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UDynI Report Summary

Project ID: 307964
Funded under: FP7-IDEAS-ERC
Country: Italy

Final Report Summary - UDYNI (Ultrafast Dynamic Imaging of Complex Molecules)

High-order harmonics are generated when molecules interact with intense and very short laser pulses. Since light is a periodically oscillating electromagnetic field, the outermost electron of the molecule is ionized by the intense laser field, then accelerated in the continuum and brought back to the molecular ion where it may recombine, emitting extreme ultraviolet (XUV) radiation. The spectrum of this radiation shows periodic peaks called high-order harmonics and can be thought of as a "radiography" of the molecule taken from the direction of electron collision and carrying information on its external electronic structure, also known as Highest Occupied Molecular Orbital (HOMO).
However molecules are tridimensional objects, calling for a "tridimensional picture" (i.e. a tomography) of the HOMO.
A HOMO tomography can be obtained by taking several "pictures" of the molecule from different directions and combining all the results. In practice, with suitable all-optical techniques it is possible to align molecules in the laboratory frame and then, by acquiring harmonic spectra at different angles of electron collision, interpret the information retrieved as the HOMO tomography. It is worth noting that the HOMO is the key structure determining how molecules interact with the surrounding environment.

The Udyni project has the ambitious goal to exploit this effect for imaging in real-time the evolution of molecular orbitals after molecular excitation, thus shooting the so-called “molecular movie”.
We established a new laboratory for performing molecular imaging, by implementing innovative state-of-the-art instrumentations and methodologies. We built a high-energy pulsed mid-infrared laser source capable of generating high-order harmonics in the molecular targets at a high repetition rate. Such pulses are ideal for extending the tomography of molecular orbitals to fragile and complex molecules. We demonstrated the application of molecular orbital tomography to simple hydrocarbons, like acetylene and ethylene, showing the applicability of this technique to organic compounds. The intrinsic complexity of this method has hindered so far its wide exploitation. During the Udyni project, we developed novel experimental and theoretical approaches in collaboration with several international groups and we are now very close to the realization of a "molecular movie" with unprecedented temporal and spatial resolutions.

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