Mark Stevenson

Experimental and theoretical (e, 2e) studies of argon (3p) ionization in asymmetric geometry

Experimental and theoretical triple-differential cross sections (TDCS) are presented for ionization of the outer 3p shell of argon by 200 eV electrons scattered through an angle of 15° and for ejected electron energies of 2, 5, 10 and 20 eV. A distorted-wave Born approximation (DWBA) and a hybrid DWBA-R-matrix (DWBA-RM2) calculation both reproduce the shapes of the TDCS when the slow electron is ejected near the momentum-transfer direction. Near the opposite direction, the DWBA-RM2 model also achieves good agreement with experiment for the higher ejected electron energies, but discrepancies are observed for the lower energies. This three-way joint study emphasizes that it is essential to include a proper treatment of exchange in modelling low-energy ionization.

Excitation?ionization of the calcium atom by electron impact

Double differential cross sections, measured using an electron–photon coincidence method, are reported for the 4p 2P3/2 excited state of Ca+ produced by electron interaction with the 4s2 1S ground state of the calcium atom. The cross section at an incident electron energy of 400 eV is dominated by indirect processes involving 3p excitation to states lying 31.4–31.6 eV above the atomic ground state. These then autoionize to the observed 4p 2P3/2 ion state. Other indirect processes involving states with binding energies in the range 27–41 eV, including triply excited states, are also observed. Preliminary measurements of the linear Stokes parameters at the peak of the main resonance give P1 = −0.09 ± 0.01 and P2 = 0.01 ± 0.01.

Pleiades Experiments on the NIF: Phase II-C

Pleiades was a radiation transport campaign fielded at the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (LLNL) between 2011 and 2014. The primary goals of the campaign were to develop and characterise a reproducible ~350eV x-ray drive and to constrain a number of material data properties required to successfully model the propagation of radiation through two low-density foam materials. A further goal involved the development and qualification of diagnostics for future radiation transport experiments at NIF. Pleiades was a collaborative campaign involving teams from both AWE and the Los Alamos National Laboratory (LANL).

Quantum Dots in Planar Cavities — Single and Entangled Photon Sources

We show that single InAs quantum dots embedded in a planar cavity, formed by mismatched sets of GaAs/AlAs distributed Bragg reflectors, can be a useful source of triggered single photons as well as polarisation-entangled photon pairs. The former is demonstrated with a second order correlation function under 0.1 and the latter with a fidelity exceeding 70 %. Such quantum dot devices may be useful in quantum communications and quantum information processing.

Spin‐Resolved Collisions of Electrons with Rubidium Atoms: A Search for Relativistic Effects

The search for relativistic effects in electron‐alkali scattering is currently a topic of considerable interest. The A2 spin asymmetry parameter is a direct measure of relativistic effects in the electron‐atom collision process, as it is entirely dependent on the spin‐orbit effect. We present measurements of the A2 spin asymmetry for the 5S → 5P transition in rubidium at incident energies of 15, 20, 30 and 50 eV and for elastic scattering at 15, 20, 30, 50 and 80eV. Our results indicate that under these collision conditions, relativistic effects are measurable, in qualitative agreement with the available theory.

Spin Asymmetries in Elastic and Inelastic Scattering from Rubidium

Experimental and theoretical results are presented for the A2 spin asymmetry for elastic and inelastic scattering of spin-polarized electrons from rubidium, at incident electron energies of 15, 20, 30, 50 and 80 eV. Theoretical calculations are performed within a semi-relativistic Breit–Pauli R-matrix (close-coupling) model. The experimental data reveal significant asymmetries at all energies. The experimental results are reasonably well described by the present theoretical calculations and by other calculations using a relativistic distorted-wave approach, and provide a clear relativistic signature.

Semiconductor Light Sources for Applications in Quantum Optics

Applications in optical quantum information technology require the development of a new type of light source for which exactly one photon is emitted periodically. We review here recent progress in using semiconductor quantum dots as the active medium for generating single photons. Anti-bunching and single photon emission is observed both for optical and electrical injection of the recombining electrons and holes into the dots.