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Islamabad, Pakistan

Ashraf M.,Optics Laboratories | Akhtar S.M.J.,Optics Laboratories | Khan A.F.,Pakistan Institute of Engineering and Applied Sciences | Ali Z.,Optics Laboratories | Qayyum A.,Pakistan Institute of Nuclear Science and Technology
Journal of Alloys and Compounds | Year: 2011

Thin films of ZnSe were deposited on soda lime glass substrates by thermal evaporation and annealed in vacuum at various temperatures in the range of 100-300 °C. Structural and optoelectronic properties of these films were investigated and compared with the available data. XRD studies revealed that as-deposited films were polycrystalline in nature with cubic structure. It was further observed that the grain size and crystallinity increased, whereas dislocations and strains decreased with the increase of annealing temperature. The optical energy band gap estimated from the transmittance data was in the range of 2.60-2.67 eV. The observed increase in band gap energy with annealing temperature may be due to the quantum confinement effects. Similarly, refractive index of the films was found to increase with the annealing temperature. The AFM images revealed that films were uniform and pinhole free. The RMS roughness of the films increased from 1.5 nm to 2.5 nm with the increase of annealing temperature. Resistivity of the films decreased linearly with the increase of temperature. © 2010 Elsevier B.V. All rights reserved.

Ilyas B.,Pakistan Institute of Engineering and Applied Sciences | Dogar A.H.,Pakistan Institute of Nuclear Science and Technology | Ullah S.,Pakistan Institute of Nuclear Science and Technology | Mahmood N.,Optics Laboratories | And 2 more authors.
Laser and Particle Beams | Year: 2012

Plasma was generated by focusing 10 ns Nd:YAG (λ = 1064 nm) laser pulse on the thick tungsten target. The laser fluence at the target was varied in the range of 3.57-10.97 J/cm2. The ion emission from the expanding tungsten plasma was analyzed with the help of an ion collector and time-of-flight electrostatic ion energy analyzer. About 44 times rise in the ion charge per laser shot was observed in the investigated laser fluence range. The measured threshold fluence for onset of the tungsten plasma was 3.27 J/cm 2. The estimated plume expansion coefficient Z inf/X inf = 2.5 ± 0.2 was in agreement with the previous experimental studies and the predictions of self-similar plume expansion model. The electrostatic ion energy analyzer study showed that charge state of the W ions increases with the laser fluence and maximum ion charge state was 5+. It was observed that threshold fluence for appearance of a specific charge state can be measured. A clear correlation between the relative abundances of W(n-1)+, W n+, and W(n+1)+ indicates that higher order charge states are most probably produced by stepwise ionization process. Copyright © 2012 Cambridge University Press.

Aqili A.K.S.,Hashemite University | Ali Z.,Optics Laboratories
Journal of Crystal Growth | Year: 2011

ZnTe thin films were deposited by the two-source evaporation technique on amorphous glass substrate. The deposited films were annealed under nitrogen ambient pressure. The resistivity of the film annealed under nitrogen pressure of 100 mbar was found to be less than that of as-deposited film by more than four orders of magnitude. The films structures were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The films′ thickness and the optical properties such as refractive index, absorption coefficient and optical band gap of the films were determined from transmittance spectra in the wavelength range of 4002000 nm. The dark electrical conductivity of the films was studied as a function of temperature to determine the DC conductivity activation energy of the films. © 2011 Elsevier B.V. All rights reserved.

Shah A.,Pakistan Institute of Nuclear Science and Technology | Saeed R.,Pakistan Institute of Nuclear Science and Technology | Noaman-Ul-Haq M.,Optics Laboratories
Physics of Plasmas | Year: 2010

The cylindrical and spherical Korteweg-de Vries-Burger equations have been derived to study the ion acoustic converging and diverging shock waves. The considered plasma is comprised of inertialess electrons, positrons, and inertial thermal ions. It is noticed that the ion temperature, positron concentration, and kinematic viscosity have significant influence on the shock structure and propagation in nonplanar geometries. The strength of shock in spherical geometry is found to dominate over shock strength in cylindrical geometry. The shock wave strength and steepness escalate with time as it moves towards the center and shock enervates as it recedes away from center. The graphical view of the numerical results is presented for illustration. The results may have relevance in the inertial confinement fusion plasmas. © 2010 American Institute of Physics.

Ali I.,University of Lyon | Ali I.,Optics Laboratories | Mille J.,University of Lyon | Mille J.,University Claude Bernard Lyon 1 | Tougne L.,University of Lyon
Pattern Recognition Letters | Year: 2012

Background models are used for object detection in many computer vision algorithms. In this article, we propose a novel background modeling method based on frequency for spatially varying and time repetitive textured background. The local Fourier transform is applied to construct a pixel-wise representation of local frequency components. We apply our method for object detection in moving background conditions. Experimental results of our frequency-based background model are evaluated both qualitatively and quantitatively. © 2012 Elsevier B.V. All rights reserved.

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