title: Attosecond metrology.
abstract: The generation of ultrashort pulses is a key to exploring the dynamic behaviour of matter on ever-shorter timescales. Recent developments have pushed the duration of laser pulses close to its natural limit-the wave cycle, which lasts somewhat longer than one femtosecond (1 fs = 10-15 s) in the visible spectral range. Time-resolved measurements with these pulses are able to trace dynamics of molecular structure, but fail to capture electronic processes occurring on an attosecond (1 as = 10-18 s) timescale. Here we trace electronic dynamics with a time resolution of </= 150 as by using a subfemtosecond soft-X-ray pulse and a few-cycle visible light pulse. Our measurement indicates an attosecond response of the atomic system, a soft-X-ray pulse duration of 650 +/- 150 as and an attosecond synchronism of the soft-X-ray pulse with the light field. The demonstrated experimental tools and techniques open the door to attosecond spectroscopy of bound electrons.
authors.affiliation: Institut für Photonik, Technische Universität Wien, Gusshausstr. 27, A-1040 Wien, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Hentschel
authors.forename: R
authors.initials: R
authors.lastname: Kienberger
authors.forename: C
authors.initials: C
authors.lastname: Spielmann
authors.forename: G A
authors.initials: GA
authors.lastname: Reider
authors.forename: N
authors.initials: N
authors.lastname: Milosevic
authors.forename: T
authors.initials: T
authors.lastname: Brabec
authors.forename: P
authors.initials: P
authors.lastname: Corkum
authors.forename: U
authors.initials: U
authors.lastname: Heinzmann
authors.forename: M
authors.initials: M
authors.lastname: Drescher
authors.forename: F
authors.initials: F
authors.lastname: Krausz