Institut des Sciences Moléculaires d'Orsay




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Accueil > Équipes scientifiques > Dynamiques et Interactions : Rayonnement, Atomes, Molécules (DIRAM) > Processus moléculaires contrôlés par des lasers intenses : Dynamiques électronique et nucléaire > Femtosecond Electron Diffraction

Femtosecond Electron Diffraction

par Saugout Sébastien - 21 juin 2010 (modifié le 26 mai 2015)

In this research topic that follows the Coulomb explosion (see Coulomb explosion of H_2 using intense sub-10fs laser pulses), we study the possibility of a novel electron diffraction technique in gas phase using ultrashort laser pulses and the subsequent attosecond physics. This technique should allow the study of the structure of transient molecular species with a femtosecond temporal resolution and an Angström spatial resolution.

This project is part of the ongoing collaboration with Christian Cornaggia, here with the "Image Femto" ANR Project. The idea behind this electron diffraction technique is the rescattering mechanism. We suggest controlling this mechanism to use the electron as an ultrafast diffraction probe. The very nature of the rescattering mechanism provides a femtosecond temporal resolution and by carefully choosing the laser parameters, it is possible to adjust the wavelength of the electron so it corresponds to the molecular internuclear distance.

On the experimental front, the study of the photoelectron spectra coming from non aligned molecules showed that the molecular specificities can be detected in the angular distributions [1] and in the electron signal coming from the rescattering mechanism [2]. On the theoretical front, early results on CO_2 using a 2D "soft core" potential of an aligned molecule in interactio with a 800-nm and 1-optical-cycle laser pulse make us believe that the geometrical structure of the molecule appears in the photoelectron spectra. Fig. 1 shows the electronic wavefunction of CO_2 with the electric field E of the laser pulse at two different times, t_1 and t_2 > t_1. At t_1, the electronic wavefunction is already away from the molecule and is coming back to the parent ion, due to the direction of the electric field. At t_1, the electron passed the nuclei and has therefore interacted with it. The interference fringes that have appeared may contain information concerning the molecular internuclear distance or the symmetry of the system at the moment of the rescattering.

Figure 1. CO_2 electronic wavefunction as a function of spatial coordinates y and z at 2 different times t_1 and t_2.

[1] C. Cornaggia, Phys. Rev. A 78, 041401® (2008)
[2] C. Cornaggia , J. Phys. B 42, 161002 (2009)