H. Abu-Safia

Rugate filter sidelobe suppression using half-apodization

Rugate filters reflectance spectra were calculated for various index profiles with half-Gaussian modulation; graded-index as well as step-index profiles were used. The results show excellent sidelobe suppression around the stopbands, relatively high optical density, and good flatness in the reflectance band.

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 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.

Magneto-dielectric anisotropy in magnetic fluids determined from magneto-optical measurements

Abstract Magneto-optical measurements on magnetic fluids have been utilized to determine the magneto-dielectric anisotropy effect in magnetic fluids. Our results show that the dielectric constant, e| ∗ , seen by light polarized in the direction of the applied magnetic field increases with the field, while e ⊥ ∗ seen by light polarized normal to the field decreases with the field. Moreover, the results also show that e | ∗ exhibits a peak with temperature while e ⊥ ∗ exhibits a minimum. Our calculated results are in good agreement with those obtained using conventional impedance measurement techniques, with the advantage that this method is not affected by the electrode effect, parasitic impedances, skin depth and accuracy-related problems that are typical of conventional impedance measurement techniques.

ac susceptibility of cobalt in mercury magnetic fluids

The temperature dependence of the frequency‐dependent magnetic susceptibility χ’ has been measured for tin‐coated cobalt particles dispersed in mercury, in the temperature range 80–290 K and for a driving frequency of 10 kHz. A rounded maximum in χ’ was observed at certain temperature below the melting point of the mercury Tm. For T≳Tm, a rapid increase of χ’ with temperature is observed. This maximum disappeared for the heat‐treated sample. The results show that χ’(T) follows a Curie–Weiss behavior for TB<T<Tm, with positive ordering temperatures for the three samples. The results were analyzed within the context of Neel theory of superparamagnetism.

The Curie–Weiss behavior of birefringence in ferrofluids

Measurements of birefringence in an Fe3O4 magnetic fluid with isopar‐M as a liquid carrier were undertaken as a function of temperature for 100<T<320 K and in magnetic fields up to 2 kOe. The results show that the birefringence increases with temperature exhibiting a maximum at a certain temperature Tm. The position of Tm decreases with increasing field intensity. For T≳Tm the birefringence follows a Curie–Weiss‐type behavior. The ordering temperature changes not only in magnitude but also in sign with increasing field intensity, being negative for H≳500 Oe.

Does Curie-Weiss behavior exist in the birefringence and dichroism in magnetic fluids?

Abstract The Curie-Weiss behavior of the birefringence, δ, and dichroism, Δ A , in magnetic fluids have been investigated. The analysis of our experimental data on both δ and Δ A in Fe 3 O 4 particle magnetic fluids in the temperature range 100 T T > T m , where T m is the temperature at which the maxima in δ and Δ A take place, and a Vogel-Fulcher type behavior for T T m . This behavior of δ and Δ A with temperature is similar to the behavior of the viscosity of a magnetic fluid with temperature. Therefore, it is suggested that the viscosity of the magnetic fluids plays a major role in the induced optical anisotropy in magnetic fluids.

Calculated and measured reflectivity of some p-type SiC polytypes

In this work, we performed measurements of reflectivity in the energy range 1–6 eV at room temperature for 4H and 6H p-type SiC polytypes. The optical constants of these samples were determined. Experimental results were compared to theoretical calculations based on Kramers–Kronig relations. A good agreement between the experimental and calculated values of reflectivity was obtained.

On the temperature dependence of the ac susceptibility of Fe3O4 magnetic fluids

On the Temperature Dependence of the AC-Susceptibility of an Fe 3 O4 Magnetic Fluids، للحصول على النص الكامل يرجى زيارة مكتبة الحسين بن طلال في جامعة اليرموك او زيارة موقعها الالكتروني