Influence of ultrashort laser pulse duration on the X-ray emission spectrum of plasma produced in cluster target

Line emission spectrum of a laser plasma produced in an argon cluster jet t arget was measured on the n(1)P(1)-1(1)S(0) (n = 5-9) transitions of the he lium-like Ar XVII ion for a pulse duration varying from 45 fs to 1.1 ps and a constant fluence of similar to 10(5) J/cm(2). The independent modeling o f the relative intensities of the transitions from the n = 5, ..., 10 level s, as well as of the 2(1)P(1)-1(2)S(0) and 2(3)P(1)-1(2)S(0) lines and diel ectronic satellites indicates that the electron temperature is anomalously low and that the electron density in emitting plasma increases with shorten ing the laser pulse. The excitation from the ground state by a small fracti on of hot electrons is expected to be the main channel of populating the Ar XVII levels. (C) 2001 MAIK "Nauka/ Interperiodica".