A. Afaq

The investigation of spherical effects on the photodetached electron spectra

A theoretical imaging method is used to study the induced effects of a spherical surface on the photodetached electron spectra of a mono-atomic negative ion (H−). Analytical formulas are derived for the detached electron flux and the total photodetachment cross section. The radius of the spherical surface strongly affects the spectra of the flux as well as the cross section. The analysis of the spectra reveals that the curvature of the surface controls the oscillations in the spectra, and the plane wall case reported in Afaq and Du (2007 J. Phys. B: At. Mol. Opt. Phys. 40 1309) is a special case of the spherical surface.

Photodetachment of H? near a Hard Spherical Surface

The photodetachment of a hydrogen negative ion (H?) near a hard spherical surface is investigated by using the theoretical imaging method. The surface is oriented in such a fashion that the laser polarization direction is perpendicular to the principal axis of the spherical surface. Analytical expressions are derived for the detached-electron flux and photodetachment cross section. Strong interference patterns are observed in the detached-electron flux, while no visible oscillations are found in the photodetachment cross section.

Linear and nonlinear optical response of MgxZn1−xO: A density functional study

Abstract Total and partial density of states, frequency dependent complex refractive index including extinction coefficient, optical conductivity and transmission of MgxZn1−xO (0≤x≤1) in rocksalt and wurtzite phases are calculated using full potential linearized augmented plane wave (FP-LAPW) method. The real part of refractive index decreases while the extinction coefficient, optical conductivity and transmission for rocksalt phase increases with the increase in Mg concentration. In wurtzite phase, ordinary and extraordinary indices decrease while extinction coefficient, optical conductivity and transmission increase in parallel as well as perpendicular to c-axis with the increase in the Mg concentration.

Investigation of Linear Tetra-Atomic Negative Ion by Photodetached-Electron Spectra

Photodetachment spectra from a linear tetra-atomic negative ion is investigated by treating the detached-electron wave function quantum mechanically. A plane polarized laser light, perpendicular to the axis of the ion, is used to detach the electron from the ion. Analytical expressions for the electron flux and total photodetachment cross section are derived. The electron flux on screen shows strong-energy-dependent oscillations with different frequencies. The total cross section of the tetra-atomic negative ion reduces the cross section of mono-atomic, diatomic and triatomic negative ions for high energy photons, while for low energy photons it becomes four times the cross section of mono-atomic negative ions.

Interferences in Photodetached Electron Spectra from a Linear Tetra-Atomic Negative Ion

Photo-detached electron spectra from a hypothetical linear tetra-atomic negative ion is obtained. A plane polarized laser parallel to the axis of the molecular ion is used to knock off the loosely bound electron. The spectrum of the detached-electron flux shows strong interference peaks, while the number of peaks increases with the increase in the photon energy. Strong oscillations are also observed in the total photodetachment cross section spectrum. The frequency of the oscillations increases with the increase in the distance between the successive atoms d in the linear chain. These quantum interference effects vanish for very large d or very high photon energy.

Oscillations in the photodetachment cross section of a two-centre model

We study analytically the photodetachment cross sections of a two-centre negative ion system based on an extension of the photodetachment model of H−. The photodetachment cross section formulae are derived and found to be strongly oscillatory. We study in detail the dependence of the cross section on the distance between the two centres, photon energy and the laser polarization direction. Closed-orbit theory is extended and used to study the origin for the oscillations in the cross sections. We also derive the oscillatory photodetachment cross section averaged over the orientations of the two-centre system. This study reveals the connection between the oscillations in the cross section and a detached-electron orbit.

Photodetachment of a Homo-Nuclear Linear Tetra-Atomic Negative Molecular Ion

The photodetachment of a homo-nuclear linear tetra-atomic negative molecular ion is studied theoretically for an arbitrary laser polarization. An expression for the total cross section is obtained by using an extended version of the two center model, where each center acts as a source of coherent photodetached-electron waves. Strong oscillations on observation plane, placed at a large distance from the ion, are observed. The amplitude of these oscillations is maximum when the laser polarization is parallel to the molecular axis. Furthermore, the amplitude decreases as the angle between the laser polarization and molecular axis increases and consequently vanishes when they are perpendicular to each other. It is also found that if the distance between the adjacent centers is very small or very large, then the amplitude of oscillations is negligibly small.