Nanocluster-induced quantum photoyield of metal alloy systems

In order to find the origin of photoemission and increase the low quantum yield (QY) suitable metals such as magnesium and aluminium, a correlation between the QY in the UV-spectrum range and the electron density of states (DOS) near the Fermi level is considered for light metal alloy systems by using the data of UV-photoelectron spectroscopy, volume paramagnetic susceptibility, and HRTEM studies. The spectral responses of the photoyield for the HCP Mg–Ba alloys are proven to be in agreement with Fowler’s law for a near-free-electron model. The Mg₁₆Ba₂ bimetallic nanocluster-induced distribution of the DOS, calculated by the ab initio FLAPW method near the Fermi level closely resembles that obtained by the UV-photoelectron spectroscopy in the bulk Mg–2% Ba alloy. It means that a substantial increase in the DOS near the Fermi level is caused by the electron structure of the cluster to be formed. These metallic-like nanoclusters of 8 nm in diameter embedded in the bulk of extended solid solution crystals act as new and much more efficient photoemission centers and insure a drastic increase in the QY of the massive magnesium photocathode by several orders of magnitude. The new approach is applicable to similar metal alloy systems such as the FCC Al–Li, Ba as regards their treatment on the basis of the physical principles of small-scale alloying with emission-active and cluster-forming additives.     

Second-harmonic generation and wave-front correction of a terawatt laser system

By combining second-harmonic generation and wave-front correction of a hybrid Ti:sapphire-Nd:glass terawatt laser chain, we were able to generate a focused intensity above 10(19) W/cm(2), with an estimated 10(9):1 intensity contrast ratio. The frequency of the laser is doubled by use of a type I KDP crystal, and wave-front correction is achieved with a deformable mirror coupled to a wave-front sensor.     

Control of energy spread and dark current in proton and ion beams generated in high-contrast laser solid interactions

By using temporal pulse shaping of high-contrast, short pulse laser interactions with solid density targets at intensities of 2 × 10(21) W cm(-2) at a 45° incident angle, we show that it is possible to reproducibly generate quasimonoenergetic proton and ion energy spectra. The presence of a short pulse prepulse 33 ps prior to the main pulse produced proton spectra with an energy spread between 25% and 60% (ΔE/E) with energy of several MeV, with light ions becoming quasimonoenergetic for 50 nm targets. When the prepulse was removed, the energy spectra was broad. Numerical simulations suggest that expansion of the rear-side contaminant layer allowed for density conditions that prevented the protons from being screened from the sheath field, thus providing a low energy cutoff in the observed spectra normal to the target surface.     

High-power, kilojoule class laser channeling in millimeter-scale underdense plasma

Experiments were performed using the Omega EP laser, operating at 740 J of energy in 8 ps (90 TW), which provides extreme conditions relevant to fast ignition studies. A carbon and hydrogen plasma plume was used as the underdense target and the interaction of the laser pulse propagating and channeling through the plasma was imaged using proton radiography. The early time expansion, channel evolution, filamentation, and self-correction of the channel was measured on a single shot via this method. A channel wall modulation was observed and attributed to surface waves. After around 50 ps, the channel had evolved to show bubblelike structures, which may be due to postsoliton remnants.     

Temperature-dependent segregation of Pr3+ impurity ions in Y2SiO5:Pr3+ and YPO4:Pr3+ nanocrystals

Stationary and time-resolved spectroscopic methods are used to show that the impurity ions in Y₂SiO₅:Pr³⁺ and YPO₄:Pr³⁺ nanocrystals are distributed nonuniformly. This nonuniform distribution is found to be caused by the temperature-dependent segregation of Pr³⁺ ions near the surface of a nanocrystal. The motion of the activator ions from the bulk of a nanocrystal to the near-surface layer is traced when the activator concentration and the heat-treatment parameters are varied over wide ranges, and the main parameters of this effect (impurity redistribution intensity and time, diffusion coefficient) are estimated.     

Trigger System of the HyperNIS Experiment

Physics of Particles and Nuclei Letters - The trigger system of the HyperNIS spectrometer, which was proposed for distinguishing events with the formation and subsequent decay of relativistic...     

The shear modulus of the human vocal fold in a transverse direction

The aim of this study was to measure the shear modulus of the vocal fold in a human hemilarynx, such that the data can be related to direction of applied stress and anatomical context. Dynamic spring rate data were collected using a modified linear skin rheometer using human hemilarynges, and converted to estimated shear modulus via application of a simple shear model. The measurement probe was attached to the epithelial layer of the vocal fold cover using suction. A sinusoidal force of 3g was applied to the epithelium, and the resultant displacement logged at a rate of 1kHz. Force measurement accuracy was 20microg and position measurement accuracy was 4microm. The force was applied in a transverse direction at the midmembranous point between the vocal process and the anterior commissure. The shear modulus of the three female vocal folds ranged from 814 to 1232Pa. The shear modulus of the three male vocal folds ranged from 1021 to 1796Pa. These data demonstrate that it is possible to obtain estimates for the shear modulus of the vocal fold while preserving anatomical context. The modulus values reported here are higher than those reported using parallel plate rheometry. This is to be expected as the tissue is attached to surrounding structures, and is under natural tension.     

Demonstration of fiber-laser-produced plasma source and application to efficient extreme UV light generation

Efficient generation of extreme UV (EUV) light at lambda = 13.5 nm from a bulk Sn target has been demonstrated by using a fiber laser. The conversion efficiency from the 1064 nm IR to the EUV was measured to be around 0.9% into 2pi steradians within a 2% bandwidth. To the best of our knowledge, this is the first time an all-fiber system was used to generate EUV or soft x rays.     

Cyclohexane selective oxidation over metal-organic frameworks of MIL-101 family: superior catalytic activity and selectivity

Mesoporous metal-organic frameworks Cr- and Fe-MIL-101 are highly efficient, true heterogeneous and recyclable catalysts for solvent-free selective oxidation of cyclohexane with molecular oxygen and/or tert-butyl hydroperoxide under mild conditions.     

Observation of the plasma channel dynamics and Coulomb explosion in the interaction of a high-intensity laser pulse with a He gas jet

We report the first interferometric observations of the dynamics of electron-ion cavitation of relativistically self-focused intense 4 TW, 400 fs laser pulse in a He gas jet. The electron density in a channel 1 mm long and 30 μm in diameter drops by a factor of approximately 10 from the maximum value of ∼8×10¹⁹ cm⁻³. A high radial velocity of the plasma expansion, ∼3.8×10⁸ cm/s, corresponding to an ion energy of about 300 keV, is observed. The total energy of fast ions is estimated to be 6% of the laser pulse energy. The high-velocity radial plasma expulsion is explained by a charge separation due to the strong ponderomotive force. This experiment demonstrates a new possibility for direct transmission of a significant portion of the energy of a laser pulse to ions. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 12, 787–792 (25 December 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.