Abstract

High harmonics produced by femtosecond lasers are a convenient source of ultrashort soft x-ray pulses and have been intensively studied in recent years [1]. We use high-order harmonics to measure time-resolved the electron density and the mean electron energy in femtosecond laser produced plasmas [2,3]. Differential absorption of the harmonics as a probe radiation allows to infer plasma free electron densities well above the critical density for the fundamental wavelength. It is shown that this pump-probe technique allows direct access to plasma parameters in conjunction with a time resolution of a few hundred femtoseconds.

© 1997 Optical Society of America