Photoionization experiments with the ultrafast EUV laser 'FLASH' - free electron laser in Hamburg

The advent of mirror-less Free Electron Lasers emitting polarised and coherent 'laser-like' beams of high peak (> 1GW) and average (up to 100mW) powers in the extreme-UV (EUV) and X-ray bands of the electromagnetic spectrum heralds a new era in the study of the photoelectric effect. The unprecedented photon flux (~1013 photons per pulse) opens up to scrutiny processes with cross sections considered hitherto unfeasibly small to probe with conventional EUV sources such as synchrotrons and laser plasmas. The peak intensity of the focussed pulse train (<1013 W/cm2), combined with the high photon energy, ports non-linear optics and spectroscopy into a regime where inner shell electrons can become the predominant mediator of the photon matter interaction. Few photon, few electron photoionization processes are made amenable to study for the first time and the wavelength tunability of the FEL permits resonances to come into play. In combination with ultrafast optical lasers, pump-probe experiments on atoms and molecules where both fields are of comparable high intensity but orders of magnitude different in photon energy become possible. In mid 2005 the 2nd phase of the Free Electron Laser project at DESY, Hamburg (FLASH) opened to users. In what follows I will attempt to illustrate at least some of the impressive progress that has been made by very brief descriptions of just a few of the pathfinder experiments that the growing Atomic and Molecular physics community at FLASH has undertaken in the intervening two years

Tracking ground state Ba+ ions in an expanding laser–plasma plume using time-resolved vacuum ultraviolet photoionization imaging

We report results from a study of the integrated column density and expansion dynamics of ground-state-selected Ba+ ions in a laser–plasma plume using a new experimental system—VPIF (vacuum-ultraviolet photoabsorption imaging facility). The ions are tracked by recording the attenuation of a pulsed and collimated vacuum ultraviolet beam, tuned to the 5p–6d inner-shell resonance of singly ionized barium, as the expanding plasma plume moves across it. The attenuated beam is allowed to fall on a CCD array where the spatial distribution of the absorption is recorded. Time-resolved ion velocity and integrated column density maps are readily extracted from the photoionization images

Emission characteristics and dynamics of the stagnation layer in colliding laser produced plasmas

The expansion dynamics of ion and neutral species in laterally colliding laser produced aluminum plasmas have been investigated using time and space resolved optical emission spectroscopies and spectrally and angularly resolved fast imaging. The emission results highlight a difference in neutral atom and ion distributions in the stagnation layer where, at a time delay of 80 ns, the neutral atoms are localized in the vicinity of the target surface 1 mm from the target surface while singly and doubly charged ions lie predominantly at larger distances, 1.5 and 2 mm, respectively. The imaging results show that the ions were found to form a well defined, but compressed, stagnation layer at the collision front between the two seed plasmas at early times (Dt ~ 80 ns). On the other hand, the excited neutrals were observed to form a V-shaped emission feature at the outer regions of the collision front with enhanced neutral emission in the less dense, cooler regions of the stagnation layer

3p photoabsorption of free and bound Cr, Cr⁺, Mn, and Mn⁺

A dual-laser-plasma technique has been used to measure photoabsorption by atomic Cr and Mn and their ions at photon energies between 40 and 70 eV, where the dominant absorption mechanism is excitation of the 3p subshell. No dramatic differences are observed between the absorption spectra of Mn and Mn+, and these spectra are similar to those of Mn metal and MnCl2. The spectra of Cr and Cr+ are strikingly dissimilar, the mean excitation energy being about 5 eV greater in the ion. We attribute this to strong mixing of the localized 3d6 configuration with 3d5nd Rydberg configurations, an effect that is also responsible for the anomalous appearance of the Cr spectrum with respect to those of the other iron-period elements. The absorption spectra of Cr metal and CrCl2 take forms intermediate between those of Cr and Cr+. We give spectroscopic assignments to most of the sharp absorption features of Cr+ and determine the 3p ionization thresholds from quantum-defect analysis

Video-Assisted Thoracoscopy in the Management of Primary and Secondary Pneumothorax

The management of primary and secondary spontaneous pneumothorax can have many variations depending on the surgeons and their expertise of practice. The end goal is to stop the recurrence. The history of treatment, clinical indications for surgery, and preoperative and postoperative decision-making for intervention are summarized. Surgical intervention plays an important role in the management of recurrent pneumothorax and complex initial pneumothorax. Over the years the surgical techniques have evolved, and currently, video-assisted thoracoscopic techniques are frequently used in the management. In this concise report, we attempt to analyze the surgical techniques currently in use and their outcomes. Furthermore, we attempt to integrate future innovations in the management of this common disorder

4p-inner-shell and double-excitation spectrum of Sr II

We report photoabsorption measurements from the 4p inner shell of singly ionized strontium in the spectral region between 26.0 and 37.4 eV. More than 60 levels of Sr II are reported which are interpreted as singly excited inner-shell transitions 4p65s 2S1∕2→4p45s(1P,3P)ns, md and doubly excited transitions 4p65s 2S1∕2→4p54d(1P,3P,3D)nl. Multiconfiguration Hartree-Fock calculations are performed in jj coupling and the levels are arranged into Rydberg series converging on seven limits, allowing the identification of two levels in Sr III

Larval culture of the calico scallop, Argopecten gibbus

Mature calico scallops, Argopecten gibbus, collected from the grounds off Cape Kennedy, Florida, were induced to spawn in the laboratory. Fertilized eggs were reared to postlarvae in sea water of 23° C ± 2.0° C at a salinity of 35 %o. The external morphology of eggs and developing larval stages are described

Not all biodiversity rich spots are climate refugia

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