Characterization of preformed plasmas with an interferometer for ultra-short high-intensity laser-plasma interactions

The evolution of an Al preformed plasma produced by a prepulse was observed before and after the arrival of the main pulse by an interferometer using a femtosecond probe pulse. A central density depression due to the ponderomotive force of the main laser pulse in the preformed plasma with a 100 m scale length was clearly visible after the main pulse irradiation at an intensity of 5×10¹⁶ W/cm². The temporal profiles of the prepulse, characterized by a cross-correlation in conjunction with a precise density profile measurement by an interferometer, contribute to the better understanding of femtosecond laser-matter interactions. PACS 52.38.-r; 52.50.Jm; 52.70.-m     

A novel chelatofore functionalized spiropyran of the 2‐oxaindane series

A novel chelatofore functionalized spiropyran of the 2‐oxaindane series, namely 8‐formyl‐7‐hydroxy‐3′,3′‐dimethylspiro[2H‐chromene‐2,1′(3′H)‐2‐benzofuran], C₁₉H₁₆O₄, is reported. In the crystalline state, dimers are formed as a result of the π–π stacking of aromatic groups of the 2H‐chromene part of the molecule and C—H...O interactions. The C_spiro—O bond length in the pyran ring is 1.4558 (10) Å, which is longer than or equal to the bond length in thermo‐ and photochromic 2‐oxaindane spiropyrans synthesized previously, except for the 7,8‐benzo/6‐NO₂ derivative, in which this bond length is 1.465 (2) Å.     

Reaction of silicon tetrafluoride with calcium hydride as a propagating wave

The synthesis of silane by reacting silicon tetrafluoride and calcium hydride is shown to proceed as a propagating wave. The main parameters of the process, namely, the propagation velocity, the reaction front temperature, and calcium conversion, are determined. The mathematical model of wave propagation for an exothermic reaction in a porous medium with purging a gaseous oxidant describes qualitatively the major laws of the process.     

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.     

Determination of Impurity Arsenic in High-Purity Sulfur by Electrothermal Atomic-Absorption Spectrometry with the Use of Solvent Extraction

A procedure was developed for determining impurity arsenic in high-purity sulfur with a detection limit of 1 × 10^–7 wt %. The samples of sulfur to be studied were dissolved in nitric acid in an autoclave, and then the arsenic impurity was extracted with toluene and back-extracted with distilled water. Arsenic was determined in the back-extract by electrothermal atomic-absorption spectrometry.     

Stability of a plasma foil in the radiation pressure dominated regime

The stability of a thin plasma foil accelerated to relativistic velocities by the radiation pressure of an ultra high intensity electromagnetic pulse is investigated. The effects of the onset of a Rayleigh-Taylor-like instability are discussed in the context of the ion acceleration process during the interaction of the laser pulse with the plasma. It is stressed that the experimental study of this advanced laser plasma interaction regime will be accessible within the framework of the ELI experiment and will be of relevance for our understanding of high energy astrophysical phenomena.     

Synthesis of High-Purity Calcium Hydride

A procedure for synthesizing high-purity calcium hydride in high yield was suggested. The admixture composition of the resulting CaH₂ was determined by laser mass spectrometry.     

Demonstration of laser-frequency upshift by electron-density modulations in a plasma wakefield

In a plasma wake wave generated by a high power laser, modulations of the electron density take the shape of paraboloidal dense shells, moving almost at the speed of light. A counterpropagating laser pulse is partially reflected from the shells, acting as relativistic flying mirrors, producing a time-compressed frequency-multiplied pulse due to the double Doppler effect. The counterpropagating laser pulse reflection from the plasma wake wave accompanied by its frequency multiplication (with a factor from 50 to 114) was detected in our experiment.     

Photon bubbles and ion acceleration in a plasma dominated by the radiation pressure of an electromagnetic pulse

The stability of a thin plasma foil accelerated by the radiation pressure of a high intensity electromagnetic (e.m.) pulse is investigated analytically and with particle in cell numerical simulations. It is shown that the onset of a Rayleigh-Taylor-like instability can lead to transverse bunching of the foil and to broadening of the energy spectrum of fast ions. The use of a properly tailored e.m. pulse with a sharp intensity rise can stabilize the foil acceleration.     

Novel hydrazone derivatives of 7‐hydroxy‐3′,3′‐dimethyl‐3′H‐spiro[chromene‐2,1′‐isobenzofuran]‐8‐carbaldehyde

The structures of new oxaindane spiropyrans derived from 7‐hydroxy‐3′,3′‐dimethyl‐3′H‐spiro[chromene‐2,1′‐isobenzofuran]‐8‐carbaldehyde (SP1), namely N‐benzyl‐2‐[(7‐hydroxy‐3′,3′‐dimethyl‐3′H‐spiro[chromene‐2,1′‐isobenzofuran]‐8‐yl)methylidene]hydrazinecarbothioamide, C₂₇H₂₅N₃O₃S, (I), at 120 (2) K, and N′‐[(7‐hydroxy‐3′,3′‐dimethyl‐3′H‐spiro[chromene‐2,1′‐isobenzofuran]‐8‐yl)methylidene]‐4‐methylbenzohydrazide acetone monosolvate, C₂₇H₂₄N₂O₄·C₃H₆O, (II), at 100 (2) K, are reported. The photochromically active C_spiro—O bond length in (I) is close to that in the parent compound (SP1), and in (II) it is shorter. In (I), centrosymmetric pairs of molecules are bound by two equivalent N—H...S hydrogen bonds, forming an eight‐membered ring with two donors and two acceptors.