this device shows the highest power efficiency (0.31 lm/W) and current efficiency (1.2 cd/A) at the current density of 20 mA/cm 2, which is improved 58% and 41% compared with those of the ITO-based device, respectively. The lifetime of the WO 3/Ag (15 nm)/MoO 3 device was measured to be 50 h at an initial luminance of 50 cd/m 2, which is five times longer than 10 h for ITO-based device. © 2011 Elsevier B.V. All rights reserved.
Parsa, S. ,
Fallah, H. ,
Ramezani, M. ,
Soltanolkotabi, M. Applied Optics (21553165) 51(31)pp. 7475-7481
Nondiffracting Bessel–Gauss beams are assumed as the superposition of infinite numbers of Gaussian beams whose wave vectors lie on a cone. Based on such a description, different methods are suggested to generate these fields. In this paper, we followed an active scheme to generate these beams. By introducing an axicon–based resonator, we designed the appropriate resonator, studied its resonance modes, and analyzed the beam propagation outside the resonator. Experimentally, we succeeded to obtain Bessel–Gauss beams of the first kind and zero order. We also investigated the changes in effective parameters on the output beam, both theoretically and experimentally. © 2012 Optical Society of America.
Keshavarzi, R. ,
Mirkhani, V. ,
Moghadam, M. ,
Tangestaninejad, S. ,
Mohammadpoor baltork, I. ,
Fallah, H. ,
Dastjerdi, M.J.V. ,
Modayemzadeh, H.R. Materials Research Bulletin (00255408) 46(4)pp. 615-620
In this work, the preparation of In2O3-ZnO thin films by electron beam evaporation technique on glass substrates is reported. Optical and electrical properties of these films were investigated. The effect of dopant amount and annealing temperature on the optical and electrical properties of In2O3-ZnO thin films was also studied. Different amount of ZnO was used as dopant and the films were annealed at different temperature. The results showed that the most crystalline, transparent and uniform films with lowest resistivity were obtained using 25 wt% of ZnO annealed at 500 °C. © 2010 Elsevier Ltd © 2011 Elsevier Ltd. All rights reserved.
Yousefi, M.H. ,
Abdolhosseinzadeh a.a., ,
Fallah, H. ,
Khosravi a.a., Modern Physics Letters B (02179849) 24(25)pp. 2591-2599
A fast-chemically capping method in aqueous solution was developed to synthesize CdS and CdS:Ag luminescent nanoparticles and particles with sizes between 24 nm. The achieving of well-dispersed and narrow-sized particles in colloidal solution and also, high stability of them using mercaptoethanol (ME) as a capping agent was established. Quantum confinement effect was observed in UV-vis absorption as well as in PL spectra. PL spectroscopy also showed green emission and Ag dopants caused a faster energy transfer between CdS inter-bands. XRD patterns exhibited that both cubic and hexagonal phases exist in solutions. Ultimately, TEM images captured from QDs displayed the shapes of nanoclusters which are almost spherical. © 2010 World Scientific Publishing Company.
Optics Express (10944087) 18(12)pp. 12304-12310
Compound eye is a new field of research about miniaturizing imaging systems. We for the first time introduce a dual compound eye that contains three micro lens arrays with aspheric surfaces. The designed dual compound eye in one state is a superposition system in which each channel images all of field of view of the system. With adding a field stop we have decreased the stray light. MTF of ideal superposition compound eye calculated. Also with changing field stop the system is converted to an apposition compound eye in which each channel images only a part of total field of view and so the field of view is larger than that of superposition type. © 2010 Optical Society of America.
Renewable Energy (09601481) 35(7)pp. 1527-1530
In this study, indium tin oxide (ITO) thin films were preparedon glass substrate by electron beam evaporation technique and then were annealed in air atmosphere at 350 °C for 30 min. Increasing substrate temperature (Ts) from 25 to 380°°C reduced sheet resistance of ITO thin films from 150(Ω/□) to 14(Ω/□). The UV-visible-near IR transmittance and reflectance spectra were also confirmed that the substrate temperature has significant effect on the properties of heat reflecting thin films. High transparency (83%) over the visible wavelength region of spectrum and (over 90%) reflectance in near-IR region were obtained at Ts = 300° C. Plasma wavelength, carrier concentrations (ne) and refractive index of the layer were also calculated. The allowed direct band gap at the temperature range 100-300° C was estimated to be in the range 3.71-3.89 eV. Band gap widening due to increase in substrate temperature was observed and is explained on the basis of Burstein-Moss shift. XRD patterns showed that the films were polycrystalline. High quality crystalline thin films with grain size of about 40 nm were obtained. © 2009 Elsevier Ltd. All rights reserved.
