Electronic structure of Ni-Cu alloys studied by spectroscopic ellipsometry

Ellipsometric measurements of the complex dielectric functions of Ni and Ni1−cCuc alloys (c=0.1,0.3,0.4) have been carried out in the (1.2–5.5)-eV region. Two structures in the σ1 spectrum of pure Ni at about 1.5 and 4.7 eV are attributable to direct interband transitions in the band structure of ferromagnetic Ni. As the Cu concentration increases, the 4.7-eV edge (from transitions between the s-d–hybridized bands well below EF and the s-p-like bands above EF, e.g., X1→X’4) shifts to higher energies, while the 1.5-eV edge (from transitions between a p-like band below EF and a dband above EF along the L–W direction, e.g., L’2→L3) remains at the same energy. A structure grows in the (2–3)-eV region as Cu is added, and it is interpreted to be due to the transitions between the localized Cu subbands. All these observations are in accord with the calculated (coherent-potential-approximation) electronic structure of Ni-Cu alloys.This article is from Physical Review B 39 (1989): 9882, doi:10.1103/PhysRevB.39.9882. Posted with permission</p

The phenomenon of nonlinear optical birefringence in uniaxial crystals

Birefringence is a phenomenon that produces double - value nature of refractive indices in uniaxial crystals. This phenomenon gives rise to effects such as ordinary (o) and extraordinary waves (e) and Kerr effect which produces nonlinear coefficients called Kerr constants. In this work, twelve uniaxial crystals are considered. The minimum electric field intensity that is required to produce nonlinear birefringence is determined. The magnitudes of the nonvanishing dielectric tensor components and their corresponding critical angles have been evaluated for the twelve uniaxial crystals. The result shows that in negative uniaxial crystals, electromagnetic waves travel faster in the extraordinary axis than in the ordinary axes. The reverse is however obtained in positive uniaxial axis. The work has also provided the series to be employed when determining the Kerr constants for even order nonlinear coefficients. A motivation for this work is an attempt to make nonlinear optical phenomena accessible to physics undergraduate.Birrefringencia es un fenómeno que produce el doble - valor natural de los índices de refracción en cristales uniaxiales. Este fenómeno da lugar a efectos como el ordinario (o) y las olas extraordinarias (e) y el efecto Kerr, que produce coeficientes lineales constantes llamados Kerr. En este trabajo, doce cristales uniaxiales son considerados. El mínimo de intensidad de campo eléctrico que se requiere para producir la birrefringencia lineal se determina. Las magnitudes de las componentes del tensor dieléctrico no nula y sus ángulos correspondientes críticos han sido evaluados para doce crsitales uniaxiales. El resultado muestra que en cristales uniaxiales negativos, las ondas electromagnéticas viajan más rápido en el eje extraordinario que en los ejes comunes. Sin embargo, es lo contrario obtenidos en un eje uniaxial positivo. El trabajo también ha proporcionado la serie que se emplea para determinar las constantes de los coeficientes de Kerr, incluso para no lineal. Una motivación para este trabajo es un intento de hacer los fenómenos ópticos no lineales de acceso a la licenciatura de Física