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An autoionizing resonance in molecular N2 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 20 ± 5 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 suggest, that the effect of the interference stabilization is facilitated by rotationally-induced couplings of electronic states with different symmetry. [ABSTRACT FROM AUTHOR]

Recent advances in the generation and characterization of extreme-ultraviolet pulses, generated either by intense femtosecond lasers or by free electron lasers, are pushing the frontier of time-resolved investigations down to the attosecond domain, the relevant timescale for electron motion. The quantum nature of the intertwined electronic and nuclear motion requires theoretical models going beyond the Born–Oppenheimer approximation and taking into account electron correlation, representing a challenge for the computational power available nowadays. Understanding how the electron dynamics inside molecules can influence chemical reactions presents important implications in several fields and allows for the development of new technologies. In this paper, we report on experimental and theoretical results of an investigation in H_2/D_2, where for the first time control of molecular dynamics with attosecond resolution was achieved. The data represent the first evidence of the control of the electron motion in a molecule undergoing a chemical reaction on the subfemtosecond scale. [ABSTRACT FROM PUBLISHER]

We describe the recent emergence of attosecond science, assessing the present state of the art and discussing several recent examples where attosecond electron dynamics has been studied in atomic and molecular systems. After introducing the generation and characterization of attosecond laser pulses, we describe the use of isolated attosecond pulses in a pump-probe experiment revealing the subcycle time dependence of a multiphoton ionization process and an experiment using the interference from a train ofattosecond pulses to extract amplitude and phase information for electronic wave functions. We furthermore discuss experiments where ultrashort laser pulses with a reproducible waveform control electron dynamics in the D2+ molecular ion on attosecond timescales. Attosecond sci- ence is coming of age and presently is reaching a level of maturity and sophistication that allows detailed investigations of the role of multielectron dynamics in physics and chemistry. [ABSTRACT FROM AUTHOR]

The article presents information according to which X-ray techniques can be used to capture the dynamics of electron density in a hydrogen atom and a crystalline powder of potassium dihydrogen phosphate. It mentions that electronic wave functions can be studied by diffraction of an X-ray free electron laser (FEL). It also states that experiments based on X-ray FEL, laser plasmas and high-harmonic generation helps in analyzing the inner dynamics of materials.

Recording molecular movies on ultrafast timescales has been a longstanding goal for unravelling detailed information about molecular dynamics. Here we present the direct experimental recording of very-high-resolution and -fidelity molecular movies over more than one-and-a-half periods of the laser-induced rotational dynamics of carbonylsulfide (OCS) molecules. Utilising the combination of single quantum-state selection and an optimised two-pulse sequence to create a tailored rotational wavepacket, an unprecedented degree of field-free alignment, 〈cos2θ2D〉 = 0.96 (〈cos2θ〉 = 0.94) is achieved, exceeding the theoretical limit for single-pulse alignment. The very rich experimentally observed quantum dynamics is fully recovered by the angular probability distribution obtained from solutions of the time-dependent Schrödinger equation with parameters refined against the experiment. The populations and phases of rotational states in the retrieved time-dependent three-dimensional wavepacket rationalises the observed very high degree of alignment. Molecular movies provide crucial information of fundamental processes like energy and charge transfer, bond breaking etc. Here the authors show the time evolution of the rotational wave packet called the molecular movie of OCS molecules by Coulomb explosion imaging. [ABSTRACT FROM AUTHOR]

The development of schemes for coherent nonlinear time-domain spectroscopy in the extreme-ultraviolet regime (XUV) has so far been impeded by experimental difficulties that arise at these short wavelengths. In this work we present a novel experimental approach, which facilitates the timing control and phase cycling of XUV pulse sequences produced by harmonic generation in rare gases. The method is demonstrated for the generation and high spectral resolution characterization of narrow-bandwidth harmonics (≈14 eV) in argon and krypton. Our technique simultaneously provides high phase stability and a pathway-selective detection scheme for nonlinear signals—both necessary prerequisites for all types of coherent nonlinear spectroscopy. [ABSTRACT FROM AUTHOR]

An extreme-ultraviolet (XUV) laser pulse consisting of harmonics of a fundamental near-infrared (NIR) laser frequency is combined with the NIR pulse to systematically study two-color photoionization of helium atoms. A time-resolved photoelectron spectroscopy experiment is carried out where energy- and angle-resolved photoelectron distributions are obtained as a function of the NIR intensity and wavelength. Time-dependent Schrödinger equation calculations are performed for the conditions corresponding to the experiment and used to extract residual populations of Rydberg states resulting from excitation by the XUV + NIR pulse pair. The residual populations are studied as a function of the NIR intensity (3.5 × 1010 − 8 × 1012 W cm−2) and wavelength (760–820 nm). The evolution of the photoelectron distribution and the residual populations are interpreted using an effective restricted basis model, which includes the minimum set of states relevant to the features observed in the experiments. As a result, a comprehensive and intuitive picture of the laser-induced dynamics in helium atoms exposed to a two-color XUV–NIR light field is obtained. [ABSTRACT FROM AUTHOR]

