Direct spectroscopic observation of multicharged MeV ions inplasma, heated by intense femtosecond laser radiation

摘要

Summary form only given, as follows. Experimental and theoreticalinvestigations of multicharged ions acceleration by an intensefemtosecond laser radiation in wide(10¹⁷-4-10¹⁸W/cm²) laser flux densityrange is presented. With the help of focusing spectrometers with spatialresolution (FSSR-1,2D) we have observed evidence of the emission ofenergetic He- and H-like ions in fluorine of more than 1 MeV producedvia the optical field ionization (OFI) from solid target irradiated byintense I=(1-4)·10¹⁸ W/cm² (UHI-10 laserfacility, 60 fs, λ=800 nm), obliquely incident p-polarized pulselaser. The measured blue wing of He_α, He_β and Ly_α lines of fluorine shows aDoppler-shifted spectrum due to the self-similar ion expansion dominatedby superthermal electrons with the temperature T_h~100-400keV. Using a collisional particle-in-cell simulation, which incorporatesthe nonlocal-thermodynamic-equilibrium ionization including OFI, weobtained the plasma temperature, line shapes, hot electron spectra andmaximal energy of accelerated ions, which agree well with thosedetermined from experimental hot electrons and ions spectra. The redwing of ion spectra gives the temperature of bulk plasma electrons. Byusing simultaneously 3 FSSR spectrometers we also obtained X-ray spectrawith 3D spatial distribution forHe_α-K_α lines of Al, Ca and Cu targets.Such spectra clearly show that the size of emission zone of Ka radiationon the target surface in 2-5 times large, than the size of emission zoneof Ka lines and their satellites. At the same time the size of all linesemission in the direction of laser-plasma expansion were equal.Interpretation of such an effect is presented