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We report on the results of a joint experimental and numerical study on the sub-cycle laser field-driven electron dynamics that underlie the population of highly excited electronic states in multiply ionized argon dimers by electron recapture processes. Our experiments using few-cycle laser pulses with a known carrier-envelope phase (CEP) in combination with reaction microscopy reveal a distinct CEP-dependence of the electron emission and recapture process and, furthermore, a small but significant CEP-offset to the scenario in which no excited argon dimers are produced. With the help of classical ensemble trajectory simulations we trace down these different CEP-dependencies to subtle differences in the laser-driven sub-cycle electron trajectory dynamics that involve in both cases the transfer of an electron from one argon ion across the system boundary to the neighboring ion and its transient capture on this ion.

We report experiments on the direct observation of O2 formation from CO2 in strong laser fields. Our simulations and pump-probe measurements suggest that CO2 undergos bending motion during strong-field ionization which supports the O2 formation.

We experimentally observed high-lying (n>238) Rydberg states which are formed through recapture of electrons after strong field interaction in atoms and small molecules using electron and ion coincidence detection. The high-lying Rydberg states are identified through weak DC field-induced ionization.

We report experimental observation of "slow" fragmentation from ethylene molecules on nanosecond or even microsecond timescale after their interaction with femtosecond laser pulses. Our results indicate that such fragmentation process originates from meta-stable high-lying vibrational states of ethylene ions.

We have studied the double ionization of Helium induced by intense (up to 1×1016 W/cm2) ultra-short (4-4.5 fs) circularly polarized laser pulses with a stabilized CEO phase.

Single- and double-ionization of neon with orthogonally polarized two-color (OTC) laser fields is investigated using the COLTRIMS method. We study the influence of the long range Coulomb potential of the parent ion on the final momentum distribution of electrons emitted during single ionization. Furthermore, we investigate nonsequential double ionization in OTC fields and demonstrate that the electron-electron correlation is highly sensitive to the sub-cycle field shape of the OTC pulses, in agreement with recent theoretical predictions., 28th International Conference on Photonic, Electronic and Atomic Collisions, ICPEAC 2013, July 24-30, 2013, Lanzhou

Control over various fragmentation reactions of a series of polyatomic molecules (acetylene, ethylene, 1,3-butadiene) by the optical waveform of intense few-cycle laser pulses is demonstrated experimentally. We show both experimentally and theoretically that the responsible mechanism is inelastic ionization from inner-valence molecular orbitals by recolliding electron wave packets.

We show experimentally and theoretically, using acetylene as an example, that the strong preponderance of ionization from specific molecular orbitals to the alignment of the molecular axis with respect to the laser polarization direction allows implementing a method for controlling fragmentation reactions of polyatomic molecules.

We experimentally investigate and control the influence of the Coulomb binding potential on momentum spectra of electron wave packets created by strong-field ionization in a two-color laser field.

We have studied the double ionization of Helium with ultra short intense circularly polarized light pulses at intensities up to 1.5×1016 W/cm2 and pulse durations as short as 5.5 fs.

We report on the observation of an ionization-fragmentation process that puts a polyatomic molecule into a very high charge state of +12 and beyond at laser intensities as low as a few 1014 W/cm2 and subsequently leads to complete molecular decomposition. Our surprising experimental evidence shows that all of the molecule's protons are ejected with high kinetic energies, which is inconsistent with the explanation based on dynamic charge localization used in [1] to explain the proton energy. Furthermore, the energies of all the protons are very similar, which indicates that at the instance of decomposition the protons interact with the same molecular charge state, suggesting an all-at-once (concerted) fragmentation scenario.

We experimentally demonstrate control over interference structures of electron wave packets created and driven by a strong two-color laser field. Interferences of wave packets that are created within the same laser cycle and those that originate from different cycles are identified and controlled by the laser field's shape.

We experimentally studied proton ejection in the three-body fragmentation of triply charged 1,3-butadiene molecules prepared by intense ultrashort laser pulses using coincidence momentum imaging. The break-up dynamics along the four possible paths that a final set of three fragments can be reached is investigated for the three different fragmentation channels that are analysed. It is found that for each channel the two dominant paths are (i) proton ejection from the triply charged ion and (ii) a sequential path, where the proton is ejected from the doubly charged ion during the second fragmentation step. Based on the measured three-body momentum correlations and accompanying numerical simulations, we discuss whether the fragmentation dynamics, where the proton is ejected from the triply charged ion, proceeds concertedly or sequentially. We also investigate the dependence of the fragmentation dynamics on the intensity and polarization state of the laser pulse.

We describe a general concept of using the spatial information encoded in the time-dependent polarization of high harmonic radiation generated by orthogonally polarized two-color laser fields. The main properties of recolliding electron wave packets driven by such fields are reviewed. It is shown that in addition to the recollision energy the angle of recollision of such wave packets, which is directly mapped onto the polarization direction of the emitted high harmonic radiation, varies on a sub-laser-cycle time-scale. Thus, a mapping between the polarization angle and the frequency of the emitted radiation is established on an attosecond time scale. While the polarization angle encodes the spatial properties of the recollision process, the frequency is linked to time via the well-known dispersion relations of high harmonic generation. Based on these principles, we show that in combination with polarization selective detection the use of orthogonally polarized drive pulses for high harmonic generation permit one to construct spatially resolved attosecond measurements. Here, we present two examples of possible applications: (i) a method for isolating a single attosecond pulse from an attosecond pulse train which is more efficient than the cut-off selection method, and (ii) a technique for orbital tomography of molecules with attosecond resolution.