Photodetachment of negative hydrogen ion in circularly polarized monochromatic and bichromatic laser fields

We theoretically have investigated the detachment of negative hydrogen ion in circularly polarized monochromatic and bichromatic laser fields by calculating the photoelectron momentum distributions (PMDs). We find that the PMDs are controlled by the electric field of laser pulse. For circularly polarized monochromatic laser fields, the PMDs are perfect and isotropic rings, and the photodetachment rates in random direction are same. For this case, the photoelectron momentum spectra directly reflect the electronic distributions of negative hydrogen ion. For circularly polarized bichromatic laser field, the PMDs are inversion asymmetric, but symmetric about a certain axis. The emission directions of the photoelectrons vary with the electric field shape, that is to say that the emission directions of the photoelectrons vary with the carrier-envelope (CE) phases, which decide the electric field of laser pulse. The maximal photodetachment rates and the spectra shape, however, are same for the different CE phases.     

Commutation Rules and Eigenvalues of Spin and Orbital Angular Momentum of Radiation Fields

Abstract

We investigate the separation of the total angular momentum J of the electromagnetic field into a ‘spin’ part S and an ‘orbital’ part L. We show that both ‘spin’ and ‘orbital’ angular momentum are observables. However, the transversality of the radiation field affects the commutation relations for the associated quantum operators. This implies that neither S nor L are angular momentum operators. Moreover their eigenvalues are not discrete. We construct field modes such that each mode excitation (photon) is in a simultaneous eigenstate of S _z and L _z. We consider the interaction of such a photon with an atom and the resulting effect on the internal and external part of the atomic angular momentum.     

Stagnant vortex flow

With the aid of the vorticity transport equation it is shown that in inviscid, incompressible, axially symmetric vortex flow the axial vorticity component near the axis of the vortex approaches zero if the axial velocity component approaches a stagnation point, and vice versa, the axial vorticity component is increased, if the axial flow is accelerated. This result, obtained in earlier investigations by simplifying the momentum equations for the neighborhood of the axis of the vortex, is already contained in the vorticity transport equation as formulated by von Helmholtz in 1858. In laminar flow, with viscous forces acting near the stagnation point, the angular velocity does not necessarily vanish with the axial velocity component. These questions are discussed in the following.     

An analysis of the angular momentum of a light field in terms of angular harmonics

Abstract

This paper proposes an optical interpretation for the Lie algebra's symmetry operators of the paraxial wave equation. In particular, the angular momentum operator is used to derive a relation for the expression of the angular momentum of an arbitrary light field in terms of angular harmonics. Furthermore, experimental results are presented demonstrating a filter that extracts angular harmonics from different Gauss-Laguerre modes.     

Radar and scattering parameters through falling hydrometeors with axisymmetric shapes

Falling raindrops and other hydrometeors have, in general, nonspherical shapes and mean canting angles that are due to aerodynamic and gravitational forces. We use the T matrix and the quantum theory of angular momentum to compute extinction matrices, scattering and absorption cross sections, backscattering matrices, and, from these quantities, radar parameters. A monodisperse population of rain with axially symmetric distribution over orientations where the axis of symmetry is the local direction of air flow about the raindrops is considered. Oblate spheroids with axial ratios that depend on size and appropriate series of Chebyshev polynomials were assumed for definition of the shapes of raindrops. Computations were performed at common microwave frequencies for several temperatures, incidence angles, and degrees of particle wobble about a preferred orientation. Results reveal the importance of the role of orientation distribution and particle size and the shape of radar parameters in these computations for a region of moderate-sized raindrops.     

Quantum Dynamics of a Nonlinear Birefringent Model with Anticorrelated Field States

Abstract

In this paper, anticorrelated field states with a binomial distribution over orthogonal polarizations, interacting with a nonlinear birefringent medium, are discussed. The field states are the SU(2) coherent states, where the angular momentum operators are realized as bilinear products of the boson operators associated with the two polarizations. The system discussed here provides an optical realization of a nonlinear rotator. We study the quantum dynamics of the statistical properties of the field and the evolution of the degree of polarization.     

Focusing of axially symmetric flattened Gaussian beams

Abstract

We study the three-dimensional field distribution of a focused axially symmetric flattened Gaussian beam. In particular, exact closed-form expressions for the intensity along the optical axis and at the focal plane are provided, together with a comparison between our results and those pertinent to the case of a converging spherical wave diffracted by a hard-edge circular aperture. Some hints for future investigations are also given.     

Multiphoton One-step Ionization of Helium at 1064 nm

Abstract

The multiphoton ionization of helium by a strong radiation field having a wavelength of 1064 nm and a field intensity up to 5 × 10¹⁴ W cm ^?2 is considered within a non-perturbative treatment partially accounting for the electron-electron correlations in the initial bound state and approximately for the Coulomb interaction between the residual ion and the ejected electron in the final state. Only single-electron transitions are considered, the main emphasis being on the field polarization effects. The obtained results are compared with the few results available in the literature in the same regime as well as with very recent experimental findings. In particular, the calculated photoelectron energy spectra, angular distributions and ionization rates are found to reproduce satisfactorily all the main features observed in the experiments. The proposed formalism appears to be a particularly flexible method for studying field polarization effects; for the channel-by-channel analysis in the case of strong fields; and for multiphoton processes of very large order. Potential development and improvement of the technique is discussed.     

Angular Momentum Balance on Light Reflection

Abstract

It was pointed out by Holbourn in 1936 that there is an apparent breakdown of angular momentum conservation on reflection of circularly polarized light at the plane interface between two lossless dielectrics. The analysis presented in this paper shows that this discrepancy does not arise provided that: (a) the intensities of the incident, reflected, and transmitted beams vanish at large distances from their axes, and (b) the angular momentum of each beam is calculated from first principles.     

