Diagnostics of plasma produced by femtosecond laser pulse impact upon a target with an internal nanostructure
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Diagnostics of Plasma Produced by Femtosecond Laser Pulse Impact upon a Target with an Internal Nanostructure I. Yu. Skobeleva, A. Ya. Faenova, S. V. Gasilova, T. A. Pikuza, S. A. Pikuz Jr.a, b, A. I. Magunovc, A. S. Boldarevd, and V. A. Gasilovd a
Joint Institute for High Temperatures, Russian Academy of Sciences, Izhorskaya ul. 13/19, Moscow, 127412 Russia b Moscow Institute of Physics and Technology, Institutskiі per. 9, Dolgoprudnyі, Moscow oblast, 141700 Russia c Prokhorov Institute of General Physics, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 119991 Russia d Institute of Mathematical Modeling, Russian Academy of Sciences, Miusskaya pl. 4a, Moscow, 125047 Russia Received December 11, 2008
Abstract—Xray diagnostics of the interaction of femtosecond laser pulses with intensities of 1016– 1018 W/cm2 with CO2 clusters and frozen nanosize water particles is carried out. The stage of cluster expan sion and the formation of a plasma channel, which governs the parameters of the formed Xray radiation source and accelerated ion flows, is studied. The measurements are based on recording spatially resolved Xray spectra of H and Helike oxygen ions. Utilization of Rydberg transitions for spectra diagnostics makes it possible to determine plasma parameters on a time scale of t ~ 10 ps after the beginning of a femtosecond pulse. The role of the rear edge of the laser pulse in sustaining the plasma temperature at a level of ~100 eV in the stage of a nonadiabatic cluster expansion is shown. The analysis of the profiles and relative intensities of spectral lines allows one to determine the temperature and density of plasma electrons and distinguish the populations of “thermal” ions and ions that are accelerated up to energies of a few tens of kiloelectronvolts. It is shown that the use of solid clusters made of frozen nanoscale water droplets as targets leads to a substan tial increase in the number of fast Helike ions. In this case, however, the efficiency of acceleration of Hlike ions does not increase, because the time of their ionization in plasma exceeds the time of cluster expansion. DOI: 10.1134/S1063780X10130283
1. INTRODUCTION The development of lasers with subpicosecond pulse durations and terawatt intensities has opened up fresh opportunities in investigating the interaction of laser radiation with matter. It is interesting to study both the fundamental problems of high energy density physics and different applied problems, namely the development of efficient sources of Xray radiation based on laser plasma, and the formation of acceler ated charged particle flows. At the same time, the application of different kinds of structured targets, consisting of dense nanoscale clusters (gas clusters [1– 3], snow nanograins [4], and droplets [5]), makes it possible to produce plasma with unique properties. On the one hand, plasma with a density substantially exceeding the critical one, which consists of multi charge ions and electrons with kiloelectronvolt ener gies, is formed in cluste
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