CADAM: Capturing Attosecond Dynamics in Atoms and Molecules

In atoms, molecules or biological systems, all structural changes will modify the properties of the entity (form, colour, capacity to react with other entities etc ...). These changes are due to electronic and nuclear dynamics known as charge migrations (rearrangement of electrons and/or protons within the entity). However charge migrations are very fast and can occurs within 1/1000 000 000 000 000 second meaning from few attosecond (1e-18 sec) to few femtosecond (1e-15 sec). As an example in the Rutherford model of the hydrogen atom, known as the "planetary" model, an electron is moving around a proton (first orbital). The duration the electron takes to complete period around the proton is 150 asec. What is particularly exciting is to be able to make "a movie" of this ultra-fast dynamic that no existing device is capable to follow. My interests are actually not only to observe the first instants of these structural changes but also to control them to go deeper in the understanding of how chemical reactions or biological phenomena take place. If such attosecond information is achieved it will be possible to approach very high-speed information transfer and why not studying how information can be artificially encoded (molecular electronics) or present (traces of cancers) in biological sample, a kind of bio computing?This research will give birth to a new type of Physics that will bridge the gap between many sciences. The technical challenges under this research area are leading international efforts in laser development that will have a huge impact on technological applications also in industry (electronic, communication), medicine technologies (Magnetic Resonance Imaging, proton therapy, pharmacology).Therefore I developed a research based on tools to observe and control the intra- atomic and intra-molecular electrons and nuclei motions. To capture this dynamics at the origin of any chemical or biological reactions, one has to capture snapshots of the system evolving, exactly as a camera will do. Unfortunately there is no such detector, but what is possible is to find a process observable, that can be affected by these changes and so that will carry the fingerprint of these changes. The ideal candidate for this is light, because emission of photons is highly sensitive to any changes, it is a fast process and it can be observable by looking at spectra (frequency equivalent to its colour). The process I choose is high-order harmonic generation (HHG) that occurs within 10's attosec to few fsec (appropriate time window). It occurs while an intense and short laser pulse interacts with an atom or a molecule. During this interaction, an electron is ionised (extract from the core), and follow a certain trajectory before coming back to the core where it can be recaptured, exactly as a returning boomerang. The excess kinetic energy the electron has acquired during its travel will be spent by the system (final atom or molecule) emitting a new photon which frequency (colour) will be an odd harmonic of the fundamental photon (the laser photon). These harmonic photons can be measured accurately so if a change in the core occurs during the electron travel, the characteristic of the photons emitted will be modified. I have been working in the study of high order harmonic and in particular in the understanding of electron trajectories during the process. I demonstrated experimentally that the ionised electron can not only follow one trajectory but many, giving rise to my technique of investigation called Quantum-Path Interferences first demonstrated in atoms. I will use this technique under different conditions to extract the information on charge migration in molecules within the attosecond timescale.

Interdisciplinary aspect of the proposed research programme and the impacts on knowledge, people, skills and training, economy and society:This project requires technological and scientific skills from different areas which include ultrafast laser science, non linear optics, molecular jets cooling, strong field physics, strong field computation and modelling, molecular physics and photochemistry.I propose to take advantage of different laser sources for capturing ultra-fast dynamics in atoms and molecules. The technological skills required are: femtosecond laser sources, synthesis of multicolour-fields with carrier-envelope phase (CEP) stabilisation and high repetition rate systems (fibre laser). This project will benefit to my colleagues from UT Vienna and from USAL Madrid who will provide experimental and theoretical inputs on all these different aspects of HHG. The development of a high repetition rate fibre laser will impact also on research in extreme light-matter interactions and will benefit to my colleagues from Imperial College for whom the fibre laser could be a more appropriate pump for their current OPCPA laser than the commercially available solution. Such mergence of systems will address a lot of compatibility and technological questions (possible patents) and will impact in communities such as plasma physics or particle acceleration. Moreover this type of laser will have huge implications on industry especially in micromachining (drilling of a broader range of materials, prototyping phases to evaluate designs quickly and cost-effectively, and developing technologies such as biotechnology chips devices, electrode layers, and channel layers) and on Society through its potential applications in medicine (laser eyes surgery, DNA nano-dissection, dental ablation etc...). The experimental study of charge migration within molecules will require skills in molecular and atomic physics. The knowhow of molecular alignment in supersonic gas jets is a prerequisite to achieve high degrees of alignment in molecular samples and therefore to obtain the necessary signal levels. The quantum path interference (QPI) method opens a new route for the study of ultra-fast charge migration providing for the first time a self-referenced technique. It is therefore of particular interest for molecular physicists such as my colleagues from CEA-Saclay who can compare for the first time the phase measured by RABBITT to the phase extracted from QPI. One of the aims of applying the QPI technique to molecules is to provide an extension of the study to 'bigger' molecules. This study will directly be conducted for and with my colleagues from chemistry and bio-chemistry from UPMC (internationally recognised as experts in orbital reconstruction formalism and Gabor phase extraction methods) who will provide for this project advanced codes for simulations of more complex molecular configurations. These studies will also benefit my colleagues from Imperial College (physicists) by obtaining results of calculations which can be compared to their experimental data. These skills from many different disciplines will come together in this project for the benefit of a broad range of communities. As well as mixing different levels of researchers, from well established theoreticians and experimentalists to post-docs and students, and industry, the multi-disciplinary nature of this project will provide excellent training grounds for all involved, broadening the scope of research of everyone participating. It is thus highly interdisciplinary skills that will benefits to a broad range of communities included well establish researchers, young scientists for whom gathering expertise will provide more results and visibility, industries and of course it will be of high importance in the training of students as future experts in these related fields.