2018, Mero, Mark, Heiner, Zsuzsanna, Petrov, Valentin, Rottke, Horst, Branchi, Federico, Thomas, Gabrielle M., Vrakking, Marc J. J.

We present a 100 kHz optical parametric chirped pulse amplifier (OPCPA) developed for strong-field attosecond physics and soft-x-ray transient absorption experiments. The system relies on noncollinear potassium titanyl arsenate booster OPCPAs and is pumped by a 244 W, 1.1 ps Yb:YAG Innoslab chirped pulse laser amplifier. Two optically synchronized infrared output beams are simultaneously available: a 430 μJ, 51 fs, carrier-envelope phase stable beam at 1.55 μm and an angular-dispersion-compensated, 125 μJ, 73 fs beam at 3.1 μm.

2015, Schütte, Bernd, Arbeiter, Mathias, Fennel, Thomas, Jabbari, Ghazal, Kuleff, Alexander I., Vrakking, Marc J. J., Rouzée, Arnaud

We report on a novel correlated electronic decay process following extensive Rydberg atom formation in clusters ionized by intense near-infrared fields. A peak close to the atomic ionization potential is found in the electron kinetic energy spectrum. This new contribution is attributed to an energy transfer between two electrons, where one electron decays from a Rydberg state to the ground state and transfers its excess energy to a weakly bound cluster electron in the environment that can escape from the cluster. The process is a result of nanoplasma formation and is therefore expected to be important, whenever intense laser pulses interact with nanometer-sized particles.

2015, Schütte, Bernd, Oelze, Tim, Krikunova, Maria, Arbeiter, Mathias, Fennel, Thomas, Vrakking, Marc J. J., Rouzée, Arnaud

We investigate electron-ion recombination processes in clusters exposed to intense extreme-ultraviolet (XUV) or near-infrared (NIR) pulses. Using the technique of reionization of excited atoms from recombination (REAR), recently introduced in Schütte et al (2014 Phys. Rev. Lett. 112 253401), a large population of excited atoms, which are formed in the nanoplasma during cluster expansion, is identified under both ionization conditions. For intense XUV ionization of clusters, we find that the significance of recombination increases for increasing cluster sizes. In addition, larger fragments are strongly affected by recombination as well, as shown for the case of dimers. We demonstrate that for mixed Ar–Xe clusters exposed to intense NIR pulses, excited atoms and ions are preferentially formed in the Xe core. As a result of electron-ion recombination, higher charge states of Xe are efficiently suppressed, leading to an overall reduced expansion speed of the cluster core in comparison to the shell.

2015, Schütte, Bernd, Arbeiter, Mathias, Fennel, Thomas, Jabbari, Ghazal, Gokhberg, Kirill, Kuleff, Alexander I., Vrakking, Marc J. J., Rouzée, Arnaud

We report on the observation of a novel intracluster Coulombic decay process following Rydberg atom formation in clusters ionized by intense near-infrared fields. A new decay channel emerges, in which a Rydberg atom relaxes to the ground state by transferring its excess energy to a weakly bound electron in the environment that is emitted from the cluster. We find evidence for this process in the electron spectra, where a peak close to the corresponding atomic ionization potential is observed. For Ar clusters, a decay time of 87 ps is measured, which is significantly longer than in previous time-resolved studies of interatomic Coulombic decay.

2015, Schütte, Bernd, Vrakking, Marc J. J., Rouzée, Arnaud

We report on the observation of a transient C4+ ion charge state in nanoplasmas produced by the interaction of intense near-infrared (NIR) laser pulses with CH4 clusters. The underlying dynamics are studied by pump-probe spectroscopy, which reveals that the ion charge states are lowered by electron-ion recombination. Furthermore, we present direct evidence that autoionization of multiply-excited ions plays an important role in expanding nanoplasmas, in contrast to models that neglect quantum phenomena.

2018, Schell, Felix, Bredtmann, Timm, Schulz, Claus Peter, Patchkovskii, Serguei, Vrakking, Marc J. J., Mikosch, Jochen

Electrons released by strong-field ionization from atoms and molecules or in solids can be accelerated in the oscillating laser field and driven back to their ion core. The ensuing interaction, phase-locked to the optical cycle, initiates the central processes underlying attosecond science. A common assumption assigns a single, welldefined return direction to the recolliding electron. We study laser-induced electron rescattering associated with two different ionization continua in the same, spatially aligned, polyatomic molecule. We show by experiment and theory that the electron return probability is molecular frame-dependent and carries structural information on the ionized orbital. The returning wave packet structure has to be accounted for in analyzing strong-field spectroscopy experiments that critically depend on the interaction of the laser-driven continuum electron, such as laser-induced electron diffraction.

2019, Karamatskos, Evangelos T., Raabe, Sebastian, Mullins, Terry, Trabattoni, Andrea, Stammer, Philipp, Goldsztejn, Gildas, Johansen, Rasmus R., Długołecki, Karol, Stapelfeldt, Henrik, Vrakking, Marc J. J., Trippel, Sebastian, Rouzée, Arnaud, Küpper, Jochen

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.

2015, Schulz, Claus Peter, Birkner, Sascha, Furch, Federico J., Anderson, Alexandria, Mikosch, Jochen, Schell, Felix, Vrakking, Marc J. J.

Strong field ionization of small hydrocarbon chains is studied in a kinematic complete experiment using a reaction microscope. By coincidence detection of ions and electrons different ionization continua populated during the ionization process are identified. In addition, photoelectron momentum distributions from laser-aligned molecules allow to characterize the electron wavepackets emerging from different Dyson orbitals.