Raoufi, D. ,
Fallah, H. ,
Kiasatpour, A. ,
Hasan rozatian, A.S. Applied Surface Science (01694332) 254(7)pp. 2168-2173
In this work, we developed the multifractality and its formalism to investigate the surface topographies of ITO thin films prepared by electron beam deposition method for various annealing temperatures from their atomic force microscopy (AFM) images. Multifractal analysis shows that the spectrum width, Δα (Δα = α max - α min ), of the multifractal spectra, f(α), can be used to characterize the surface roughness of the ITO films quantitatively. Also, it is found that the f(α) shapes of the as-deposited and annealed films remained left hooked (that is Δf = f(α min ) - f(α max ) > 0), and falls within the range 0.149-0.677 depending upon the annealing temperatures. © 2007 Elsevier B.V. All rights reserved.
Journal of Modern Optics (13623044) 54(1)pp. 67-76
The interest in miniaturizing imaging systems has increased recently. This paper discusses aberration calculation and the design of a superposition compound eye, which contains three microlens arrays with aspheric surfaces. The simulation of micro-optical systems, especially those including microlens arrays is still a challenging task. The paper describes simulation and optimization of a superposition compound eye system using geometrical and diffraction-based methods, and some commercial optical design software. Many previously reported superposition compound eyes are in fact apposition compound eyes because each channel images only a part of the field of view (FOV). This paper details the design of a superposition compound eye in which each channel images all the FOV of the system.
Physica E: Low-Dimensional Systems and Nanostructures (13869477) 39(1)pp. 69-74
Indium tin oxide (ITO) thin films with composition of 9.42 wt% SnO2 and 89.75 wt% In2O3, and impurities balanced on glass substrates at room temperature were prepared by electron beam evaporation technique and then were annealed in air atmosphere at different temperatures from 350 to 550 °C for 1 h. XRD pattern showed that increasing annealing temperature increased the crystallinity of thin films and at 550 °C, high-quality crystalline thin films with grain size of about 37 nm were obtained. Increasing annealing temperature also increased conductivity of ITO thin films. Carrier densities (ND) and the flat-band potentials (EFB) were calculated by using electrochemical impedance spectroscopy (EIS). EIS results showed an enhancement in carrier densities and a shift of the flat-band potential to more positive values as the annealing temperature was increased. The UV-visible transmittance spectra were also confirmed that the annealing temperature has significant effect on the transparency of thin films. The highest transparency over the visible wavelength region of spectrum (93%) obtained at 550 °C on annealing temperature. This result was equivalent with those values that have already been reported but with higher level (20 wt%) tin-doped indium oxide thin films and also at 350 °C substrate temperature. The allowed direct band gap at the annealing temperature range 350-550 °C was estimated to be in the range 3.85-3.97 eV. Band gap widening with an increase in annealing temperature was observed and is explained on the basis of Burstein-Moss shift. A comparison between the electron beam evaporation and other deposition techniques showed that the better figure of merit value can be obtained by the former technique. © 2007 Elsevier B.V. All rights reserved.
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.
Raoufi, D. ,
Kiasatpour, A. ,
Fallah, H. ,
Hasan rozatian, A.S. Applied Surface Science (01694332) 253(23)pp. 9085-9090
In this study, the electron beam evaporation method is used to generate an indium tin oxide (ITO) thin film on a glass substrate at room temperature. The surface characteristics of this ITO thin film are then investigated by means of an AFM (atomic force microscopy) method. The influence of postgrowth thermal annealing on the microstructure and surface morphology of ITO thin films are also examined. The results demonstrate that the film annealed at higher annealing temperature (300 °C) has higher surface roughness, which is due to the aggregation of the native grains into larger clusters upon annealing. The fractal analysis reveals that the value of fractal dimension D f falls within the range 2.16-2.20 depending upon the annealing temperatures and is calculated by the height-height correlation function. © 2007 Elsevier B.V. All rights reserved.
