Deep ionization and efficient acceleration of primary ions from front surface of laser-purified target

In this paper, we present atomic energy and charge spectra of ions accelerated at the front of the silicon and tungsten targets irradiated by the high-contrast femtosecond laser pulse with the intensity of 3·10¹⁶ W/cm², which is delayed with respect to the cleaning nanosecond laser pulse of the 3-J/cm² energy density. The tremendous increase in the number of fast primary ions (Si or W) and significant growth of their maximum charge in the case of the cleaned target has been observed. The main specific features of the energy and charge spectra have been analyzed by means of one-dimensional hydrodynamic transient-ionization modeling. We are also discussing the possible impact from above threshold ionization by ambipolar field on the generation of deeply ionized fast ions.