High power, high repetition rate laser-based sources for attosecond science

Within the last two decades attosecond science has been established as a novel research field providing insights into the ultrafast electron dynamics that follows a photoexcitation or photoionization process. Enabled by technological advances in ultrafast laser amplifiers, attosecond science has been in turn, a powerful engine driving the development of novel sources of intense ultrafast laser pulses. This article focuses on the development of high repetition rate laser-based sources delivering high energy pulses with a duration of only a few optical cycles, for applications in attosecond science. In particular, a high power, high repetition rate optical parametric chirped pulse amplification system is described, which was developed to drive an attosecond pump-probe beamline targeting photoionization experiments with electron-ion coincidence detection at high acquisition rates

Single-Size Thermometric Measurements on a Size Distribution of Neutral Fullerenes

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A beam experiment on excimer formation in collisions of Kr*(3P0), Kr*(3P2), and Xe* atoms with Br-containing molecules

The reactions of metastable Kr* and Xe* atoms with several Br-containing molecules are studied with a beam-gas experimental apparatus. For Kr*, state selection of the metastable atom beam is employed to investigate the influence of the initial fine-structure state Kr*(3P0) and Kr*(3P2) on the reaction. Trial-and-error simulation of the observed emission spectra results in modified potential energy curves for the X, A(3/2), B, and C states of the KrBr and XeBr excimer products and corresponding transition moments. The propensity for conservation of the Kr+(2P1/2) ion core in the reactions of Kr*(3P0) is observed to be between 36% and 51%, depending on the target, while for the Kr+(2P3/2) core the propensity is close to 100%. This is in general agreement with the results of Sadeghi, Cheaib, and Setser [J. Chem. Phys. 90, 219 (1989)] for Ar*. The reactive cross section is appreciably smaller for Kr*(3P0) than for Kr*(3P2). For several reagents, the analysis leads to a preference for formation of KrBr and XeBr in the C state, different from results of flowing afterglow experiments. This points to incomplete correction for collisional relaxation and for overlap of B→X and C→A(3/2) emission in previous work. For most reagents, the vibrational distributions are analogous for both XeBr and KrBr in both the C and B states. For XeBr(B), the results are generally in agreement with the work of Tamagake, Kolts, and Setser [J. Chem. Phys. 74, 4286 (1981)]

Photoelectron angular distributions from the ionization of xenon Rydberg states by midinfrared radiation

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Single-Size Thermometric Measurements on a Size Distribution of Neutral Fullerenes

We present measurements of the velocity distribution of electrons emitted from mass-selected neutral fullerenes, performed at the intracavity free electron laser FELICE. We make use of mass-specific vibrational resonances in the infrared domain to selectively heat up one out of a distribution of several fullerene species. Efficient energy redistribution leads to decay via thermionic emission. Time-resolved electron kinetic energy distributions measured give information on the decay rate of the selected fullerene. This method is generally applicable to all neutral species that exhibit thermionic emission and provides a unique tool to study the stability of mass-selected neutral clusters and molecules that are only available as part of a size distribution

Angle-resolved photoelectron spectroscopy of sequential three-photon triple ionization of neon at 90.5 eV photon energy

Multiple photoionization of neon atoms by a strong 13.7 nm (90.5 eV) laser pulse has been studied at the FLASH free electron laser in Hamburg. A velocity map imaging spectrometer was used to record angle-resolved photoelectron spectra on a single-shot basis. Analysis of the evolution of the spectra with the FEL pulse energy in combination with extensive theoretical calculations allows the ionization pathways that contribute to be assigned, revealing the occurrence of sequential three-photon triple ionization

Photoelectron angular distributions from the ionization of xenon Rydberg states by midinfrared radiation

Angle-resolved photoelectron spectra, resulting from the strong-field ionization of atoms or molecules, carry a rich amount of information on ionization pathways, electron dynamics, and the target structure. We have investigated angle-resolved photoelectron spectra arising from the nonresonant ionization of xenon Rydberg atoms in the multiphoton regime, using intense midinfrared radiation from a free-electron laser. The experimental data reveal a rich oscillatory structure in the low-order above-threshold ionization region. By performing quantum-mechanical and semiclassical calculations, the observed oscillations could be well reproduced and explained by both a multiphoton absorption picture as by a model invoking electron wave-packet interferences. Furthermore, we demonstrate that the shape and orientation of the initial Rydberg state leaves its own fingerprint on the final angular distribution. DOI: 10.1103/PhysRevA.87.03341

Scaling Laws for Photoelectron Holography in the Midinfrared Wavelength Regime

Midinfrared strong-field laser ionization offers the promise of measuring holograms of atoms and molecules, which contain both spatial and temporal information of the ion and the photoelectron with subfemtosecond temporal and angstrom spatial resolution. We report on the scaling of photoelectron holographic interference patterns with the laser pulse duration, wavelength, and intensity. High-resolution holograms for the ionization of metastable xenon atoms by 7-16 mu m light from the FELICE free electron laser are presented and compared to semiclassical calculations that provide analytical insight