Islamabad, Pakistan
Islamabad, Pakistan

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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.


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.


Werbowy S.,University of Gdansk | Kwela J.,University of Gdansk | Anjum N.,Optics Laboratories | Huhnermann H.,University of Marburg | Windholz L.,University of Graz
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

Using the high-resolution spectroscopic method of collinear laser-ion-beam spectroscopy (CLIBS), the Zeeman effect of singly ionized praseodymium spectral lines has been studied at relatively small magnetic fields up to 330 G. With this unusual method for studying the Zeeman effect of ionic lines we recorded Zeeman-hyperfine structure patterns with clearly resolved components with linewidths as low as 60 MHz, which is only sometimes the natural linewidth. From the Zeeman patterns of 30 lines, improved Landé gJ factors were determined for 39 Pr ii levels of the 4f35d, 4f25d2, and 4f36p configurations. © 2014 American Physical Society.


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.


Skrobol C.,Max Planck Institute of Quantum Optics | Skrobol C.,Ludwig Maximilians University of Munich | Ahmad I.,Max Planck Institute of Quantum Optics | Ahmad I.,Optics Laboratories | And 9 more authors.
Optics Express | Year: 2012

On the quest towards reaching petawatt-scale peak power light pulses with few-cycle duration, optical parametric chirped pulse amplification (OPCPA) pumped on a time scale of a few picoseconds represents a very promising route. Here we present an experimental demonstration of few-ps OPCPA in DKDP, in order to experimentally verify the feasibility of the scheme. Broadband amplification was observed in the wavelength range of 830-1310 nm. The amplified spectrum supports two optical cycle pulses, at a central wavelength of ∼920 nm, with a pulse duration of 6.1 fs (FWHM). The comparison of the experimental results with our numerical calculations of the OPCPA process showed good agreement. These findings confirm the reliability of our theoretical modelling, in particular with respect to the design for further amplification stages, scaling the output peak powers to the petawatt scale. © 2012 Optical Society of America.


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.


Ul Haq M.N.,Optics Laboratories | Saeed R.,Pakistan Institute of Nuclear Science and Technology | Shah A.,Pakistan Institute of Nuclear Science and Technology
Journal of Applied Physics | Year: 2010

The propagation of ion acoustic shock waves in cylindrical and spherical geometries has been investigated. The plasma system consists of cold ions, Boltzmannian electrons and positrons. Spherical, cylindrical Korteweg-de Vries-Burger equations have been derived by reductive perturbation technique and their shock behavior is studied by employing finite difference method. Our main emphasis is on the behavior of shock as it moves toward and away from center of spherical and cylindrical geometries. It is noticed, that the shock wave strength and steepness accrues with time as it moves toward the center and shock enervates as it moves away from center. The strength of shock in spherical geometry is found to dominate over shock strength in cylindrical geometry. Positron concentration, kinematic viscosity are also found to have significant effect on the shock structure and propagation. The results may have relevance in the inertial confinement fusion plasmas. © 2010 American Institute of Physics.


Butt S.,Institute of Space Technology | Butt S.,National University of Sciences and Technology | Shah N.A.,COMSATS Institute of Information Technology | Nazir A.,Italian Institute of Technology | And 2 more authors.
Journal of Alloys and Compounds | Year: 2014

Polycrystalline CdS thin films were deposited on glass substrates by close spaced sublimation technique. Samples of various thicknesses, ranging from 250 to 940 nm were obtained. The optical and electrical properties of pure CdS thin films were studied as a function of film thickness. The resistivity of as-deposited CdS films was in the order of 106-108 Ω cm, depending upon the film thickness. In the high temperature region, carriers are transported over the grain boundaries by thermionic emission. Resistivity was reduced to the order of 10-2-101 Ω cm by the thermally diffusion of indium into CdS films, without changing the type of carriers. The annealing temperature dependence of structural, optical and electrical properties of In-doped CdS films showed that the samples annealed at 350 °C and 400°C exhibited better results. © 2013 Elsevier B.V. All rights reserved.


Rauf A.,Pakistan Institute of Engineering and Applied Sciences | Mehmood M.,Pakistan Institute of Engineering and Applied Sciences | Ahmed M.,Optics Laboratories | ul Hasan M.,Pakistan Institute of Engineering and Applied Sciences | Aslam M.,Pakistan Institute of Engineering and Applied Sciences
Journal of Luminescence | Year: 2010

Photoluminescence (PL) of the anodic alumina has been studied and related with quality of hexagonal ordering of the pores. The photoluminescence excitation (PLE) spectra have been successfully de-convoluted into primarily two sub-bands with peak positions at about 355 and 395 nm and maximum emission at about 450 and 500 nm, respectively; the former being assigned to F+ centers and the latter to the F-centers. A red shift in the PLE takes place, at a given anodizing voltage, when the quality of the hexagonal pore ordering deteriorates with an increase in number density of defects, i.e., pentagons and hexagons with missing pores. The metallic hills at these defects change the curvatures of the metal-oxide and the oxide-electrolyte interfaces that could affect the field distribution and hence the stress-state and other characteristics of the oxide at the defects. This allows a comparatively larger concentration of F centers (395 nm band), causing a red shift in the PLE with increase in defect density. © 2009 Elsevier B.V. All rights reserved.


Aqili A.K.S.,Hashemite University | Saleh A.J.,Hashemite University | Ali Z.,Optics Laboratories | Al-Omari S.,Hashemite University
Journal of Alloys and Compounds | Year: 2012

ZnTe thin films were deposited by closed space sublimation (CSS) technique on amorphous glass substrate. The deposited films were immersed in AgNO 3 solution for different time periods, then heated in vacuum. The resistivity of the film, immersed for 30 min, was reduced by less than six orders of magnitudes. The films structures were characterized by X-ray diffraction (XRD). Atomic force microscope (AFM) was used to detect the surface morphology of the films. The films thickness, the optical properties, such as refractive index, absorption coefficient and the optical band gap were determined from transmittance spectra in the wavelength range of 400-2500 nm. The dark electrical conductivities of the films were studied as function of temperature to determine the conductivity activation energy. © 2011 Elsevier B.V. All rights reserved.

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