Enhancement of soft x-ray emission from a cryogenically cooled Ar gas jet irradiated by 25 fs laser pulse

Abstract

Soft x-ray spectra (40-180 Angstrom) produced by the interaction of 25 fs laser pulses at an intensity of similar to 7 x 10(16) W/cm(2) with a cryogenically cooled Ar gas jet have been measured. New spectral lines from Ar8+ and Ar9+ charge states appeared with decreasing gas temperature. Nonlinear increase of x-ray line emission from Ar7+, Ar8+, and Ar9+ was observed with cooling, which saturated below certain temperature. The drastic change in the spectrum is attributed to efficient collisional heating and collisional ionization of growing (10(2)-10(3) atoms) Ar clusters from the cooled jet. (C) 2000 American Institute of Physics. [S0003-6951(00)02614-0].