Abstract

The generation of ultrabright and ultrafast x-ray pulses is a challenge in the study of unexplored physics of high density and high temperature plasmas.¹ Such plasmas are produced when an intense ultrashort laser pulse (100 fs, 10^16–17 W/cm²) is focused on solid targets.^2,3 Laser energy absorbed within the laser skin depth gives rise to a thermal plasma of several hundred electron-volts temperature, approaching solid density.⁴ Behind the thermal plasma, fast electrons resulting from the specific interaction of the incident laser light through a very steep density gradient—with a scalelength being only a fraction of the incident laser wavelength—eject inner shell electrons of the target plasma. This produces fluorescence line radiation as the inner shell vacancy is filled from outer shells. Being produced by highly nonlinear effects, the fast electrons are thought to last no longer than the duration of the laser pulse. Up to now, the time duration of the whole x-ray pulse has been found to be less than ~2 ps, the ultimate resolution of ultrafast streak cameras.

© 1994 IEEE