CADAM: Capturing Attosecond Dynamics in Atoms and Molecules

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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.