Fallah, H. ,
Varnamkhasti, M.G. ,
Hassanzadeh, A. ,
Steki, H. Materials Research Bulletin (00255408) 42(3)pp. 487-496
Tin doped indium oxide (ITO) thin films with composition of 9.42 wt% SnO2 and 89.75 wt% In2O3, and impurities balanced on glass substrates at room temperature have been prepared by electron beam evaporation technique and then were annealed in air at different temperatures from 350 to 550 °C for 1 h. XRD pattern showed that increasing annealing temperature increased the crystallinity of thin films and at 550 °C high quality crystalline thin films with grain size of about 37 nm were obtained. Conductivity of ITO thin films was increased by increasing annealing temperature and conductivity obtained results in 350-550 °C temperature range were also excellently fitted in both Arrhenius-type and Davis-Mott variable-range hopping conductivity models. The UV-vis transmittance spectra were also confirmed that the annealing temperature has significant effect on the transparency of thin films. The highest transparency over the visible wavelength region of spectrum (93%) obtained at 550 °C on annealing temperature. It should be noted that this thin film was deposited on substrate at room temperature. This result obtained is equivalent with those values that have already been reported but with high-level (20 wt%) tin doped indium oxide thin films and also at 350 °C substrate temperature. The allowed direct band gap at the temperature range 350-550 °C was estimated to be in the range 3.85-3.97 eV. Band gap widening with an increase in annealing temperature was observed and is explained on the basis of Burstein-Moss shift. A comparison between the electron beam evaporation and other deposition techniques showed that the better figure of merit value can be obtained by the former technique. At the end we have compared our results with other techniques. © 2006 Elsevier Ltd. All rights reserved.
Optics InfoBase Conference Papers (21622701)
Micro lens lithography does not impose any limit on the mask and on the size of wafer area. The design details of a lens system for micro lens lithography are discussed in this paper. This system contains three micro lens arrays with aspheric surfaces. We simulate and optimize this system and increased resolution with geometrical and diffraction-based methods and using available commercial optical design software. © 2006 Optical Society of America.
Hajiesmaeilbaigi f., ,
Mohammadalipour a., ,
Sabbaghzadeh j., ,
Hosseinkhani, S. ,
Fallah, H. Laser Physics Letters (1612202X) 3(5)pp. 252-256
Silver nanoparticles were produced by irradiating a silver plate with 1064 nm laser beam in pure water. The effect of the laser fluence and ablation time on the ablation efficiency was studied. Fragmentation of the ablated colloid solution by subsequent treatment with 1064 and 532 nm laser pulses yield redistribution of nanoparticles to a smaller mean size. A graph is presented. Absorbance spectrum of silver colloids prepared by different laser fluence. © 2006 by Astro Ltd.
Fallah, H. ,
Varnamkhasti, M.G. ,
Hassanzadeh, A. ,
Steki, H. Physica B: Condensed Matter (09214526) 373(2)pp. 274-279
Tin-doped indium oxide (ITO) thin films with composition of 9.42 wt% SnO2 and 89.75 wt% In2O3, and impurities balanced have been prepared by electron beam evaporation on glass substrates with different deposition rates at fixed low substrate temperature condition. Subsequently, the films were annealed at 400 °C in a thermal furnace for 1 h in air atmosphere. Hereafter, the films were quenched until room temperature and then have been characterized using X-ray diffraction and UV-visible spectroscopy. The lattice constant and the grain size of all thin films were derived to be 10.118 Å and 37 nm in diameter, respectively. A transmittance value of 92% in the visible wavelength region at room substrate temperature was obtained. A similar value was already reported for high-level (20 wt%) tin-doped indium oxide thin films at 350 °C substrate temperature. The resistivity of the films was found to be 7×10-4 Ω cm for the deposition rate of 0.05 nm s-1. Results showed that by decreasing the deposition rate, a lower resistivity and a higher transmittance were obtained at the lower substrate temperature. The obtained values were better than those reported by other authors. Further optical studies showed that in these films allowed indirect transitions can take place. The direct optical energy gap deduced from the optical transmittance data using the Tauc relation was estimated to be 3.80 eV. Resistivity measurements showed that by decreasing the deposition rate, highly conductive transparent films can be obtained. Finally, it has been found that the deposition rate is a very important factor in controlling the electrical and optical properties of ITO films. © 2005 Elsevier B.V. All rights reserved.
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.
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.
Proceedings of SPIE - The International Society for Optical Engineering (1996756X) 5249pp. 740-745
The different methods of optical systems' optimization such as Newton and Least Squares along with their modification are discussed. Monte-Carlo technique as an statistical method which can overcome the shortcoming of those 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 other ones. An numerical example is presented to verify the method.
