Imaging molecular dynamics with attosecond wavepackets – ATTO-WAVE

Tracking the electronic motion in time and space is a main challenge of forthcoming matter science (DOE report 2007). To resolve electron dynamics in matter at the femtosecond time scale or less, attosecond pulses are needed. Since 2001 and first generation of attosecond light pulses, the field has expanded so rapidly that one speaks now of 'attosecond technology' and 'attosecond science'. At the core of ATTOWAVE, we aim at producing ultra-broadband coherent pulses of both light and electron matter waves, to make them interact with a molecule, and to extract simultaneously temporal and spatial information on the system from the signatures of the coherent interactions. On the one hand, the laser-driven interaction of an electron wavepacket with a molecule leading to high harmonic generation (HHG) and, on the other hand, the photoionization (PI) of the molecule by broadband coherent light pulse, are two facets of the above program: the complete characterization of the outgoing wavepacket gives access to the transition dipole moment that couples the stationary valence orbitals to large continua. The dipole contains information on the electronic structure of the system that can thus be retrieved. This quantum imaging in space and time with Angström and attosecond resolution, respectively, would allow unprecedented insight into matter. To reach this ambitious goal, we need to develop robust techniques compatible with future diverse applications. The first objective of ATTOWAVE is to combine investigations of HHG and of PI using HHG sources, to assess their convergence, as well as differences due to the complex HHG physics. In a first step, the imaging of static orbitals based on HHG will be examined experimentally and theoretically. This implies an improved experimental dipole mapping (amplitude & phase) and a detailed theoretical description of the assumptions underlying the tomographic reconstruction. In particular we will investigated the possible contributions to HHG of multiple orbitals by comparing the HHG dipoles to that extracted from PI of laser-aligned molecules, using vectorial correlations. This analysis would give access to the sub-fs, sub-Å electronic motion in laser-excited molecules. We will also investigate whether the dipole phase could be extracted from coherent XUV+IR multiphoton PI, thus allowing direct orbital imaging based on PI. The second objective of ATTOWAVE is to demonstrate the potential of direct time-resolved studies using ultrashort pulses. First, we will investigate time-resolved imaging, an extremely challenging experiment in terms of experimental tools and techniques. Our exploratory studies will demonstrate that HHG'based imaging can efficiently capture physically significant images of transient electronic orbitals. We will investigate the feasibility in two cases: the acetylene-vinylidene isomerisation and the nitrous oxide dissociation. The second type of experiments will focus on PI with attosecond pulses. Coherent XUV+IR multiphoton PI is a rich process where many interfering pathways allow coherent control of PI on an attosecond timescale, and give access to the various phases involved in the process. Finally, we will investigate the coupling between electron and nuclear dynamics in two benchmark cases: dissociative PI of H2 will be induced either by few-fs XUV pulses through resonant excitation, or by XUV attosecond pulse trains, allowing a coherent control of the nuclear dynamics. The third objective of ATTOWAVE is to develop the essential 'atto laser' tools needed in our ambitious program and to strengthen their quality/control/robustness. We will extend the performances of the driving lasers in terms of ultrashort pulse duration, energy, wavelength tunability and repetition rate. We will develop Optical Parametric Amplifiers based on Difference Frequency Generation producing phase-stabilized ultrashort mid-IR laser pulses. Also, a new compression technique based on cross polarized waves will be implemented. In the XUV, we will develop a new generation of XUV sources delivering single attosecond pulses at the µJ level, a factor 100 above current sources. Finally, we will develop a multi-kHz laser driven HHG source that will greatly facilitate PI studies in VC mode. It will be a unique tool for studying ultrafast molecular dynamics. The project gathers the SPAM-CELIA-ISMO-LCPMR laboratories, with internationally recognized, experimental and theoretical expertises in HHG, PI, femtochemistry, laser R&D. This complementarity enables an exceptional concerted effort towards the ambitious goal of ultra-fast imaging of molecular dynamics. In terms of tools for HHG and PI, the applicants gather knowledge and technology, which are among the best worldwide. In a very competitive international environment, ATTOWAVE federates efforts of French communities in laser physics and molecular dynamics to make the highly promising field of attosecond science to emerge.