D. Cubaynes

Femtosecond x-ray pulse length characterization at the Linac Coherent Light Source free-electron laser

Two-color, single-shot time-of-flight electron spectroscopy of atomic neon was employed at the Linac Coherent Light Source (LCLS) to measure laser-assisted Auger decay in the x-ray regime. This x-ray-optical cross-correlation technique provides a straightforward, non-invasive and on-line means of determining the duration of femtosecond (>40?fs) x-ray pulses. In combination with a theoretical model of the process based on the soft-photon approximation, we were able to obtain the LCLS pulse duration and to extract a mean value of the temporal jitter between the optical pulses from a synchronized Ti-sapphire laser and x-ray pulses from the LCLS. We find that the experimentally determined values are systematically smaller than the length of the electron bunches. Nominal electron pulse durations of 175 and 75?fs, as provided by the LCLS control system, yield x-ray pulse shapes of 120?20?fs full-width at half-maximum (FWHM) and an upper limit of 40?20?fs FWHM, respectively. Simulations of the free-electron laser agree well with the experimental results.

Photoionization study of Kr+ and Xe+ ions with the combined use of a merged-beam set-up and an ion trap

Photoionization cross sections of halogen-like Kr+ and Xe+ ions have been measured in the photon energy range extending up to 15 eV above the threshold. Two different devices were used, a merged-beam set-up and an ion trap. Combination of the two techniques allows for the extraction of the pure ground state ionization cross section on an absolute scale. Multiconfiguration Dirac–Fock calculations reproduce the magnitude of the direct photoionization cross sections well.

K-shell photoionization of B-like atomic nitrogen ions: experiment and theory

Measurements of absolute cross sections for the K-shell photoionization of B-like atomic nitrogen ions were carried out utilizing the ion?photon merged-beam technique at the SOLEIL synchrotron radiation facility in Saint-Aubin, France. High-resolution spectroscopy with E/?E ?13,500 was the maximum resolution achieved. We have investigated two photon energy regions: 404?409?eV and 439?442?eV. Resonance peaks found in the experimental measured cross sections are compared with theoretical estimates from the multi-configuration Dirac?Fock, R-matrix and empirical methods, allowing identification of the strong 1s ? 2p and the weaker 1s ? 3p resonances in the observed K-shell spectra of this B-like nitrogen ion.

MEASUREMENTS AND CALCULATIONS OF PHOTOIONIZATION CROSS SECTIONS OF MULTIPLY CHARGED IONS IN GROUND AND METASTABLE STATES ALONG THE ISONUCLEAR SERIES OF OXYGEN: O^2^+ TO O^4^+

In this paper, we present the first absolute measurements for photoionization of multiply charged oxygen ions: O 2+ and O 3+ in the ground state and in several metastable states, as well as relative data for O 4+ . Multiconfiguration Dirac-Fock and relativistic R-matrix calculations were performed and are tested here by comparison with experimental results. Our experimental and new theoretical results are also compared with the earlier theoretical data obtained in the R-matrix approximation to calculate photoionization cross sections over part of the isonuclear series of multiply charged oxygen ions. Subject headings: atomic data — methods: laboratory

NEW HIGH-RESOLUTION MEASUREMENTS OF DOUBLY EXCITED STATES OF LI+

We present new results for the doubly excited states Li+(nln´l´) of singly ionized lithium which arise from the measurements of the Auger decay of these states to Li++ ground state ions. Primary excitation of the doubly excited states is achieved by photon impact on neutral lithium atoms and therefore the experiment probes directly the double-shakeup photoionization process h+LiLi+**+e-. Detection of the individual Li+ Auger decay lines provides information on the energies and widths of many doubly excited levels of the ion, including the lowest lying (3l,3l´) state. Classifications are made using recent theoretical calculations.

K-shell photoionization of Be-like and Li-like ions of atomic nitrogen: experiment and theory

Absolute cross sections for the K-shell photoionization of Be-like and Li-like atomic nitrogen ions were measured by employing the ion?photon merged-beam technique at the SOLEIL synchrotron radiation facility in Saint-Aubin, France. High-resolution spectroscopy at nominal resolutions of 38, 56, 111, 133 meV full width at half maximum (FWHM) for Be-like and 125 meV FWHM for Li-like atomic nitrogen ions was achieved for the photon energies ranging from 410 up to 460?eV. The experimental measurements are compared with theoretical estimates from the multi-configuration Dirac?Fock, R-matrix and an empirical method. The interplay between experiment and theory enabled the identification and characterization of the strong 1s ? 2p resonances features observed in the K-shell spectra of each ion and the region around 460?eV for the 1s ? 3p resonance of the N3 + ion yielding suitable agreement with experiment.

K-shell photoionization of B-like oxygen (O3 +) ions: experiment and theory

Absolute cross sections for the {\it K}-shell photoionization of boron-like (B-like) O

Recent results on the photoionisation of multiply-charged ions

^{3+}

Complete description of 3p photoionization in calcium

ions were measured by employing the ion-photon merged-beam technique at the SOLEIL synchrotron-radiation facility in Saint-Aubin, France. High-resolution spectroscopy with E/

Hollow-atom - hollow-ion decay routes of triply excited lithium: first Auger results and a comparison with R-matrix calculations

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