ИСТИНА

The experimental results on the interaction of relativistic femtosecond laser pulse with the front surface of dense target are presented. In experiment Ti:Sa laser pulse (wavelength — 800 nm, pulse duration — 45 fs, maximum intensity on target — 4 1018 W/cm2) irradiate teflon, molybdenum, silicon and polyethylene target; the ions were registered with the use time-of-flight spectrometer with charge-to-mass (����/����) separation in the presence of magnetic field. In experiments high charged ions up to C6+, Si12+ and Mo14+ (which not observed in experiments on thin foils) were registered. It was demonstrated that in dense target the electron impact ionization at plasma plume expansion is the main process leading to generation of high charge ions. Also it was demonstrated, that the efficiency of protons and high charge ions acceleration (as well as their charge state composition) is mainly defined by the contrast of the laser radiation. At low contrast level (about 10−8) the high charged ions up to C6+, Si12+ and Mo14+ with a maximum energy from 0.5 to 1 MeV were registered from polyethylene, teflon, silicon and molybdenum, respectively. In the case of a metal target the appreciable drop in acceleration efficiency of protons from the thin organic surface layer was observed, which is the evidence of the cleaning effect of the target surface by the action of the prepulse. The measurements with high contrast (< 10−10) laser radiation have shown the presence of fast protons (up to 300 − 700 keV) on every target and decrease of energies and charge state of high charge ions simultaneously. The authors acknowledge the support from RFBR, grant No. 16-02-00263.