1063-7761/02/9401- $22.00 © 2002 MAIK “Nauka/Interperiodica” 0060 Journal of Experimental and Theoretical Physics, Vol. 94, No. 1, 2002, pp. 60–72. From Zhurnal Éksperimental’noœ i Teoreticheskoœ Fiziki, Vol. 121, No. 1, 2002, pp. 73–87. Original English Text Copyright © 2002 by Rosmej, Hoffmann, Süß, Stepanov, Satov, Smakovskii, Roerich, Khomenko, Makarov, Starostin, Faenov, Skobelev, Magunov, Geißel, Pirzadeh, Seelig, Pikuz, Bock, Letardi, Flora, Bollanti, Di Lazzaro, Reale, Scafati, Tomassetti, Auguste, d’Oliveira, Hulin, Monot, Sharkov. 1. INTRODUCTION The interaction of intense laser radiation with matter leads to the creation of plasma in which the absorbed energy is not completely thermalized. This gives rise to the familiar phenomena of fast ion emission, whose understanding is important for both laser fusion and development of fast ion sources [1–3]. Until now, the main part of the experimental infor- mation on the fast ion production in laser plasmas was obtained with the help of mass spectrometry methods (see, e.g., review [4] and the special issue [5]). These methods are based on the direct observation of ions over large distances, usually performed by charged par- ticle detectors (e.g., Faraday detector) several meters away from the place of plasma creation. In this case, the results strongly depend on the recombination processes that occur during the plasma expansion to large dis- tances. Thus, although these methods are suitable to investigate laser-produced plasmas as possible sources of multicharged fast ions for some practical applica- tions, they have serious limitations for studies of the fast ion production mechanisms inside the laser-pro- duced plasma. More suitable for this purpose are indi- rect spectroscopic methods—the observation of pho- tons emitted by fast ions rather than the direct observa- tion of fast ions. At present, such spectroscopic methods are not widely used for the investigations of fast ions. There are only several papers where these methods have been used in nanosecond [6–8] and fem- tosecond [9, 10] laser-produced plasmas. The Generation of Fast Particles in Plasmas Created by Laser Pulses with Different Wavelengths ¶ F. B. Rosmej 1 , D. H. H. Hoffmann 1 , W. Süß 1 , A. E. Stepanov 2 , Yu. A. Satov 2 , Yu. B. Smakovskii 2 , V. K. Roerich 2 , S. V. Khomenko 2 , K. N. Makarov 2 , A. N. Starostin 2 , A. Ya. Faenov 3 , I. Yu. Skobelev 3, *, A. I. Magunov 3 , M. Geißel 4 , P. Pirzadeh 4 , W. Seelig 4 , T. A. Pikuz 5 , R. Bock 6 , T. Letardi 7 , F. Flora 7 , S. Bollanti 7 , P. Di Lazzaro 7 , A. Reale 8 , A. Scafati 8 , G. Tomassetti 8 , T. Auguste 9 , P. d’Oliveira 9 , S. Hulin 9 , P. Monot 9 , and B. Yu. Sharkov 10 1 Technische Universität Darmstadt, Institut für Kernphysik, Abt. Strahlen- und Kernphysik, D-64289, Darmstadt, Germany 2 Troitsk Institute of Innovative and Thermonuclear Research (TRINITI), Moscow, 142092 Russia 3 Multicharged Ions Spectra Data Center of VNIIFTRI, Mendeleevo, Moscow oblast, 141570 Russia 4 Technische Universität Darmstadt, Institut für Angewandte Physik, D-64289, Darmstadt, Germany 5 Bauman Moscow State Technical University, Moscow, 107005 Russia 6 Gesellschaft für Schwerionenforschung, Plasmaphysics, D-64291, Darmstadt, Germany 7 Dipartimento Innovazione, CR ENEA, Frascati, Italy 8 Dipartimento di Fisica e INFM, INFN g.e. LNGS, Università de L’Aquila, 67010, L’Aquila, Italy 9 Centre d’Etudes de Saclay, DSM/DRECAM/SPAM, Bat ˆ 52291191, Gif-sur-Yvette, Cédex, France 10 Institute of Theoretical and Experimental Physics, Moscow, 117257 Russia *e-mail: skobelev@orc.ru Received July 30, 2001 Abstract—By means of spatially resolved high-resolution X-ray spectroscopy, we have investigated the gen- eration of fast ions at various laser installations with different flux densities and laser wavelengths. It is demon- strated that the fast ion generation in laser-produced plasma can be achieved for a very low level of the averaged laser intensity on the target. The time-of-flight mass spectrometry ion diagnostics and X-ray spectrographs give very close results for the energy distribution of the thermal ion component. For higher energies, however, we found significant differences: the spatially resolved high-resolution spectrographs expose the presence of suprathermal ions, while the time-of-flight method does not. Suprathermal ion energies E ion plotted as a func- tion of the qλ 2 parameter show a large scatter far above the experimental errors. The cause of these large scatters is attributed to a strong nonuniformity of the laser intensity distribution in the focal spot. The analysis by means of hydrodynamics and spectral simulations show that the X-ray emission spectrum is a complex convolution from different parts of the plasma with strongly different electron density and temperature. It is shown that the highly resolved Li-like satellite spectrum near He α contains significant distortions even for very low hot elec- tron fractions. Non-Maxwellian spectroscopy allows determination of both the hot electron fraction and the bulk electron temperature. © 2002 MAIK “Nauka/Interperiodica”. PLASMA, GASES ¶ This article was submitted by the authors in English.