M. Hentschel

Attosecond control of electronic processes by intense light fields.

The amplitude and frequency of laser light can be routinely measured and controlled on a femtosecond (10-15 s) timescale. However, in pulses comprising just a few wave cycles, the amplitude envelope and carrier frequency are not sufficient to characterize and control laser radiation, because evolution of the light field is also influenced by a shift of the carrier wave with respect to the pulse peak. This so-called carrier-envelope phase has been predicted and observed to affect strong-field phenomena, but random shot-to-shot shifts have prevented the reproducible guiding of atomic processes using the electric field of light. Here we report the generation of intense, few-cycle laser pulses with a stable carrier envelope phase that permit the triggering and steering of microscopic motion with an ultimate precision limited only by quantum mechanical uncertainty. Using these reproducible light waveforms, we create light-induced atomic currents in ionized matter; the motion of the electronic wave packets can be controlled on timescales shorter than 250 attoseconds (250 × 10-18 s). This enables us to control the attosecond temporal structure of coherent soft X-ray emission produced by the atomic currents—these X-ray photons provide a sensitive and intuitive tool for determining the carrier-envelope phase.

Time-resolved atomic inner-shell spectroscopy

The characteristic time constants of the relaxation dynamics of core-excited atoms have hitherto been inferred from the linewidths of electronic transitions measured by continuous-wave extreme ultraviolet or X-ray spectroscopy. Here we demonstrate that a laser-based sampling system, consisting of a few-femtosecond visible light pulse and a synchronized sub-femtosecond soft X-ray pulse, allows us to trace these dynamics directly in the time domain with attosecond resolution. We have measured a lifetime of 7.9-0.9+1.0 fs of M-shell vacancies of krypton in such a pump–probe experiment.

erratum: Attosecond control of electronic processes by intense light fields

This corrects the article DOI: nature01414

XUV-attosecond pulses: generation and measurement

Tunnel emission by and subsequent acceleration of electrons from rare gas atoms in high laser fields has emerged as a powerful process to generate extremely short bursts of electromagnetic radiation in the XUV spectral range. With proper choice of parameters (most importantly, laser driver pulses of only few cycles duration), single XUV-pulses of several 100 attosecond duration can be produced.

Subfemtosecond pulse generation and measurement

Summary from only given. We report the observation of light-field induced modulation of the width of the kinetic energy distribution of photoelectrons from an atomic gas (krypton) excited by an ultrashort 90eV soft-X-ray pulse in the presence of a 7-fs few cycle light pulse carried at a wavelength of 750 nm.

Time-Resolved Inner Shell Spectroscopy with Sub-fs EUV Pulses

Ultrashort high harmonics are applied for a time-domain tracking of decaying atomic inner-shell vacancies. The novel EUV-pump / laser-probe scheme utilizes the delay-dependent momentum exchange between photoemitted electrons and an intense laser field. The relaxation of 3d core holes in krypton was studied in a benchmark experiment demonstrating the capabilities of the technique.

Stabilization and Characterization of the Carrier-Envelope Phase in Intense Few-Cycle Pulses

We demonstrate a phase-stabilized 5-fs 0.1-TW amplified laser system that delivers pulses with exactly reproducible electric fields. Full temporal characterization of the resultant intense few-cycle light waveforms was achieved by combining conventional pulse characterization techniques with observing the signature of soft-X-ray emission.

Phase-controlled amplification of few-cycle laser pulses

Several methods of carrier-envelope-phase stabilization of amplified ultrashort laser pulses are presented. Full temporal characterization of the resultant intense few-cycle light waveforms, reproducible with every laser shot, was achieved by combining conventional pulse characterization techniques with observing the signature of soft-X-ray emission.

Subfemtosecond Pulse Generation and Measurement

We report the generation and measurement of isolated soft‐x‐ray pulses (λx = 14 nm) with a duration of τx = 650 ± 150 attoseconds by using few‐cycle intense visible/near‐infrared (λ0 = 750 nm) laser pulses. For the temporal characterization of the x‐ray pulses, a cross‐correlation technique relying on laser field assisted x‐ray photoemission from Krypton atoms was employed. The experimental results bear direct evidence of the x‐ray pulse being synchronized to the field oscillations of the visible light pulse with attosecond precision and of bound‐free electronic transitions from the 4p state of krypton responding to 90‐eV excitation on an attosecond time scale. As a first demonstration of attosecond metrology, the synchronized single sub‐fs x‐ray pulses were used for tracing the electric field oscillations in a visible light wave with a resolution of better than 150 as.

Toward attosecond metrology

Ultrashort-pulse lasers constitute the fastest probes available for tracing transitions between different states of matter. They allow measuring time intervals on a femtosecond time scale and provide access to fundamental physical, chemical and biological processes on a microscopic scale in the time domain. The fastest speed at which events can be followed is limited by the laser pulse duration. Sub-10 femtosecond pulses are available in the visible and near infrared spectral range. They comprise only a few optical cycles, hence the phase of the carrier with respect to the pulse envelope becomes a significant issue. A method for controlling this phase is described in this paper. Several fundamental atomic processes such as inner-shell electronic relaxation or ionization by optical tunneling, however, take place within a fraction of the oscillation period of visible or near-infrared radiation and require very short probes for being investigated. Isolated bursts of radiation of the order of 1 femtosecond or...