Sharif Digital Repository

We propose a new system which can generate digital holograms using natural color information. The proposed system can generate about 10 digital holographic video frames per a second using about 6K light sources  

The behavior of an electrified liquid jet breakup and modes of disintegration were investigated at different flow rates and voltages. The current phenomenology belongs to a new injector introduced recently by Morad et al. (2016). This injector has proven to highly extend the stability and flow rate of electrospray particularly in the Taylor cone-jet mode. The experimental investigation was performed using a high-power light-emitting diode (LED) illumination as the light source. The light source was developed to operate in the pulsing condition when synchronized with a digital camera and was particularly designed to function properly in the presence of high electromagnetic interference (EMI).... 

In this study the output beam profiles of the single mode and multimode optical fibers are investigated by the cross sectional imaging technique. Different experiments are performed for the single mode and multimode fibers and the captured images are compared. The relative near field intensity distribution and their relative changes with respect to the distance is examined and some fiber parameters are obtained. A similar pattern in the real-time image is observed for the two type fibers and major differences are discussed. Using this method it is possible to determine the numerical aperture of the illuminated fiber, which is about 0.22 for the tested fiber. The effect of coherency of the... 

Design and operation of an opto-mechanical system for spectral analysis using a double fiber design for light delivery are reported in this study. A simple mechanical drive system is used, which is able to perform a fine course of angular motion for the scanning of the dispersive optical element. The presented system consists of a mechanical drive system, a dispersive element, a double fiber assembly and a photodetector. A source light, a digital multimeter and a PC are used to test the presented design. The first-order diffraction of the white light source is obtained by using a reflection diffraction grating in Littrow arrangement. By comparing the output reflection signals of the plane... 

This research presents an application of transparent lanthanum-modified lead zirconate titanate (PLZT) materials in micro light source tracking device, which is designed to function as a result of irradiation, having neither lead wires nor electric circuits. The focus of the paper is on the analytical and finite element investigation into ultraviolet photo-induced multi-physics responses of PLZT photocantilever and a comparison of the measured bending displacement to check the feasibility of these materials in design of micro light source tracking device. The finite element formulation of the transverse deflection for multi-physics analysis of PLZT ceramics by including the photovoltaic and... 

Quantum yield relations were extended by adding effective conditional parameters in photodegradation of organic pollutants such as intensity of light, wavelength of light, average distance from light source, concentrations of dye/pollutant and photocatalyst, and volume of reactor. The geometry of light source and thin film and particulate photocatalytic systems were considered in analysis. Extended quantum yield that is a dimensionless factor is applicable in various types of dye and photocatalyst. This extended quantum yield allowed us to classify photodegradation as reported by scientific groups, performed in various operational conditions in order to identify the degree of similarity... 

X-ray Powder Diffraction beamline is one of the first priorities of Iranian Light Source Facility day-onebeamlines. This beamline will cover the research requirements of scientific community in the fields of physics, material science, chemistry, etc and also have benefits for industries. This paper shortly reports the ray tracing calculations for the optical design of this beamline. The results show that bending magnet source would satisfy the nowadays users requirements, although insertion device should also be considered for covering the requirements of the future users. In this paper the effects of the optical elements on the users' requirements have been discussed to obtain the... 

A new dimensionless parameter, Sh-factor, is introduced by using dimensional analysis and extending the quantum yield definition to show power-law relations among light intensity, light wavelength, distance from light source, concentrations of dye/pollutant and photocatalyst, time, and degradation percent. The Sh-factor has the same equation form for photoactivated remediation systems with particulate and thin-film photocatalysts, and it provides mathematical tools to predict degradation performance of a photocatalytic system. These power-law equations separate simply the operational parameters related to the lamp from semiconductor photocatalyst characteristics. The light scattering and... 

A structure is suggested for spasing. The presented surface plasmon amplification by stimulated emission of Radiation (SPASER) is made up of a graphene nanosphere, which supports localized surface plasmon modes, and a quantum dot array, acting as a gain medium. The gain medium is pumped by an external light source. Since all the plasmons are carried on a graphene platform, the structure features coherent surface plasmons with high confinement and large life time. All the structures are analyzed theoretically using full quantum mechanical description. The main advantage of the proposed SPASER is its simple tuning capability of changing graphene's Fermi level, which is performed by either... 

Brain Computer Interface provides a new communication channel for people who have severe brain injuries. Among different types of BCIs, SSVEP-based one has been focused in recent years. In this type of BCI, selection of twinkling frequency of external visual stimulant and the distance between stimulants (in case of more than one stimulant) is so important. In this work, a SSVEP-based BCI with two external stimulants was designed. In order to determine the best twinkling frequency of stimulants and the best distance between them, the classification accuracy for seven different twinkling frequency pairs and five different stimulants distances was calculated. Two methods for feature extraction... 

