Extreme ultraviolet pulses produced by high order harmonic generation are used to probe ultrafast atomic and molecular dynamics. States of high field ionization, coherent superpositions, and alignment are obtained by core level transient absorption spectroscopy. © OSA 2013.

Extreme ultraviolet pulses produced by high order harmonic generation are used to probe ultrafast atomic and molecular dynamics. States of high field ionization, coherent superpositions, and alignment are obtained by core level transient absorption spectroscopy. © OSA 2013.

Extreme ultraviolet pulses produced by high order harmonic generation are used to probe ultrafast atomic and molecular dynamics. States of high field ionization, coherent superpositions, and alignment are obtained by core level transient absorption spectroscopy. © OSA 2013.

The broad bandwidth of an isolated attosecond pulse excites a vast number of states simultaneously, and the corresponding absorption features can be monitored with exceptional temporal resolution. Novel transient absorption experiments in gases using isolated attosecond pulses are performed in two regimes, one in which the attosecond pulse is overlapped in time with a near-infrared (NIR) pulse and one in which the NIR pulse follows the attosecond pulse. In the latter regime, the attosecond pulse first interacts with a sample, then the observed absorption features are modified by a NIR pulse, which interacts with the sample well after the attosecond pulse has passed. In these experiments, which seem counterintuitive when compared to conventional transient absorption spectroscopy, the weak attosecond pulse induces a polarization of the medium, which is then perturbed by the time-delayed NIR pulse. Recent measurements demonstrate the rich variety of information that can be extracted in this regime.

Electronic coherences are observed in silicon by attosecond transient absorption spectroscopy. Various sub-4 fs oscillations across the conduction band reveal complex couplings between valence-conduction and conduction-conduction bands indicating pathways for coherent preparation of highly excited electrons.

Extreme ultraviolet (XUV) transient absorption at the germanium M4,5-edge simultaneously measures electron and hole dynamics over 1.5 ps with few-femtosecond resolution. In the analysis, time-dependent density functional theory (TD-DFT) will be compared with experimental data.

Attosecond transient absorption spectroscopy of highly excited states allows investigating the dynamics of both the decay and the light induced coupling between excited states. We present a rigorous quantum mechanical treatment that provides a generalized discussion of the on- and off-resonant decay dynamics, of resonant and non-resonant couplings to either discrete or continua states and the temporal evolution of the quantum beating of the excited wavepackets. The comparison of the model to experimental results obtained in xenon proves its general applicability.

Highly crystalline and stable molecular superlattices are grown with the smallest possible stacking period using monolayers (MLs) of the organic semiconductors pentacene (PEN) and perfluoro-pentacene (PFP). Superlattice reflections in X-ray reflectivity and their energy dependence in resonant soft X-ray reflectivity measurements show that PFP and PEN MLs indeed alternate even though the coherent ordering is lost after ∼ 4 ML. The observed lattice spacing of 15.9 Å in the superlattice is larger than in pure PEN and PFP films, presumably because of more upright standing molecules and lack of interdigitation between the incommensurate crystalline PEN and PFP layers. The findings are important for the development of novel organic quantum optoelectronic devices.

A harmonic continuum extending up to 375 eV is generated from 750 μJ, 9 fs mid-IR pulses centered at 1300 nm. The development of this source and its use for attosecond transient absorption spectroscopy experiments at the carbon K-edge are discussed.

The ability to transfer electrons from valence to conduction band states in a semiconductor is the basis of modern electronics. Here, attosecond spectroscopy is used to resolve this process in real-time. The excitation of electrons across the band-gap of silicon by few-cycle laser pulses is found to induce lasting modifications of the XUV absorbance spectrum in steps synchronized with the laser electric field oscillations, indicative of light-field induced electron tunneling [1]. In contrast, in SiO2, a dielectric with 9 eV band-gap, similar excitation pulses are found to cause a transient field-induced polarizability without lasting population transfer [2]. © OSA 2015.