Phase conjugation in magnetized semiconductors by stimulated Brillouin scattering Sen, Pranay K; Sen, Pratima; Vivek, Sarika
doi: 10.1088/0022-3727/29/1/001pmid: N/A
Based upon the density matrix formulations of nonlinear optical susceptibility, optical phase conjugation via stimulated Brillouin scattering (OPC-SPS) in the presence of a moderately high magnetostatic field is studied in centrosymmetric semiconducting crystals under a parabolic approximation. The magnetostatic field B has a twofold contribution to the coherent radiation - semiconductor interaction through the formation of discrete Landau levels and the sharpening of the density-of-states. Numerical estimations made for an InSb sample at low temperature irradiated by a 5.5 to 6.0 m CO laser reveal enhancement in the value of Brillouin susceptibility in the presence of the magnetostatic field B. This in turn lowers the threshold intensity required for the onset of OPC-SBS. A considerably high reflectivity is obtained when B is increased from 1 to 4.02 T. For experimental observation of OPC-SBS as described in the paper, it may be stressed that the polarization of the laser should be properly determined so that the crystal is effectively centrosymmetric.
Reduction of haematite to magnetite induced by hydrogen ion implantation Watanabe, Yoshimi; Takemura, Shinya; Kashiwaya, Yoshiaki; Ishii, Kuniyoshi
doi: 10.1088/0022-3727/29/1/002pmid: N/A
Microstructural changes induced by hydrogen ion implantation in haematite () have been investigated by transmission electron microscopy. It has been found that the hydrogen ion implantation causes the haematite magnetite () reduction at room temperature. From electron diffraction patterns after the hydrogen implantation, the following orientation relationship was found to exist between haematite and magnetite: . Since these results agree with those in previous studies, microstructural changes during the reduction were obtained by using the implantation technique. The reduction mechanism of magnetite from haematite is discussed in terms of the experimental results on crystallographic relationships.
Scaling structure of magnetization anomalies in high-temperature superconductors Khalil, Ali E
doi: 10.1088/0022-3727/29/1/004pmid: N/A
An explanation for the magnetization anomalies recently measured in Y - B - Cu - O and single crystals is provided. This explanation considers the impact of the disordered state and percolation effects in these materials. The scaling behaviour of the low-field minimum in the magnatization curves () as a function of the oxygen deficiency parameter () is deduced. In addition, the temperature-dependence of the secondary peak observed in magnetization curves of single crystals was found to be consistent with the experimental measurements. The model takes into account the random nature of the defect distribution in the two-dimensional planes and the percolation effects due to grain size distributions.
Low-energy ion-beam-assisted deposition and GMR of granular magnetic alloys Guilfoyle, S J; Pollard, R J; Grundy, P J
doi: 10.1088/0022-3727/29/1/006pmid: N/A
Granular Co - Ag and NiFe - Ag thin films were prepared by magnetron sputtering with low-energy (0 - 500 eV) ion radiation assisted deposition. For sputter-only films the giant magnetoresistance (GMR) ratio varied with composition, with a peak occurring at about 35 at.% magnetic component. The ion beam was found to increase the GMR slightly with increasing energy and then progressively decrease it. There was an accompanying decrease in film thickness and Ag concentration as the ion beam preferentially sputtered the Ag. TEM has revealed sputtered films to contain ordered 10 - 20 nm spherical particles whilst the ion-beam-assisted films were made up of a network of particles clustered into channels.
Optical media and target characterization by Mueller matrix decomposition Roy-Bréhonnet, F Le; Jeune, B Le; Eliès, P; Cariou, J; Lotrian, J
doi: 10.1088/0022-3727/29/1/007pmid: N/A
Laser imaging set-ups permit characterization of the vectorial nature of the optical wave which is transmitted by a medium or reflected by a target, from polarimetric formalisms such as Jones or Stokes - Mueller calculi. When the Mueller matrix of targets (or media) is experimentally determined, information about the polarizing and depolarizing properties can be obtained from a Mueller - Jones matrix, which operation requires knowledge of the experimental uncertainties in the elements of . We will discuss the possibility of a polar decomposition of the extracted Mueller - Jones matrix. We then obtain the product of a Hermitian matrix and a unitary matrix, which can be associated with it, for a polarization transformer, with an elliptical partial polarizer and a pure elliptical retarder respectively. Classification of a target is deduced from its polarimetric characteristics (depolarization, polarizing and retardation properties). Experimental Mueller matrices of polarization transformers (media or targets) are provided and analysed by this method in order to characterize the physical behaviour of these optical systems with respect to polarization phenomena.
Error contour charts for the two-wave WKB approximation Jones, A R; Koh, J; Nasaruddin, A
doi: 10.1088/0022-3727/29/1/008pmid: N/A
Error contour charts have been generated comparing scattered intensities calculated using the RGD and the single-wave and two-wave WKB approximations against Mie theory in the range of real refractive index from 1 to 1.5 and of size parameter from 0 to 20. It is demonstrated that the two-wave WKB method is superior to the others. Nonetheless its range of applicability is very limited, especially at scattering angles larger than .}
Gain measurements at 543 nm in helium neon laser discharges Gray, B S; Latimer, I D; Spoor, S P
doi: 10.1088/0022-3727/29/1/010pmid: N/A
A single-mode frequency stable helium neon laser operating on the 543 nm neon transition was used to probe an electrical discharge in helium neon mixtures. Values for the optical gain at this wavelength were obtained. A comparison with the widely documented behaviour of the 633 nm transition, which shares the same upper state as the 543 nm transition, shows a marked difference in the variation of the optical gain with discharge pressure. This is shown to occur due to the differing behaviour of the lower laser state population densities with pressure. It is proposed that this could be due to the resonance peak in the electron excitation cross section from the ground state to the 2 level. Variation of gain with discharge current is also presented.