We report on a combined experimental and theoretical study of XUV ionization of atomic argon in the presence of a near-infrared (NIR) laser field. Using a table-top source of wavelength-selected femtosecond XUV pulses in combination with a velocity map imaging spectrometer we record angle- and energy-resolved photoelectron distributions and simulate the experimental data by solving the time-dependent Schrödinger equation ab initio. In order to compare with the experimental data we average the calculated energy-angle probability distributions over the experimental focal volume for different values of the magnetic quantum number of the photoelectron. This averaging procedure washes out the intracycle interference pattern, which would otherwise be observed in the form of angular modulations of the photoelectron spectra. We recover these modulations experimentally and in the simulations by evaluating the difference between two averaged distributions that are obtained for slightly different NIR laser field intensities. [ABSTRACT FROM AUTHOR]

The article cites a research study that examines laser-induced electron rescattering associated with two different strong-field ionization (SFI) continuum channels. The two channels are separated by means of a coincidence measurement. The electron return probability was found to be molecular frame-dependent and carry structural information on the ionized orbital.

Subcycle strong-field ionization (SFI) underlies many emerging spectroscopic probes of atomic or molecular attosecond electronic dynamics. Extending methods such as attosecond high harmonic generation spectroscopy to complex polyatomic molecules requires an understanding of multielectronic excitations, already hinted at by theoretical modeling of experiments on atoms, diatomics, and triatomics. Here, we present a direct method which, independent of theory, experimentally probes the participation of multiple electronic continua in the SFI dynamics of polyatomic molecules. We use saturated (n-butane) and unsaturated (1,3-butadiene) linear hydrocarbons to show how subcycle SFI of polyatomics can be directly resolved into its distinct electronic-continuum channels by above-threshold ionization photoelectron spectroscopy. Our approach makes use of photoelectron-photofragment coincidences, suiting broad classes of polyatomic molecules. [ABSTRACT FROM AUTHOR]

Entanglement is one of the most intriguing aspects of quantum mechanics and lies at the heart of the ongoing second quantum revolution, where it is a resource that is used in quantum key distribution, quantum computing, and quantum teleportation. We report experiments demonstrating the crucial role that entanglement plays in pump-probe experiments involving ionization, which are a hallmark of the novel research field of attosecond science. We demonstrate that the degree of entanglement in a bipartite ion + photoelectron system, and, as a consequence, the degree of vibrational coherence in the ion, can be controlled by tailoring the spectral properties of the attosecond extreme ultraviolet laser pulses that are used to create them. [ABSTRACT FROM AUTHOR]

We report experiments on laser-assisted electron recollisions that result from strong-field ionization of photoexcited I2 molecules in the regime of low-energy electron scattering (<25 eV impact energy). By comparing differential scattering cross sections extracted from the angle-resolved photoelectron spectra to differential scattering cross sections from quantum-scattering calculations, we demonstrate that the electron-scattering dynamics is dominated by a shape resonance. When the molecular bond stretches during the evolution of a vibrational wave packet this shape resonance shifts to lower energies, both in experiment and theory. We explain this behavior by the nature of the resonance wave function, which closely resembles an antibonding molecular orbital of I2. [ABSTRACT FROM AUTHOR]

Clusters and nanoparticles have been widely investigated to determine how plasmonic near fields influence the strong-field induced energetic electron emission from finite systems. We focus on the contrary, i.e., the slow electrons, and discuss a hitherto unidentified low-energy structure (LES) in the photoemission spectra of rare gas clusters in intense near-infrared laser pulses. For Ar and Kr clusters we find, besides field-driven fast electrons, a robust and nearly isotropic emission of electrons with <4 eV kinetic energies that dominates the total yield. Molecular dynamics simulations reveal a correlated few-body decay process involving quasifree electrons and multiply excited ions in the nonequilibrium nanoplasma that results in a dominant LES feature. Our results indicate that the LES emission occurs after significant nanoplasma expansion, and that it is a generic phenomenon in intense laser nanoparticle interactions, which is likely to influence the formation of highly charged ions. [ABSTRACT FROM AUTHOR]