Showing papers in "Indian Journal of Pure & Applied Physics in 1998"

Electronic Structure of Disordered Alloys

Abstract: The last decade has seen a rapid progress in understanding the electronic structure of disordered alloys and in this article I shall review the progress made by using the Kohn-Korringa-Rostoker (KKR) based approaches. The KKR approach in conjuction with the coherent-potential approximation (CPA) has emerged as a powerful tool to study the electronic structure of disordered alloys. This method called, KKR- CPA, combined with the local density approximation (LDA) provides a first-principles, parameter-free mean-field theory for treating electronic structure of a disordered alloy. Insofar as the average properties are concerned, the KKR-CPA replaces the disordered system by a suitably chosen translationally invariant effective medium, which is determined self-consistently. To illustrate some of its applications I shall present some recent results for Li-Mg and Nb-Mo alloys. Also our recent attempts to go beyond the KKR-CPA and to include short-range order will be briefly discussed.

Laser gain studies of rhodamine 6g dye doped polymer laser

Abstract: Solid state dye doped polymer is an attractive alternative to the conventional liquid dye solution. In this paper, the laser characteristics of Rhodamine 6G (Rh6G) doped polymethyl methacrylate (PMMA) rods, modified with ethyl alcohol (EtOH), are examined by nitrogen laser, and second harmonic Nd : YAG laser excitations in a transverse pumping configuration and the variation of small signal gain of the dye in solid medium for different pump powers are studied. The photobleaching of dye doped polymer rod is also studied.

Application of spatial-coherence spectroscopy for determining the angular diameters of stars: feasibility experiment

Abstract: An experiment is performed in which a new method is used to determine the coherence properties of the wave fields, produced by a broadband source, from the spectral changes produced on interference in the Young's double slit experiment. The knowledge of spectral degree of coherence obtained experimentally combined with the space-frequency equivalence theorem is used to determine the angular diameter of the star which is the source of the field. This is the first experiment showing the application of spatial-coherence spectroscopy in astronomy.