ABSTRACT
We demonstrate the three-fold post-chirped-pulse-amplification (post-CPA) pulse compression of a high peak power laser pulse using allyl diglycol carbonate (CR39), which was selected as the optimal material for near-field self-phase modulation out of a set of various nonlinear plastic materials, each characterized with respect to its nonlinear refractive index and optical transmission. The investigated materials could be applied for further pulse compression at high peak powers, as well as for gain narrowing compensation within millijoule-class amplifiers. The post-CPA pulse compression technique was tested directly after the first CPA stage within the POLARIS laser system, with the compact setup containing a single 1 mm thick plastic sample and a chirped mirror pair, which enabled a substantial shortening of the compressed pulse duration and, hence, a significant increase in the laser peak power without any additional modifications to the existing CPA chain.
ABSTRACT
We report on the successful implementation and characterization of a cryogenic solid hydrogen target in experiments on high-power laser-driven proton acceleration. When irradiating a solid hydrogen filament of 10 µm diameter with 10-Terawatt laser pulses of 2.5 J energy, protons with kinetic energies in excess of 20 MeV exhibiting non-thermal features in their spectrum were observed. The protons were emitted into a large solid angle reaching a total conversion efficiency of several percent. Two-dimensional particle-in-cell simulations confirm our results indicating that the spectral modulations are caused by collisionless shocks launched from the surface of the the high-density filament into a low-density corona surrounding the target. The use of solid hydrogen targets may significantly improve the prospects of laser-accelerated proton pulses for future applications.
ABSTRACT
Yb(3+)-doped gain media offer favorable properties for diode-pumped laser amplifiers for high-energy ns-pulses. To reach high optical-to-optical conversion efficiencies at room temperature however, very high and often impractical fluences are required both for pumping and extraction. Low temperature operation offers a solution, but the required cryogenic cooling systems add considerable complexity, bulkiness and cost. Multi-passing both pump and extraction beams through the gain medium is an alternative approach to overcome efficiency limitations at room temperature. In this article we present numerical and experimental results to this effect.We demonstrated ns-pulse output from a diode-pumped Yb:YAG amplifier at an energy of 566 mJ and an optical-to-optical efficiency of 20%, which is almost a doubling of the efficiency achieved with ns-lasers employing Yb(3+)-doped gain media at this energy level.
Subject(s)
Aluminum , Yttrium , Computer-Aided Design , Energy Transfer , Equipment Design , Equipment Failure Analysis , Reproducibility of Results , Sensitivity and Specificity , TemperatureABSTRACT
15-Lipoxygenase is implicated in the selective breakdown of mitochondria during red cell maturation by virtue of its capability of directly oxygenating phospholipids. To address the reason of the selectivity for mitochondria, we studied the reaction of pure rabbit 15-lipoxygenase with beef heart submitochondrial particles in vitro. This reaction is characterised by a loss of polyenoic fatty acids, the formation of phospholipid-bound hydroperoxy- and keto-polyenoic fatty acids, and oxidative modification of membrane proteins. The total oxygen uptake exceeds the formation of oxygenated polyenoic fatty acids several times. The excessive oxygen uptake was not inhibited by 3,5-di-tert-butyl-4-hydroxytoluene or by respiratory inhibitors, but was partly suppressed by superoxide dismutase plus catalase, salicylate, or mannitol. Pentane-extraction of the submitochondrial particles abolished the excessive oxygen uptake, whereas reconstitution with ubiquinone- 50 restored it. A marked excessive oxygen uptake did not occur during the analogous reaction with erythrocyte ghosts. It is proposed that ubiquinone-50 triggers the formation of hydroxyl radicals from 15-lipoxygenase-derived hydroperoxy-lipids via a Fenton-type reaction driven by ubisemiquinone radicals. A new prooxidative function of ubiquinone in the biologically programmed degradation of mitochondria in certain types of cells is proposed.
Subject(s)
Arachidonate 15-Lipoxygenase/metabolism , Arachidonate 15-Lipoxygenase/pharmacology , Cell Membrane/metabolism , Oxygen/metabolism , Amino Acids/analysis , Animals , Cattle , Cell Membrane/chemistry , Chromatography, High Pressure Liquid , Electron Transport/physiology , Electrophoresis, Gel, Two-Dimensional , Erythrocytes/enzymology , Fatty Acids, Unsaturated/chemistry , Fatty Acids, Unsaturated/metabolism , Free Radicals/metabolism , Keto Acids/metabolism , Lipid Peroxidation , Mammals/metabolism , Mitochondria, Heart/metabolism , Models, Chemical , Multienzyme Complexes/antagonists & inhibitors , Multienzyme Complexes/metabolism , NADH, NADPH Oxidoreductases/antagonists & inhibitors , NADH, NADPH Oxidoreductases/metabolism , Rabbits , Succinate Dehydrogenase/antagonists & inhibitors , Succinate Dehydrogenase/metabolism , Ubiquinone/metabolism , Vitamin E/analysis , Vitamin E/metabolismABSTRACT
Lipoxygenase catalysed reactions play an important role in the field of lipid peroxidation. The enzyme is characterized concerning its sources, biological importance, isolation, substrates, active centre and inhibition. Extensive explanations should show the complex mechanisms of enzyme catalyses divided into two major ways: dioxygenase and hydroperoxidase reactions. Food science specific importance and expected effects on food systems are discussed and related to reaction products generated during catalysis and enzymatic processes both preceding and following lipoxygenase reaction.
