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This study is devoted to the high-energy X-ray radiography investigation on the ejecta physics of laser shock-loaded tin. The ejecta were generated via laser shock loaded tin under sequential shock-breakout pressures by high-power nanosecond lasers. A high-energy X-ray (50∼200keV) source was created to radiograph the high dense ejecta. Due to its strong penetration, high-quality radiograph images were obtained with detailed inner information and topology structure of ejecta. The areal density distribution and total mass of ejecta were further inferred. It was found that the ejecta from laser shock-loaded tin under sequential pressures show obvious difference in density distribution between the samples in a solid state and in a melt-on-release state. In addition, the total mass of ejecta was demonstrated to increase sharply when the breakout pressure is larger than the onset of melt-on-release for tin. Such increase inferred a solid-liquid phase transition of ejecta production mechanism. [ABSTRACT FROM AUTHOR]

An ultraintense femtosecond laser pulse was used, for the first time, to produce a strong magnetic field with controlled shapes by interactions with a capacitor-coil target with high efficiency. The temporal evolution of the strong magnetic field was obtained by the time-gated proton radiography method. A comparison of high-resolution radiographic images of proton deflection and particle-track simulations indicates a peak magnetic field of ∼20 T. The energy conversion efficiency from the ultraintense laser pulse to the magnetic field is as high as ∼10%. A simple model of the ultraintense laser-driven capacitor-coil target gives a relationship between the magnetic field strength and the electron temperature produced by the laser. Our results indicate that magnetic fields of tens of tesla could be stably produced by most of the existing ultraintense laser facilities. It potentially opens new frontiers in basic physics which require strong magnetic field environments. [ABSTRACT FROM AUTHOR]

For high-energy gain of electron acceleration by a laser wakefield, a stable or guiding propagation of an ultrashort, high-intensity laser pulse in a gas-target plasma is of fundamental importance. Preliminary experiments were carried out for the propagation of 30-fs, ~100-TW laser pulses of intensities ~1019W/cm2 in plasma of densities ~1019/cm3. Self-guiding length of nearly 1.4 mm was observed in a gas jet and 15 mm in a hydrogen-filled capillary. Fluid-dynamics simulations are used to characterize the two types of gas targets. Particle-in-cell simulations indicate that in the plasma, after the pulse's evolution of self-focusing and over-focusing, the high-intensity pulse could be stably guided with a beam radius close to the plasma wavelength. At lower plasma densities, a preformed plasma channel of a parabolic density profile matched to the laser spot size would be efficient for guiding the pulse. [ABSTRACT FROM PUBLISHER]

The spectrum of laser–plasma generated X-rays is very important, it characterizes electron dynamics in plasma and is basic for applications. However, the accuracies and efficiencies of existing methods to diagnose the spectrum of laser–plasma based X-ray pulse are not very high, especially in the range of several hundred keV. In this study, a new method based on electron tracks detection to measure the spectrum of laser–plasma produced X-ray pulses is proposed and demonstrated. Laser–plasma generated X-rays are scattered in a multi-pixel silicon tracker. Energies and scattering directions of Compton electrons can be extracted from the response of the detector, and then the spectrum of X-rays can be reconstructed. Simulations indicate that the energy resolution of this method is approximately 20% for X-rays from 200 to 550 keV for a silicon-on-insulator pixel detector with 12 μ m pixel pitch and 500 μ m depletion region thickness. The results of a proof-of-principle experiment based on a Timepix3 detector are also shown. [ABSTRACT FROM AUTHOR]