118 research outputs found
Showtime for Molecular Movies
Molecular movies of vibrating iodine molecules have been recorded in time-
resolved x-ray and electron diffraction experiments
Tracing transient charges in expanding clusters
We study transient charges formed in methane clusters following ionization by intense near-infrared laser pulses. Cluster ionization by 400-fs (I=1×1014 W/cm2) pulses is highly efficient, resulting in the observation of a dominant C3+ ion contribution. The C4+ ion yield is very small but is strongly enhanced by applying a time-delayed weak near-infrared pulse. We conclude that most of the valence electrons are removed from their atoms during the laser-cluster interaction and that electrons from the nanoplasma recombine with ions and populate Rydberg states when the cluster expands, leading to a decrease of the average charge state of individual ions. Furthermore, we find clear bound-state signatures in the electron kinetic energy spectrum, which we attribute to Auger decay taking place in expanding clusters. Such nonradiative processes lead to an increase of the final average ion charge state that is measured in experiments. Our results suggest that it is crucial to include both recombination and nonradiative decay processes for the understanding of recorded ion charge spectra
Spatio-temporal characterisation of a 100 kHz 24 W sub-3-cycle NOPCPA laser system
In recent years, OPCPA and NOPCPA laser systems have shown the potential to supersede Ti:sapphire plus post-compression based laser systems to drive next generation attosecond light sources via direct amplification of few-cycle pulses to high pulse energies at high repetition rates. In this paper, we present a sub 3-cycle, 100 kHz, 24 W NOPA laser system and characterise its spatio-temporal properties using the SEA-F-SPIDER technique. Our results underline the importance of spatio-temporal diagnostics for these emerging laser systems
Numerical study of spatiotemporal distortions in noncollinear optical parametric chirped-pulse amplifiers
During amplification in a noncollinear optical parametric amplifier the spatial and temporal coordinates of the amplified field are inherently coupled. These couplings or distortions can limit the peak intensity, among other things. In this work, a numerical study of the spatiotemporal distortions in BBO-based noncollinear optical parametric chirped-pulse amplifiers (NOPCPAs) is presented for a wide range of parameters and for different amplification conditions. It is shown that for Gaussian pump beams, gain saturation introduces strong distortions and high conversion efficiency always comes at the price of strong spatiotemporal couplings which drastically reduce the peak intensity even when pulse fronts of the pump and the signal are matched. However, high conversion efficiencies with minimum spatiotemporal distortions can still be achieved with flat-top pump beam profiles
Ionization avalanching in clusters ignited by extreme-ultraviolet driven seed electrons
We study the ionization dynamics of Ar clusters exposed to ultrashort
near-infrared (NIR) laser pulses for intensities well below the threshold at
which tunnel ionization ignites nanoplasma formation. We find that the emission
of highly charged ions up to Ar can be switched on with unit contrast by
generating only a few seed electrons with an ultrashort extreme ultraviolet
(XUV) pulse prior to the NIR field. Molecular dynamics simulations can explain
the experimental observations and predict a generic scenario where efficient
heating via inverse bremsstrahlung and NIR avalanching are followed by resonant
collective nanoplasma heating. The temporally and spatially well-controlled
injection of the XUV seed electrons opens new routes for controlling
avalanching and heating phenomena in nanostructures and solids, with
implications for both fundamental and applied laser-matter science.Comment: 5 pages, 4 figure
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Spatio-temporal characterisation of a 100 kHz 24 W sub-3-cycle NOPCPA laser system
In recent years, OPCPA and NOPCPA laser systems have shown the potential to supersede Ti:sapphire plus post-compression based laser systems to drive next generation attosecond light sources via direct amplification of few-cycle pulses to high pulse energies at high repetition rates. In this paper, we present a sub 3-cycle, 100 kHz, 24 W NOPA laser system and characterise its spatio-temporal properties using the SEA-F-SPIDER technique. Our results underline the importance of spatio-temporal diagnostics for these emerging laser systems
Roadmap of ultrafast x-ray atomic and molecular physics
X-ray free-electron lasers (XFELs) and table-top sources of x-rays based upon high harmonic generation (HHG) have revolutionized the field of ultrafast x-ray atomic and molecular physics, largely due to an explosive growth in capabilities in the past decade. XFELs now provide unprecedented intensity (1020 W cm−2) of x-rays at wavelengths down to ~1 Ångstrom, and HHG provides unprecedented time resolution (~50 attoseconds) and a correspondingly large coherent bandwidth at longer wavelengths. For context, timescales can be referenced to the Bohr orbital period in hydrogen atom of 150 attoseconds and the hydrogen-molecule vibrational period of 8 femtoseconds; wavelength scales can be referenced to the chemically significant carbon K-edge at a photon energy of ~280 eV (44 Ångstroms) and the bond length in methane of ~1 Ångstrom. With these modern x-ray sources one now has the ability to focus on individual atoms, even when embedded in a complex molecule, and view electronic and nuclear motion on their intrinsic scales (attoseconds and Ångstroms). These sources have enabled coherent diffractive imaging, where one can image non-crystalline objects in three dimensions on ultrafast timescales, potentially with atomic resolution. The unprecedented intensity available with XFELs has opened new fields of multiphoton and nonlinear x-ray physics where behavior of matter under extreme conditions can be explored. The unprecedented time resolution and pulse synchronization provided by HHG sources has kindled fundamental investigations of time delays in photoionization, charge migration in molecules, and dynamics near conical intersections that are foundational to AMO physics and chemistry. This roadmap coincides with the year when three new XFEL facilities, operating at Ångstrom wavelengths, opened for users (European XFEL, Swiss-FEL and PAL-FEL in Korea) almost doubling the present worldwide number of XFELs, and documents the remarkable progress in HHG capabilities since its discovery roughly 30 years ago, showcasing experiments in AMO physics and other applications. Here we capture the perspectives of 17 leading groups and organize the contributions into four categories: ultrafast molecular dynamics, multidimensional x-ray spectroscopies; high-intensity x-ray phenomena; attosecond x-ray science
Interference stabilization of autoionizing states in molecular studied by time- and angular-resolved photoelectron spectroscopy
An autoionizing resonance in molecular N is excited by an ultrashort XUV
pulse and probed by a subsequent weak IR pulse, which ionizes the contributing
Rydberg states. Time- and angular-resolved photoelectron spectra recorded with
a velocity map imaging spectrometer reveal two electronic contributions with
different angular distributions. One of them has an exponential decay rate of
fs, while the other one is shorter than 10 fs. This observation is
interpreted as a manifestation of interference stabilization involving the two
overlapping discrete Rydberg states. A formalism of interference stabilization
for molecular ionization is developed and applied to describe the autoionizing
resonance. The results of calculations reveal, that the effect of the
interference stabilization is facilitated by rotationally-induced couplings of
electronic states with different symmetry.Comment: 8 pages, 6 figure
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