Estimation of oxidation states of AlOx barriers in a tunneling junction by inelastic electron tunneling spectroscopy

Co/AlO_x/Co with AlO_x barriers of various oxidation states were fabricated and investigated using inelastic electron tunneling (IET) spectroscopy and X-ray photoelectron spectroscopy (XPS). XPS revealed that AlO_x oxidized for 8 h contained an inhomogeneous distribution of metallic Al, whereas AlO_x oxidized for 24 h contained a homogeneous distribution. The inhomogeneous and homogeneous distributions of metallic Al corresponded to asymmetric and symmetric IET spectra, respectively. These junctions showed peaks at ± 0.03 V. AlO_x oxidized for 168 h contained no metallic Al, and this junction had no peaks, suggesting that peaks at ± 0.03 V originate from metallic Al.     

Geometric phase in optics and angular momentum of light

Abstract

The Physical mechanism of the geometric phase in terms of angular momentum exchange is elucidated. It is argued that the geometric phase arising out of the cyclic changes in the transverse mode space of Gaussian light beams is a manifestation of the cycles in the momentum space of the light. The apparent non-conservation of orbital angular momentum in the spontaneous parametric down conversion for the classical light beams is proposed to be related to the geometric phase.     

Characterization of oxidized gallium droplets on silicon surface: An ellipsoidal droplet shape model for angle resolved X-ray photoelectron spectroscopy analysis

Deposition and oxidation of metallic gallium droplets on Si(111) were studied by angle resolved X-ray photoelectron spectroscopy. Two gallium peaks - Ga 3d and Ga 2p - were simultaneously measured in order to get an advantage of different inelastic mean free paths of photoelectrons from these two energy levels differing in binding energy by 1100 eV. Together with the angular dependent data it enhances the precision of the size characterization of Ga droplets and oxide thickness determination. A model for the calculation of theoretical intensities based on an ellipsoidal shape of droplets is presented and a simple procedure for estimation of droplet height and actual surface coverage based on measurement on a single emission angle is suggested.     

Cavity field tomography via atomic beam deflection

Abstract

We propose a set-up where a classical field interacts via a two-level atom with a quantized field in a resonator. Due to entanglement we can reconstruct all available information about the field by measuring the momentum distribution of the atom.     

Preparation of macroscopically distinguishable superpositions of circular or linear oscillatory states of a bidimensionally trapped ion

Abstract

A simple scheme for the generation of two different classes of bidimensional vibrational Schrödinger cat-like states of an isotropically trapped ion is presented. We show that by appropriately adjusting an easily controllable parameter having a clear physical meaning, the states prepared by our procedure are quantum superpositions of either vibrational axial angular momentum eigenstates or Fock states along two orthogonal directions.     

Macroscopic jumps of the axial angular momentum variance of a bidimensionally trapped ion

Abstract

The time evolution of the axial angular momentum [Lcirc] _z of an ion confined in a bidimensional trap is investigated. We find that, under suitable initial conditions, the interaction of the ion with two properly configured classical laser beams induces a peculiar dynamical behaviour of the axial angular momentum fluctuations. We show, in fact, that there exists an instant of time at which the variance of [Lcirc] _z undergoes variations proportional to N ² further to a change of one quantum only in the initial total number N ? 1 of vibrational quanta. The non-classical origin of these macroscopic jumps is brought to the light and carefully discussed.     

Optical tweezers and optical spanners with Laguerre–Gaussian modes

Abstract

We numerically model the axial trapping forces within optical tweezers arising from Laguerre–Gaussian laser modes. For an 8 μm diameter sphere suspended in water, the higher-order modes produce an axial trapping force several times larger than that of the fundamental. Partial absorption results in a transfer of the orbital angular momentum from the Laguerre–Gaussian mode to the trapped particle. This results in the rotation of the particle by what may be called an optical spanner (wrench). For an absorption coefficient of α = 5700 m^?1 and a laser power of 10 mW, we find that an 8 μm diameter sphere would acquire an angular acceleration of 10 × 10⁴ rad s^?2 and a limiting angular velocity of 0.2 rad s^?1.     

Quantum-optical Phase and Canonical Conjugation

Abstract

We use a new limiting procedure, developed to study quantum-optical phase, to examine canonically conjugate operators in general. We find that Dirac's assumption that photon number and phase should be canonically conjugate variables, similar to momentum and position, is essentially correct. The difficulties with Dirac's approach are shown to arise through use of a form of the canonical commutator which, although the only possible form in the usual infinite Hilbert space approach, is not sufficiently general to be used as a model for a number-phase commutator. The approach in this paper unifies the theory of conjugate operators, which include photon number and phase, angular momentum and angle, and momentum and position as particular cases. The usual position-momentum commutator is regained from a more generally applicable expression by means of a domain restriction which cannot be used for the phase-number commutator.     

Interaction of CO,NO, and H<Subscript>2</Subscript> molecules on the surface of a Ni/MgO(111) metal oxide system

The adsorption and interaction of carbon monoxide (CO), nitrogen oxide (NO), and hydrogen (H₂) molecules on the surface of a system produced when nanosize nickel clusters are formed on the surface of a magnesium oxide film [MgO (111)] has been studied in an ultrahigh vacuum by IR, thermal desorption, and photoelectron spectroscopy. It is shown that, at a substrate temperature of 85 K, CO and NO molecules at low surface concentrations, are mostly adsorbed on the surface of Ni particles, whereas at higher surface coverage CO molecules are forced to the Ni/MgO(111) interface. The adsorption of hydrogen results in NO molecules also being displaced to the interface. The particular state of the molecules at the interface between the metal and the polar surface of the oxide is responsible for the observed processes in which CO is converted to CO₂ due to the reduction of NO to N₂.