227 research outputs found

    Focusing a deterministic single-ion beam

    Full text link
    We focus down an ion beam consisting of single 40Ca+ ions to a spot size of a few mum using an einzel-lens. Starting from a segmented linear Paul trap, we have implemented a procedure which allows us to deterministically load a predetermined number of ions by using the potential shaping capabilities of our segmented ion trap. For single-ion loading, an efficiency of 96.7(7)% has been achieved. These ions are then deterministically extracted out of the trap and focused down to a 1sigma-spot radius of (4.6 \pm 1.3)mum at a distance of 257mm from the trap center. Compared to former measurements without ion optics, the einzel-lens is focusing down the single-ion beam by a factor of 12. Due to the small beam divergence and narrow velocity distribution of our ion source, chromatic and spherical aberration at the einzel-lens is vastly reduced, presenting a promising starting point for focusing single ions on their way to a substrate.Comment: 16 pages, 7 figure

    Microcavity exciton-polariton mediated Raman scattering: Experiments and theory

    Full text link
    We studied the intensity of resonant Raman scattering due to optical phonons in a planar II-VI-type semiconductor microcavity in the regime of strong coupling between light and matter. Two different sets of independent experiments were performed at near outgoing resonance with the middle polariton (MP)branch of the cavity. In the first, the Stokes-shifted photons were kept at exact resonance with the MP, varying the photonic or excitonic character of the polariton. In the second, only the incoming light wavelength was varied, and the resonant profile of the inelastic scattered intensity was studied when the system was tuned out of the resonant condition. Taking some matrix elements as free parameters, both independent experiments are quantitatively described by a model which incorporates lifetime effects in both excitons and photons, and the coupling of the cavity photons to the electron-hole continuum. The model is solved using a Green's function approach which treats the exciton-photon coupling nonperturbatively.Comment: 10 pages, 6 figure

    Magneto-Optical Studies of Exciton Effects in Layer-Type Semiconductors

    Get PDF
    Both experimental and theoretical works were performed with particular reference to a layer-type semiconductor, GaSe, for a coherent treatment of the exciton-like and the oscillatory Landau-like spectra appearing in a form of their combination in semiconductors in magnetic fields. The interband magneto-absorption and the Faraday rotation were measured in pulsed magnetic fields up to ~200 kOe at low temperatures. The theoretical analysis was based mainly on the exact solution for an extremely anisotropic semiconductor in the magnetic field of arbitrary intensity. The exciton effects are discussed in terms of the energy spectrum, the spectral intensity, and the spectral width by the use of the band parameters deduced from the experimental results

    Efficient O(N2)\mathcal{O}(N^2) approach to solve the Bethe-Salpeter equation for excitonic bound states

    Full text link
    Excitonic effects in optical spectra and electron-hole pair excitations are described by solutions of the Bethe-Salpeter equation (BSE) that accounts for the Coulomb interaction of excited electron-hole pairs. Although for the computation of excitonic optical spectra in an extended frequency range efficient methods are available, the determination and analysis of individual exciton states still requires the diagonalization of the electron-hole Hamiltonian H^\hat{H}. We present a numerically efficient approach for the calculation of exciton states with quadratically scaling complexity, which significantly diminishes the computational costs compared to the commonly used cubically scaling direct-diagonalization schemes. The accuracy and performance of this approach is demonstrated by solving the BSE numerically for the Wannier-Mott two-band model in {\bf k} space and the semiconductors MgO and InN. For the convergence with respect to the \vk-point sampling a general trend is identified, which can be used to extrapolate converged results for the binding energies of the lowest bound states.Comment: 13 pages, 12 figures, 1 table, submitted to PR

    Global associations between regional gray matter volume and diverse complex cognitive functions: evidence from a large sample study

    Get PDF
    Correlations between regional gray matter volume (rGMV) and psychometric test scores have been measured to investigate the neural bases for individual differences in complex cognitive abilities (CCAs). However, such studies have yielded different rGMV correlates of the same CCA. Based on the available evidence, we hypothesized that diverse CCAs are all positively but only weakly associated with rGMV in widespread brain areas. To test this hypothesis, we used the data from a large sample of healthy young adults [776 males and 560 females; mean age: 20.8 years, standard deviation (SD) = 0.8] and investigated associations between rGMV and scores on multiple CCA tasks (including non-verbal reasoning, verbal working memory, Stroop interference, and complex processing speed tasks involving spatial cognition and reasoning). Better performance scores on all tasks except non-verbal reasoning were associated with greater rGMV across widespread brain areas. The effect sizes of individual associations were generally low, consistent with our previous studies. The lack of strong correlations between rGMV and specific CCAs, combined with stringent corrections for multiple comparisons, may lead to different and diverse findings in the field

    Refractive error is associated with intracranial volume

    Get PDF
    Myopia is part of the spectrum of refractive error. Myopia is associated with psychometric intelligence and, the link between brain anatomy and myopia has been hypothesized. Here we aimed to identify the associations between brain structures and refractive error in developed young adults. In a study cohort of 1,319 normal educated young adults, the refractive error showed a signifcant negative correlation with total intracranial volume and total cerebrospinal fuid (CSF) volume but not with total gray matter volume (GMV) or total white matter volume (WMV). Time spent studying was associated with refractive error but could not explain the aforementioned associations with brain volume parameters. The R2 values of the simple regression between spherical equivalent and outcome variables for each sex in non-whole brain imaging analyses were less than 0.05 in all cases and thus were weak. Psychometric intelligence was not associated with refractive error or total CSF volume, but it weakly positively correlated with total GMV and total WMV in this study population. Thus, refractive error appears to be primarily (weakly) associated with the volume of the cranium, whereas psychometric intelligence was associated with the volume of the brain
    corecore