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

The Efficiency Gains from Fully Delineating Rights in an ITQ Fishery

Individual transferable quota (ITQ) regulation relies on a decentralized market mechanism and a single price to allocate access to a stock of fish. The resulting allocation will not be fully efficient if the stock being allocated is heterogeneous or if there are potential gains from centralized coordination of harvesting effort. If stocks are heterogeneous in their density, location, or unit value during the season, harvesters governed by an ITQ policy will not be indifferent to when or where they exercise their quotas. Stocks that are relatively dense and/or close to port will be preferred to those less dense or more remote. Because an ITQ policy assigns the same opportunity cost for each unit harvested, individual harvesters have an incentive to compete for higher-valued units, and such competition may dissipate part of the fishery’s potential rent. A similar phenomenon arises when stock densities vary in an unknown way over space or time, so harvesters must engage in costly search. Individual harvesters governed by an ITQ policy still face a collective action problem which limits the incentive to share information on stock locations. This can lead to redundant search effort. We demonstrate that both sources of inefficiency can be eliminated either by defining ITQ rights more precisely or by an agreement among harvesters to coordinate their effort. We develop models that illustrate these effects and identify the factors that determine their likely size. Anecdotal evidence on practices adopted by fishery cooperatives is presented to illustrate the practical relevance of the issues we raise.ITQ fishery, cooperative, search, game theory, property rights, Environmental Economics and Policy, Institutional and Behavioral Economics, International Relations/Trade, Q22, D23, K11,

Features in the ion emission of Cu, Al, and C plasmas produced by ultrafast laser ablation

© 2015 AIP Publishing LLC. The bi-modal nature of charge integrated ion kinetic energy distributions, which result from ultrafast laser produced plasmas, is discussed in this paper. A negatively biased Faraday cup was used as a charge collector to measure ion distributions from three different solid targets that had been irradiated with an ultrafast laser in the fluence range 0.1-1 J/cm2. A bi-modal time of flight distribution is found for all three targets (C, Al, and Cu). In the case of the metallic targets (Al and Cu), high- and low-kinetic energy peaks exhibit quite different dependencies on laser fluence, whereas for the semi-metallic target (C), both peaks scale similarly with ultrafast laser fluence. The results are discussed within the framework of a one dimensional capacitor model resulting in ion acceleration

Permanence analysis of a concatenated coding scheme for error control

A concatenated coding scheme for error control in data communications is analyzed. In this scheme, the inner code is used for both error correction and detection, however, the outer code is used only for error detection. A retransmission is requested if the outer code detects the presence of errors after the inner code decoding. Probability of undetected error is derived and bounded. A particular example, proposed for the planetary program, is analyzed

The DCU laser ion source

Laser ion sources are used to generate and deliver highly charged ions of various masses and energies. We present details on the design and basic parameters of the DCU laser ion source (LIS). The theoretical aspects of a high voltage (HV) linear LIS are presented and the main issues surrounding laser-plasma formation, ion extraction and modeling of beam transport in relation to the operation of a LIS are detailed. A range of laser power densities (I ∼ 108–1011 W cm−2) and fluences (F = 0.1–3.9 kJ cm−2) from a Q-switched ruby laser (full-width half-maximum pulse duration ∼ 35 ns, λ = 694 nm) were used to generate a copper plasma. In “basic operating mode,” laser generated plasma ions are electrostatically accelerated using a dc HV bias (5–18 kV). A traditional einzel electrostatic lens system is utilized to transport and collimate the extracted ion beam for detection via a Faraday cup. Peak currents of up to I ∼ 600 μA for Cu+ to Cu3+ ions were recorded. The maximum collected charge reached 94 pC (Cu2+). Hydrodynamic simulations and ion probe diagnostics were used to study the plasma plume within the extraction gap. The system measured performance and electrodynamic simulations indicated that the use of a short field-free (L = 48 mm) region results in rapid expansion of the injected ion beam in the drift tube. This severely limits the efficiency of the electrostatic lens system and consequently the sources performance. Simulations of ion beam dynamics in a “continuous einzel array” were performed and experimentally verified to counter the strong space-charge force present in the ion beam which results from plasma extraction close to the target surface. Ion beam acceleration and injection thus occur at “high pressure.” In “enhanced operating mode,” peak currents of 3.26 mA (Cu2+) were recorded. The collected currents of more highly charged ions (Cu4+–Cu6+) increased considerably in this mode of operation

Quality versus Quantity: An Investigation into Electronic Word of Mouth’s Influence on Consumer Buying Intention

Online consumer reviews play an increasingly crucial role in shaping purchasing intention. With the wide-spread reviews available around the world on sites like TripAdvisor or Yelp, companies’ reputation and hence survival are potentially at risk. The purpose of this study is to investigate the impacts of electronic word-of-mouth (eWOM) on the individual’s attitudes towards the quantity and quality of online store reviews and consider how it impacts their behavior. We incorporate brand trust as a mediator in the relationship between eWOM and purchase intention. Using a vignette survey experiment centered on coffee shop reviews in Hanoi, Vietnam, we test our hypothesis with 223 respondents. Results showed that the number and quality of review does significantly affect purchase intention. Findings also show that brand trust has a mediating effect on the relationship between online reviews and buying intention. This study assists practitioners to develop user-oriented information review format in order to manage online consumer reviews properly and effectively

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