Resonant third harmonic generation of KrF laser in Ar gas

Investigations of emission of harmonics from argon gas jet irradiated by 700 fs, 5 mJ pulses from a KrF laser are presented. Harmonics conversion was optimized by varying the experimental geometry and the nozzle size. For the collection of the harmonic radiation silicon and solar-blind diamond semiconductor detectors equipped with charge preamplifiers were applied. The possibility of using a single-crystal CVD diamond detector for separate measurement of the 3rd harmonic in the presence of a strong pumping radiation was explored. Our experiments show that the earlier suggested 0.7% conversion efficiency can really be obtained, but only in the case when phase matching is optimized with an elongated gas target length corresponding to the length of coherence

Application of laser-induced double ablation of plasma for enhanced macroparticle acceleration

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Progress on lead-free metal halide perovskites for photovoltaic applications: a review

ABSTRACT: Metal halide perovskites have revolutionized the field of solution-processable photovoltaics. Within just a few years, the power conversion efficiencies of perovskite-based solar cells have been improved significantly to over 20%, which makes them now already comparably efficient to silicon-based photovoltaics. This breakthrough in solution-based photovoltaics, however, has the drawback that these high efficiencies can only be obtained with lead-based perovskites and this will arguably be a substantial hurdle for various applications of perovskite-based photovoltaics and their acceptance in society, even though the amounts of lead in the solar cells are low. This fact opened up a new research field on lead-free metal halide perovskites, which is currently remarkably vivid. We took this as incentive to review this emerging research field and discuss possible alternative elements to replace lead in metal halide perovskites and the properties of the corresponding perovskite materials based on recent theoretical and experimental studies. Up to now, tin-based perovskites turned out to be most promising in terms of power conversion efficiency; however, also the toxicity of these tin-based perovskites is argued. In the focus of the research community are other elements as well including germanium, copper, antimony, or bismuth, and the corresponding perovskite compounds are already showing promising properties. GRAPHICAL ABSTRACT: [Image: see text

Neural processing of natural sounds

Natural sounds include animal vocalizations, environmental sounds such as wind, water and fire noises and non-vocal sounds made by animals and humans for communication. These natural sounds have characteristic statistical properties that make them perceptually salient and that drive auditory neurons in optimal regimes for information transmission.Recent advances in statistics and computer sciences have allowed neuro-physiologists to extract the stimulus-response function of complex auditory neurons from responses to natural sounds. These studies have shown a hierarchical processing that leads to the neural detection of progressively more complex natural sound features and have demonstrated the importance of the acoustical and behavioral contexts for the neural responses.High-level auditory neurons have shown to be exquisitely selective for conspecific calls. This fine selectivity could play an important role for species recognition, for vocal learning in songbirds and, in the case of the bats, for the processing of the sounds used in echolocation. Research that investigates how communication sounds are categorized into behaviorally meaningful groups (e.g. call types in animals, words in human speech) remains in its infancy.Animals and humans also excel at separating communication sounds from each other and from background noise. Neurons that detect communication calls in noise have been found but the neural computations involved in sound source separation and natural auditory scene analysis remain overall poorly understood. Thus, future auditory research will have to focus not only on how natural sounds are processed by the auditory system but also on the computations that allow for this processing to occur in natural listening situations.The complexity of the computations needed in the natural hearing task might require a high-dimensional representation provided by ensemble of neurons and the use of natural sounds might be the best solution for understanding the ensemble neural code

Oklusi

viii+354hlm.;25c

K x rays produced in collisions of bare ions with atoms: Contribution of multiple-electron transfer in Kr³⁶⁺, Ar¹⁸⁺, and Ne¹⁰⁺+Ar collisions

K x rays have been observed in low energy collisions of bare Kr, Ar, and Ne ions with a neutral gas target. Although largely neglected previously, we have found that multiple-electron transfer processes play a significant role in shaping the x-ray spectra. The observed ratios of normal-satellite to hyper-satellite line intensities are found to be roughly independent of the ion species and much larger than those estimated from previously reported electron transfer cross sections, suggesting that there may be a strong correlation between two electrons during the electron transfer or during the subsequent cascades. It is suggested that exact knowledge of the initial and final principal and angular momentum quantum numbers (n,l) in electron transfer are the most essential missing ingredients for understanding the entire x-ray emission process in astrophysical, laboratory, and technological plasmas

A Ho3+-Based Luminescent Thermometer for Sensitive Sensing over a Wide Temperature Range

Luminescence thermometry is used in a variety of research fields for noninvasive temperature sensing. Lanthanide-doped micro-/nanocrystals are exceptionally suitable for this. The popular concept of luminescence-intensity-ratio thermometry is based on emission from thermally coupled levels in a single lanthanide ion, following Boltzmann's law. These thermometers can measure temperature with low uncertainty, but only in a limited temperature range. In this work, a Ho3+-based thermometer is presented and quantitatively modeled with sustained low temperature uncertainty from room temperature up to 873 K. The thermometer shows bright green and red luminescence with a strong and opposite dependence on temperature and Ho3+ concentration. This is the result of temperature-dependent competition between multi-phonon relaxation and energy transfer, feeding the green- and red-emitting levels, respectively, following excitation with blue light. This simple and quantitative model of this competition predicts the output spectrum over a wide range of temperatures (300–873 K) and Ho3+ concentrations (0.1–30%). The optimum Ho3+ concentration can thus be determined for reliable measurements over any temperature range of interest. Quantitative modeling as presented here is crucial to optimally benefit from the potential of energy-transfer thermometers to achieve low measurement uncertainties over a wide temperature range