Saleh T. Mahmoud

Beat-wave excitation of electron plasma wave by cross-focusing of two intense laser beams

This paper presents the cross-focusing of two intense laser beams in a collisionless plasma, taking into account the relativistic non-linearity. The non-linearity is not bound to large irradiances and this non-linearity is only a perturbation. It should be noted here that while considering the self-focusing due to relativistic electron mass variation, the electron ponderomotive density depression in the channel may also be important. Therefore, these two non-linearities may simultaneously affect the self-focusing process. In the present paper we have considered the situation when only relativistic non-linearity is important. The non-linearity due to relativistic mass variation depends not only on the intensity of one laser but also on the second laser. Therefore, one laser beam affects the dynamics of the second beam and hence a cross-focusing process takes place. The electric field amplitude of the excited electron plasma wave (EPW) has been calculated and its effect on the cross-focusing process has also been discussed. It is observed that the inclusion of a resonantly excited EPW on cross-focusing is significant and the accelerating electric field of the generated EPW becomes affected. A comparison of the theory with the recent experimental observations has also been presented.

Electrical properties of Se2Sb2Te6 thin films

The electrical properties of Se2Sb2Te6 thin films are investigated using dc resistance, impedance spectroscopy and capacitance–voltage (C–V) measurements. The amorphous–crystalline transition temperature, Tc, is estimated to be 60 °C using dc resistance measurements. The impedance spectroscopy measurements are performed at different temperatures ranging from 25 to 95 °C. The impedance spectroscopy data give an estimation of the activation energy, Ev = 0.5 eV. The amorphous–crystalline interface is electrically characterized by measuring the capacitance of the film as a function of bias voltage at different temperatures ranging from 25 to 85 °C. The C–V measurements show temperature dependence and nonlinear behaviour of the capacitance with the applied bias voltages that could be attributed to the crystallization growth as the temperature gets close to Tc.

Generation of Plasma Wave at Pump-Wave Frequency and Second Harmonic Generation at Ultrarelativistic Laser Power

In this paper, the influence of ponderomotive and relativistic nonlinearities on the filamentation of an ultraintense laser pulse is investigated in three dimensions within the paraxial ray approximations. Generation of electron plasma wave (EPW) structure at pump-wave frequency and the second harmonic generation in these filamentary structures are reported. The generation of the plasma wave is due to intensity gradient (in the transverse direction of the laser beam in filamentary structure) and density gradient (due to ponderomotive-force effect). For typical laser-plasma parameters: The laser intensity = 2.5 times1020 W/cm2; the particles density = 1.9 times 1019 cm-3; and it is found that the maximum intensity of EPW is in the range of 2.0 times 1013 W/cm2. Interaction of the plasma wave with the incident laser beam leads to second harmonic generation, and the yield comes out to be ap 2.1 times 10-7.

Use of Light Traps and Differing Light Color to Investigate Seasonal Abundance of the Date Palm Pest, Oryctes agamemnon arabicus (Coleoptera: Scarabaeidae)

ABSTRACT Oryctes agamemnon arabicus (Fairmaire) (Coleoptera: Scarabaeidae) is a date palm insect pest that causes damage to trunk and roots and can damage grass lawns in the United Arab Emirates (UAE) and other countries such as Oman, Saudi Arabia, and Tunisia. The goal of this study was to monitor population dynamics and to evaluate six light colors (white, green, red, yellow, blue, and infrared) and two lamp types (mercury and energy-saving) in light traps. Experiments were performed on a date palm farm during a 2 yr period (2010 and 2011). It was found that this insect is a univoltine pest with a single population peak. Adults appeared in the field around middle of April and early May and the population continued to build until maximum numbers were reached in mid June. No adults were found after the end of September. Photoperiod showed a significant correlation with the changes in adult population size. White light emitted from mercury lamps attracted significantly more O. agamemnon arabicus adults compared with the other tested light colors. Increasing the wattage of mercury lamps from 160 to 250 watt did not significantly increase the number of collected insects. The results demonstrated that light traps equipped with 160-watt mercury lamps emitting white light collected significantly the highest number of this insect among the other tested lamps.

