Abstract

We investigated the effect of an intense dressing field on the energies of electrons ejected in an Auger process by means of pump–probe electron spectroscopy. An amplified Ti:s laser provides infrared (800 nm) pulses of 40 mJ ranging from 150 femtoseconds to 8 picoseconds.¹ The infrared pump beam is focused onto a liquid metal (gallium) target to produce broadband XUV radiation. Auger electrons resulting from the XUV-induced LMM transition in argon² are detected in a time-of-flight electron spectrometer. When the XUV pump beam and the infrared probe beam overlap in space and time, sidebands appear around the Auger peaks, corresponding to absorption or emission of photons from the dressing field.³ The lowest order sidebands (i.e., those corresponding to absorption or emission of a single photon) scale linearly with intensity up to a saturation intensity of 10¹³ W/cm². Recording the amplitude of the sidebands as a function of time delay between pump and probe beams provides a measurement of the XUV pulse duration. For radiation in the 250–400 eV range, corresponding to a maximum in the argon photoabsorption cross section, we observed a duration of 0.7 picoseconds. This duration is an order of magnitude less than that observed in the 90 eV range (17 picoseconds).⁴

© 1994 IEEE