N.A. Yusuf

Velocity measurements of sputtered atoms in excited states

Abstract The decay of intensity as a function of the distance from the target surface has been measured for a number of transitions from excited states in several species of sputtered atoms. The experimental data are fitted to two different models from which the velocity component normal to the target surface and the threshold kinetic energy for the excited atoms can be derived. The implications of the results to the excitation process in sputtering are discussed.

Field and concentration dependence of chain formation in magnetic fluids

The field and concentration dependence of chain formation in magnetic fluids is investigated. The results show that the chain length increases rapidly with the field and then continues to increase gradually at higher fields approaching saturation. Moreover, the results show that the chain length at a given field is linear with the concentration of the fluid. The correlation between chain formation and some magneto-optic effects is discussed.

Determination of Faraday rotation in a ferrofluid

Abstract Transmission of plane polarised light through ferrofluids in the presence of a magnetic field parallel to the direction of propagation depends on both chain formation and Faraday rotation. A procedure is proposed to separate between both factors. Faraday rotation in a dilute Fe 3 O 4 ferrofluid measured by this procedure does not show saturation in fields up to 4000 G.

Transmission of a Gaussian beam through a Fabry–Perot interferometer

The transmission of a Gaussian beam through a Fabry-Perot interferometer (FPI) has been investigated. The equation for the electric field of the transmitted beam was derived and then the transmitted irradiance I(t) was numerically calculated for different selected parameters of both the FPI and the beam. The results show that the energy profile of the transmitted beam has been distorted to different degrees depending on the various parameters of the Gaussian beam and the FPI. Moreover the results show that the positions of the peaks of the transmitted beam are shifted, especially for intermediate waists for which the arctan term is nonlinear. The results also show that for nonnormal incidence successive transmitted beams are spatially separated and are not interfering appreciably with each other.

The temperature dependence of the optical anisotropy in magnetic fluids: birefringence and dichroism

Abstract The temperature dependence of birefringence, δ, and dichroism, Δ A , in Fe 3 O 4 Isopar-M based magnetic fluids have been investigated in the temperature range 100 T T s , and then both increase with temperature until they reach a maximum at a temperature T m , and then decrease with temperature for T > T m . The values of T m and T s are found to vary with concentration and the applied field. The results also show that δ- H 2 and Δ A-H 2 curves deviate from linearity. This deviation is attributed to interparticle interactions, the orientation of pre-existing clusters, and the field-induced chain formation.

The wavelength dependence of Faraday rotation in magnetic fluids

Measurements of Faraday rotation over the wavelength range 450–633 nm in a dilute Fe3O4 particle magnetic fluid are reported. The results, in agreement with the theory, show an enhancement of Faraday rotation near the wavelength λ≊500 nm.

On the concentration dependence of Faraday rotation in magnetic fluids

Faraday rotation and magnetization measurements at room temperature were undertaken on Fe/sub 3/O/sub 4/ particle magnetic fluids with different concentrations. The results show that Faraday rotation follows a Langevin-type behavior with the applied magnetic field. The results also show that Faraday rotation increases with the concentration of the sample and tends to saturate at higher fields for higher concentration. By comparing the optical and magnetic data the role of chain formation in Faraday rotation is discussed. From these measurements, the chain length at given field is found to be linear with the concentration of the sample, a result that is in agreement with recent studies on the concentration dependence of chain formation. >

Faraday rotation and chain formation in magnetic fluids

The Faraday rotation in Fe/sub 3/O/sub 4/ particle magnetic fluids with different concentrations has been measured. The results show that Faraday rotation increases with concentration and tends to saturate at higher fields for higher concentrations. The role of chain formation in Faraday rotation has been investigated by studying samples with the same concentration but with different surfactant contents and by studying the effect of the sample thickness. The results suggest that chain formation has an important role. >

Does local thermodynamic equilibrium exist in the excitation process of sputtered atoms

Abstract The optical line intensities from a series of ion-bombarded oxide glasses are fitted to two different equations relating the intensity and the energy of the upper level. The plots suggest that the existence of local thermodynamic equilibrium in the excitation process during sputtering is unlikely.

The wavelength and concentration dependence of the magneto-dielectric anisotropy effect in magnetic fluids determined from magneto-optical measurements

The concentration and wavelength dependence of the magneto-dielectric anisotropy effect in magnetic fluids has been investigated. Our results show that the field-induced change in the dielectric constants for light polarized in the field direction increases with the applied field while that for light polarized perpendicular to the field decreases with the field. Furthermore, our results show that this field-induced change is linear with concentration. The results also show that the field-induced change, for light polarized in the field direction, increases with frequency till it reaches a peak at a given frequency and then decreases with further increase in frequency; while for light polarized perpendicular to the field, it decreases with frequency till it reaches a minimum at a given frequency and then increases with further increase in frequency. Moreover, our results yield a value of two for the magneto-dielectric anisotropy factor.