Electrical and optical properties of indium-modified Se 2 Sb 2 Te 6 films

The electrical and optical characteristics of indium-doped Se2Sb2Te6 phase-change alloy are studied in this paper. It is found that adding indium to Se2Sb2Te6 alloy increases its amorphous‐crystalline transition temperature, TC, and reduces the electrical conduction activation energy. The capacitance‐temperature measurements showed a drastic change in the capacitance of the modified film as the temperature approaches TC and eventually the capacitance becomes negative and nonlinear. The negativity and nonlinearity in the capacitance‐voltage dependence can be attributed to the growth of conductive crystalline islands with increasing temperature.

Production and Growth Mechanisms of Pd Nanoclusters

Size-selected palladium nanoclusters have been produced by dc sputtering and inert gas condensation technique using mixtures of argon and helium gases. By controlling the source parameters, it was possible to produce Pd nanoclusters with size in the range of 2-10 nm. Transmission electron microscopy (TEM) images were used to confirm the produced sizes of nanocluster. It was found that increas- ing the percentage of helium to argon have two main effects: i) decreases the nanocluster size as a result of the high drift velocity of he- lium, and ii) decreases the number of measured nanoclusters due to the low sputtering yield of helium. Since He gas is primarily respon- sible for the cluster-condensation process, its partial pressure can be used to control the nanoclusters growth. The source parameters and their effects on the size and number of nanoclusters are of great importance in understanding the Pd nanoclusters growth mechanism.

Production of Size-Selected CuXSn1-X Nanoclusters

Composites of copper–tin (CuxSn1-x) nanoclusters were synthesized using the magnetron dc sputtering gas–condensation technique. Targets with controlled ratios of Sn to Cu were used to produce CuxSn1-x with different compositions. The effects on the nanocluster size and yield of the sputtering discharge power, inert gas flow rate, and aggregation length were investigated using a quadrupole mass filter. The sputtering discharge power was optimized to maximize the nanocluster yield. The results show that as the inert gas flow rate increases the nanocluster size increases and then decreases. These dependences could be understood in terms of the dominant nanocluster production mechanisms. This work demonstrates the ability of controlling the CuxSn1-x nanoclusters’ size and composition by optimizing the source operation conditions.

Stimulated Brillouin back-scattering at relativistic laser power

The effect of ultra intense laser beam filaments on stimulated Brillouin scattering (SBS) has been investigated in collisionless and unmagnetized plasma when relativistic and ponderomotive nonlinearities are operative. The pump depletion and self-focusing effects of the pump and backscattered laser beams are taken into account in three dimensions within the paraxial ray approximations. It is found that Brillouin back-reflectivity decreases when ponderomotive and relativistic nonlinearities are operative. Integrated reflectivity is found to exhibit a maximum value at optimum SBS gain when the self-focusing effect is taken into account. The SBS back-reflectivity continuously increases with GSBS when the self-focusing effect is excluded. The reflectivity with pump depletion is less than without pump depletion.

Higher-order paraxial theory of the propagation of ring rippled laser beam in plasma: Relativistic ponderomotive regime

This article presents higher-order paraxial theory (non-paraxial theory) for the ring ripple formation on an intense Gaussian laser beam and its propagation in plasma, taking into account the relativistic-ponderomotive nonlinearity. The intensity dependent dielectric constant of the plasma has been determined for the main laser beam and ring ripple superimposed on the main laser beam. The dielectric constant of the plasma is modified due to the contribution of the electric field vector of ring ripple. Nonlinear differential equations have been formulated to examine the growth of ring ripple in plasma, self focusing of main laser beam, and ring rippled laser beam in plasma using higher-order paraxial theory. These equations have been solved numerically for different laser intensities and plasma frequencies. The well established experimental laser and plasma parameters are used in numerical calculation. It is observed that the focusing of the laser beams (main and ring rippled) becomes fast in the nonparaxi...

Electrical and Optical Properties of Indium-Modified SeSbTe Thin Films for Low Power Memory Devices

The electrical and optical characteristics of indium doped Se2Sb2Te6 phase-change alloy are studied. It is found that adding indium to Se2Sb2Te6 alloy (In0.3Se2Sb2Te6) increased the crystallization temperature and reduced the electrical conduction activation energy. The capacitance-temperature measurements showed a drastic change in the capacitance of the modified film when the temperature approaches the crystallization temperature, and eventually the capacitance becomes negative and nonlinear. The negativity and nonlinearity in the capacitancevoltage dependence can be attributed to the growth of conductive crystalline islands by increasing the temperature.