Abstract

A direct comparative measurement of the dependence on the wavelength of irradiation of the kilovolt x-ray yields [Xe(M) ~ 9 -15 Å and Xe(L) ~ 2.5 - 3.2 Å] multiphoton-induced from Xe clusters by excitation with intense (I > 10¹⁸ W/cm²) femtosecond pulses at 248 nm and 800 nm has been made. The spectroscopic findings demonstrate that the x-ray production is strongly reduced with excitation at the longer wavelength (800 nm). The peak strengths of the Xe(M) and Xe(L) emissions are diminished approximately by factors of 50 - 10² and ~ 3 × 10³, respectively, and significant spectral modifications are also observed. This sharp reduction in the amplitude of excitation rules out a thermal model for the production of kilovolt x-rays [Xe(M) and Xe(L)] from multiphoton excited Xe clusters. These results are consistent with a dynamical mechanism of enhanced coupling which could involve ordered many-electron motions in which a dephasing of the electrons can appreciably influence both the amplitude of excitation and the threshold intensity for inner-shell vacancy production.

© 1997 Optical Society of America