Α 10-gigawatt attosecond source for non-linear XUV optics and XUV-pump-XUV-probe studies.

The quantum mechanical motion of electrons and nuclei in systems spatially confined to the molecular dimensions occurs on the sub-femtosecond to the femtosecond timescales respectively. Consequently, the study of ultrafast electronic and, in specific cases, nuclear dynamics requires the availability of light pulses with attosecond (asec) duration and of sufficient intensity to induce two-photon processes, essential for probing the intrinsic system dynamics. The majority of atoms, molecules and solids absorb in the extreme-ultraviolet (XUV) spectral region, in which the synthesis of the required attosecond pulses is feasible.

Ultimate Limit in the Spectral Resolution of Extreme Ultraviolet Frequency Combs.

We present the results of direct interferometric measurements on the pulse-to-pulse phase jitter of a metrological, fiber-based, infrared (IR) frequency comb. We show that the short-time evolution of such phase fluctuations, which cannot be actively controlled by any feedback system, imposes a stringent limit on the tooth linewidth of extreme ultraviolet (XUV) combs produced by high-order harmonic conversion, thus explaining the difference of 9 orders of magnitude between the coherence times of state-of-the-art IR and XUV frequency combs.

An ultrastable Michelson interferometer for high-resolution spectroscopy in the XUV.

We developed an ultra-stable and accurately-controllable Michelson interferometer to be used in a deeply unbalanced arm configuration for split-pulse XUV Ramsey-type spectroscopy with high-order laser harmonics. The implemented active and passive stabilization systems allow one to reach instabilities in the nanometer range over meters of relative optical path differences. Producing precisely delayed pairs of pump pulses will generate XUV harmonic pulses that may significantly improve the achievable spectral resolution and the precision of absolute frequency measurements in the XUV.

Method for high-resolution frequency measurements in the extreme ultraviolet regime: random-sampling Ramsey spectroscopy.

Ramsey-like schemes have been recently introduced in combination with high-order laser harmonic sources for high-resolution spectroscopic studies in the extreme ultraviolet (XUV). Here we demonstrate a novel method, combining measurements only in a limited subset of randomly chosen time-sampling intervals, which lead us to perform the first high-resolution XUV spectroscopy of atomic argon with a simple split-pulse setup. Providing an experimentally simple and convenient solution to the problem of performing high-resolution absolute frequency measurements in the XUV, our approach will help paving new roads into this challenging spectral territory.

Split-pulse spectrometer for absolute XUV frequency measurements.

A split-pulse spectrometer based on pairs of time-delayed femtosecond pulses can give access to accurate frequency measurements in the extreme ultraviolet (XUV) spectral domain. We demonstrate this approach by measuring the absolute frequency of a single-XUV-photon transition to a bound state of atomic argon excited with the ninth harmonic of an amplified Ti:sapphire laser.