This paper proposes an enhanced illumination compensation algorithm, which can compensate for the uneven illuminations on human faces and reconstruct face images in normal lighting conditions. To detect the illumination category, based on 65 categories in YaleB database, the images processed using Block-based Histogram Equalization (BHE) is compared with the original face image processed using histogram equalization (HE). Based on the identified illumination category, a quadratic model is used to reconstruct an image that will visually be under normal illumination. In order to avoid the effect of light source intensity on face images, we used HE method. Experimental results show that, by... 

Steady-State Visual Evoked Potentials (SSVEPs) are one of the most important EEG signals used in Human Computer Interface (HCI) systems. These signals are generated by Looking at flickering external light sources stimulating the central part of the retina. By increasing the number of external light sources, detection of the corresponding SSVEPs from the recorded EEG signal becomes more complicated. On the other hand, the ratio of the sensitivity to specificity in high-speed classifiers becomes more significant. This study presents the effect of the twinkling frequencies and the inter-sources distance of two Light Emitting Diodes (LEDs) on the ratio of the sensitivity to specificity of the... 

The photocatalytic decolorization of aqueous solutions of Direct Red 27 in the presence of various amounts of semiconductor powder suspensions has been investigated in a batch reactor with the use of artificial light sources. ZnO and TiO2 have been found the most active photocatalysts; the effect of catalyst loading and type on the reaction rate was optimized for maximum degradation. The results imply that 1:1 ratio is proper for the photocatalytic removal of Direct Red 27. In addition, the effects of particle size and surface area were examined in this photocatalytic process. The results showed that the decolorization efficiency increases with increase in surface area, and decrease in... 

The comprehensive optical-electrical-gain-thermal self-consistent model of the 1.55 μm AlGaInAs Photonic Crystal vertical cavity surface emitting diode lasers (PhC VCSELs) with buried tunnel junction (BTJ) has been applied to optimize its threshold characteristics. It shows that, for 5 μm devices, the room temperature (RT) threshold current equal to only 0.59 mA and maximum operating temperature equal to as much as 380 K. Results suggest that, the 5 μm AlGaInAs PhC VCSELs seem to be the most optimal ones for light sources in high performance optical communication systems  

Line nanopatterns are produced on the positive photoresist by scanning near-field optical microscope (SNOM). A laser diode with a wavelength of 450 nm and a power of 250 mW as the light source and an aluminum coated nanoprobe with a 70 nm aperture at the tip apex have been employed. A neutral density filter has been used to control the exposure power of the photoresist. It is found that the changes induced by light in the photoresist can be detected by in situ shear force microscopy (ShFM), before the development of the photoresist. Scanning electron microscope (SEM) images of the developed photoresist have been used to optimize the scanning speed and the power required for exposure, in... 

Organic-inorganic halide perovskites (OIHPs) have emerged as a promising semiconductor for the fabrication of efficient optoelectronic devices such as photodetectors (PDs). Among all the perovskite compositions, the mixed-halide MAPb(BrxI1-x)3 formulations have gained more attention for photodetection application thanks to their tunable optoelectronic properties and great stability. However, there is still a lack of sufficient understanding of the effect of Br doping on the stability and physical properties of MAPb(BrxI1-x)3 based PDs. In this work, we prepare a series of MAPb(BrxI1-x)3 (x = 0, 0.04, 0.08, 0.12, and 0.16) single crystals (SCs) and investigate the influence of the Br content... 

A new photocatalyst (Ag-S/PEG/TiO2) was synthesized by adding polyethylene glycol (PEG) to an efficient Ag-S/TiO2 photocatalyst, to obtain a photocatalyst that is highly active under visible light. In addition to Ag-S/PEG/TiO2, Ag-S/TiO2 and pure TiO2 were prepared to compare their properties and activities. Specifically, the morphologies and microstructures of the nanophotocatalysts were characterized by means of powder X-ray diffraction (XRD), N2 adsorption-desorption measurements, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) microanalysis, transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy,... 

In this study power transmission modulation for different fibers in a fiber-to-fiber design using two different light sources is reported. A fiber-to-fiber arrangement is used in which the source light is directly coupled to the first fiber and the second fiber delivers the light to a power meter. Arrangements with three sets of different type fibers are tested in this study and output powers are monitored with the white lamp or red LED as illumination light sources. Using this arrangement the variations of the power as a result of axial (Z-direction) and lateral (X- and Y-direction) displacements of the second fiber are monitored. Theoretical models are also used to evaluate the power... 

In this paper, we propose what we believe is a novel sensitive micro-optoelectromechanical systems (MOEMS) accelerometer based on intensity modulation by using a one-dimensional photonic crystal. The optical sensing system of the proposed structure includes an air-dielectric multilayer photonic bandgap material, a laser diode (LD) light source, a typical photodiode (1550 nm) and a set of integrated optical waveguides. The proposed sensor provides several advantages, such as a relatively wide measurement range, good linearity in the whole measurement range, integration capability, negligible cross-axis sensitivity, high reliability, and low air-damping coefficient, which results in a wider...