Formation clusters in different gas jet nozzles and their radiation properties under interaction with high-intensive fs laser pulses

Summary form only given, as follows. A review of X-ray radiation properties investigations of different clusters heated by short-pulse high-intensive laser radiation is presented. Cluster targets were formed by adiabatic expansion in vacuum of Ar, CO/sub 2/, Kr gas puff produced by a pulsed valve with Laval or conical nozzles. The gas jet pressure is varied from 15 up to 100 bar. The density of gas after the nozzle was characterized by interferometry. Detailed measurements of cluster parameters have been done by different methods and the obtained data were compared with the theoretical modeling, which included the two-phase. gasdynamic processes in nozzle forming jet and permitted to obtain the spatial distribution of cluster parameters in gas jet, to take in the account shape of nozzles and explain some experimental results. Two sets of experiments, where different types of clusters were irradiated by short pulse (Ti:Sa lasers with energy 600 mJ, duration 60 fs and peak laser intensity 7/spl times/10/sup 17/ W/cm/sup 2/ and correspondingly, energy 15 mJ, duration 35 fs and peak laser intensity about 10/sup 17/ W/cm/sup 2/) have been done. High spectrally (l/dl=2000-5000) and spatially (40-80 microns) resolved X-ray spectra near resonance lines of H- and He-like ions of Oxygen and Ar, and Ne-like lines of Kr have been obtained and detailed spectroscopic analysis was consistent with a theoretical two-temperature collisional-radiative model of irradiated atomic clusters incorporating with the effects of highly energetic electrons. The effect of fast electrons on X-ray emission spectra of femtosecond laser-produced-plasma that was created by the interaction of picosecond laser pre-pulse with clusters were considered. Comparison with data under various experimental conditions clearly demonstrated that for increasing the X-ray output from plasma the most essential point is to increase the size of clusters and at the same time increasing laser energy and flux density is not so important.