JOURNAL OF SCIENCES (ISLAMIC AZAD UNIVERSITY)
Year:2006 | Volume:16 | Issue:59 (PHYSICS ISSUE)|Papers Count:9

In this present paper we report a mathematical analysis of absorptive bistability either in combination with self-fousing or in the absence of it in bulk ZnSe at room temperature, at 80-300 miliwatt power levels, for the 476-nm visible wavelength. This method is based on the nonlinear variations of temperature-dependent absorption coefficient near the band edge. It has been also obtained some theoretical input-output curves, showing hysteresis loop, that clearly reproduce the main qualitative features of the experiments with generally good quantitative agreement. In addition, changes in the hysteresis loops have been considered when the two parameters of thickness of the sample and size of the input beam have been changed.

Wakefield generation by femtosecond laser pulse in its interaction with ionized gas is described. The amplitude of the wakefield Ap is studied as a function of laser pulse and background gas parameters and is compared with results of preliminary ionized plasma Api. It is found that ionization process can increase Ap compared to Api. The effect of polarization of laser beam on the wakefield amplitude is studied and linear and circular polarizations are compared. Differences between the effects of square and Gaussian beam shapes in the intensity of Ap are investigated. The strongest enhancement Ap in comparison with Api takes place for longer laser pulse with a duration in excess of plasma wave period when the resonant conditions of pondermotive excitation of the wakefield are not matched.

The subject of radiation damage in silicon by plasma and electron beam technique has been investigated for many years. Modification for having particular surface topography is also sometimes desired specially in those experiments that ion interaction with surface is very sensitive to the surface topography. In our previous work in order to study the electron bombardment effect on silicon, we used our new design electron source. In this paper, silicon samples were bombarded by 30 keV argon ions on normal to the surface with doses in the 1×1016-2×1017 Ar+/cm2 range. Topographical changes induced on silicon surface, generation of blisters and evolution of them at different doses observed by atomic force microscopy. Measurement of mean surface height show that for doses greater than 1×1017 Ar+/cm2 the height decreases because of sputtering. The optical properties of samples after Ar+ irradiation measured by a UV-Vis-NIR spectrophotometer.

As the volume ignition of deuterium-tritium (D-T), deuterium-helium-3 (D-3He) and deuterium-deuterium (D-D) fuels have been numerically modeled, hydrogen-boron (H-11B) fuels are no investigated, and its energy efficiency and ignition conditions are examined. It is shown that, the predicted compression the H-11B laser fusion requires 100 times the maximum estimate for compression of D-T. Thus, although the ultimate goal would be to progress toward H-11B fuel, the results suggest that inertial confinement fusion (ICF) operation with H-11B is impossible in the near future.

The motion of relativistic test electron in a free electron laser can be altered significantly by an ideal coaxial wiggler field and uniform axial guide field. We have investigated group I, II and III orbits and finally have found that electron motion become chaotic at sufficiently high beam density and at sufficiently high amplitude of wiggler field. The threshold value of the wiggler amplitude for the onset of chaos is estimated analytically and confirmed by computer simulation. It is shown that the electron dynamic is nonintegrable. There is evidence for chaos from numerical calculation of Poincare maps and nonzero Lyapunov exponent using different approaches of Benettin's method which are described and compared. Moreover, it is shown that the particle motion become chaotic on a time scale comparable with the beam transit time through a few wiggler periods.

We report on the fabrication of Ti2AlN in this article. Thin films of the Mn+1AXn phase ( M: early transition metal; A: A-group element; X: C and/ or N; n=1-3) Ti2AlN were grown on Ti, Si and glass substrate from a Ti and Al compound target with an Ar/N2 gas mixture using DC magnetron sputtering system. X-ray diffraction and atomic force microscopy (AFM) were used to characterize the Ti2AlN (004) structure and morphology of the samples.

In this paper, an analytical and experimental model will be presented, to study the effect of waves and currents interaction phenomena. In this experiments we will consider the viscosity effect and sea bed roughness .This model has been drived by using the general form of the so called (N-S) Equations of motions, and shear stress calculations which are a Combinations of theory and experiments in this field .Our major concern will be to define and express the governning dimensionless parameters in a such complicated phenomena. The results of experiments data will be good compared by Brevik of Ass1 (1980), van rijn3 (1993) and Jonsson5 (1976).Finally the experimental analysis shows that, the dimensionless parameter developed in present study , have essentially reasonable agreement with the theory.

This work presents the results of a low energy nitrogen ion implantation of AISI 304 type stainless steel (SS) at moderate temperatures of about 500oC. The nitrogen ions are extracted from a Kauffman type ion source at a Energy of 30 keV, and ion current density of 100 mA cm-2. In our study the nitrogen dose of 6×1017, 8×1017 and 1018 ions cm-2, were selected. The X-ray diffraction results show the formation of CrN polycrystalline phase after nitrogen bombardment and a change of crystallinity degree due to the dose effect the image analysis of implanted samples clearly shows significant changes in surface. Corrosion test has shown that corrosion resistance is enhanced by increasing dose.

The massive, negatively charged dust grains are considered as discrete particles, while the electrons and ions assume to be distributed by Boltzmannean with the same temperatures. Assuming the grains to be conductors and charge of grain depend on the surface potential of the grain. The Poisson equation for small potentials takes then the form of the Helmholtz equation. The spatial distribution of the potential in the lattice includes the effect of whole system of dust particles. Such a self consistent description gives the dispersion relation for the dust lattice waves. It is shown that for the existence of ideal lattice the dusty plasma parameters must satisfy the definite relation. The calculations are carried out for two dimensional hexagonal lattice putting the cyclic boundary condition on dust grains. New relation for potential is found and there is a comparison with Yukawa system.