JOURNAL OF THEORETICAL AND APPLIED PHYSICS (IRANIAN PHYSICAL JOURNAL)
Year:2014 | Volume:8 | Issue:3|Papers Count:8

The intensity distributions near the focal point for tight focusing of azimuthally polarized Laguerre–Gaussian beam including higher order modes are calculated based on vector diffraction theory. For higher order as well as the fundamental lower order mode A-TEM01*, a small focal hole at the centre is obtained for the focusing under high NA lens. In a limit of NA=0.95, the higher order A-TEMp1* mode beams of p=1, 2, 3, 4, 5 and 6 are established numerically in detail. It is observed that one of the higher order mode A-TEM51* generates some interesting results. And it is also observed that the intensity distribution of the different mode has little variation among the degree of truncation (b) of the input beam beside the pupil. This work is important for optical manipulation, optical data storage, micro-machines and optical trapping applications for low refractive index particles.

Field theory is applied to analyze the behavior of the electromagnetic wave in the presence of a solid electron beam and magnetized plasma-loaded tape helix traveling-wave tube. The obtained dispersion relation implicitly includes azimuthal variations and all spatial harmonics of the tape helix. Results indicate that the frequency and the phase velocity of (Xbp − Xp) and (Obp − Xp ) modes increase with cyclotron frequency and for (Obp − Op) and (X bp − Op ) modes decrease. In the strong magnetic field limit, the maximum growth rate and frequency of all modes are constant at different values of cyclotron frequency and beam energy. If the plasma density increases, the frequency and phase velocity of four modes will increase. The maximum growth rates of the four modes in the lower plasma density are equal and for higher values of plasma density the (Obp − Xp) mode has greatest value. The phase velocity and the frequency of (Xbp − Xp) with (Xbp − Op) modes and (Obp − Op) with (Obp− Xp) modes are coinciding with each other and for first case increase with beam density, but for latter decrease. The maximum growth rate of (Obp − Op) mode and the maximum frequency of (Xbp − Xp) mode have highest values as a function of the electron beam density.

Theoretical calculations are carried out for studying soliton’s reflection and transmission in an inhomogeneous plasma comprising ions, two temperature electrons and negatively charged dust grains. Using reductive perturbation technique, relevant modified KdV equations are derived for the incident, reflected and transmitted solitons. Then a coupled equation is obtained based on these mKdV equations, which is solved for the reflected soliton under the use of solutions of mKdV equations corresponding to the incident and transmitted solitons.Based on the ratio of amplitudes of reflected and incident solitons, reflection coefficient is examined under the effect of dust grain density; the same is done for the transmission coefficient which is the ratio of amplitudes of transmitted and incident solitons. The transmission of the solitons becomes weaker under the effect of stronger magnetic field and higher dust density. However, this leads to the stronger reflection of the soliton.

In this work, the copper films were deposited on quartz substrates by DC magnetron sputtering method and then, the prepared films were annealed in air atmosphere at different annealing temperatures. Before annealing, some of the copper films, treated by oxygen plasma, for comparison of the results. The structural and morphological properties of the films have been investigated using X-ray diffraction (XRD), atomic force microscopy, and four point probe techniques.XRD results exhibited that the cuprous oxide phase changes to cupric oxide by enhancing of annealing temperatures. Also, oxygen plasma treatment can cause the better crystallinity for the prepared copper oxide films. The results confirm that oxygen plasma treatment, affected the crystal size, grain size, average roughness, sheet resistivity and strain of the films. The optical characteristics of the oxygen plasma treated films, such as refractive index, extinction coefficient and absorption coefficient were calculated by straight forward method proposed by Swanepoel using transmittance measurements.Moreover it was found that annealing temperature augmentation lead to decrease the optical band gap energy calculated using Tauc’s relation from 2.45 to 1.80 eV.

To obtain a suitable ohmic contact with the lowest resistivity, chromium (Cr) thin films were deposited on transparent conductive oxide indium tin oxide (ITO) by RF sputtering method in argon atmosphere and its electrical properties were optimized. The deposition of Cr thin film has been performed for the layers with thickness of 150, 300 and 600 nm in constant Ar gas flow of 30 SCCM.Results show that the lowest contact resistivity belongs to the layer with 600 nm thickness. Furthermore, Cr/ITO has been studied for five different RF powers of 100, 150, 200, 250 and 300 W. Experimental results show that specific contact resistance of Cr/ITO contact decreases in condition of depositing chromium thin films on ITO at higher RF powers. Analysis of SEM has been performed on the samples. The SEM micrographs show Cr thin films have smaller grains at RF power of 150 W, in comparison with other RF powers. The lowest specific contact resistivity for Cr/ITO has been obtained 4.79 10-2 X cm2 at RF power of 150 W with 600 nm thickness of chromium thin films.

The canonical function method (CFM) is a powerful accurate and fast method that solves the Schrodinger equation for the eigenvalues directly without evaluating the eigenfunctions. In this work, it is applied to the solution 1D Schrodinger equation specializing to the linear potential that is perturbed by electric field. The linear and square Stark effects are perturbation terms. Finally, the CFM results will be compared with the exact results. The CFM method is superior to many standard techniques that have been used to solve the Schrodinger equation such as Numervo.

The propagation of spherical (or cylindrical) shock wave in an ideal gas with or without gravitational effects in the presence of a constant azimuthal magnetic field is investigated. Non-similarity solutions are obtained for isothermal flow between the shock and the piston. The numerical solutions are obtained using the Runge–Kutta method of the fourth order. The density of the gas is assumed to be varying and obeying an exponential law.The shock wave moves with variable velocity, and the total energy of the wave is non-constant and varies with time.The effects of variation of the Alfven-Mach number, gravitational parameter and time are obtained. It is investigated that the presence of gravitational field reduces the effect of the magnetic field. Also, the presence of gravitational field increases the compressibility of the medium, due to which it is compressed and, therefore, the distance between the inner contact surface and the shock surface is reduced. The shock waves in conducting perfect gas can be important for description of shocks in supernova explosions, in the study of central part of star burst galaxies, nuclear explosion, rupture of a pressurized vessel and explosion in the ionosphere. Other potential applications of this study include analysis of data from exploding wire experiments and cylindrically symmetric hypersonic flow problems associated with meteors or re-entry vehicles etc.A comparison is made between the solutions in the cases of the gravitating and the non-gravitating medium with or without magnetic field. The obtained solutions are applicable for arbitrary values of time.

In this article, we investigate and apply Hamiltonian approach method as one of the analytical approximate techniques, for studying the strongly nonlinear dynamical systems such as the motion of a rigid rod rocking back on the circular surface without slipping and the free vibrations of an autonomous conservative oscillator with inertia and static-type fifth-order nonlinearities. To illustrate the applicability and accuracy of the method, the approximate solution results are compared with exact and numerical solutions.