<title>X-ray radiation properties of clusters heated by fs laser pulses</title>

Abstract

Review of systematic investigations of x-ray radiation properties of different clusters heated by short-pulse high- intensive TI:Sa laser radiation is presented. The cluster targets were formed by the adiabatic expansion in vacuum of an Ar or CO<SUB>2</SUB> gas puff produced by a pulsed valve with a Laval or conical nozzles. The gas jet pressure is varied form 15 up to 100 bar. Detailed theoretical modeling of cluster parameters have been done and compared with experimental measurements. High spectrally and spatially resolved x-ray spectra near resonance lines of H- and He- like ions of oxygen and Ar have been obtained and detailed spectroscopic analysis was consistent with a theoretical two-temperature collisional-radiative model of irradiated atomic clusters incorporating with an effects of highly energetic electronics. The role of laser prepulse for x-ray intensity emission and its spatial distribution were investigated in details. X-ray spectra radiation from plasma with electron density more than 10<SUP>22</SUP> cm<SUP>-3</SUP> was at first time observed. Big effect of fast electrons influence on the x-ray emission of He-like Ar spectra was demonstrated. Comparison with data under various experimental conditions clearly demonstrated that for increasing x-ray output form plasma the most essential to increase size of clusters and has reasonable value of ps prepulse.