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Accueil > Équipes scientifiques > Dynamiques et Interactions : Rayonnement, Atomes, Molécules (DIRAM) > Processus moléculaires contrôlés par des champs laser intenses > Intense laser controlled molecular processes

Intense laser controlled molecular processes

par Atabek Osman - 30 avril 2010 (modifié le 26 mai 2015)

Intense laser fields produce strong internal distorsions in molecules and induce selective dynamical effects that can be exploited in designing control strategies. These strategies rest on some resonances and their underlying basic mechanisms which act either in complementary or antagonistic ways. In the high frequency visible-UV wavelength regime, the molecule feels an optical cycle-averaged force field. Its dynamics is described through a Floquet representation based on light-induced potentials. The strong radiative interaction generally facilitates fragmentation through the Bond Softening (BS) process, which results from the lowering of some potential barriers accommodating shape resonances. More unexpectedly, the dissociation may, under specific conditions, be delayed or even suppressed through the complementary, non-intuitive, Vibrational Trapping (VT) that occurs for Feshbach resonances supported by some “upper” adiabatic potentials. In the low frequency IR wavelength regime, a quasi-static adiabatic picture is appropriate. The molecular vibrational motion follows the field’s oscillations. An appropriate synchronization, either completely suppress potential barriers, or produces reflection of the wave packet on them. This is the Dynamical Dissociation Quenching (DDQ) mechanism. BS and VT have been well documented in the literature [1,2] whereas a first experimental confirmation has only recently been given for DDQ [3,4].

Measured (lower panel) and calculated (upper panel) kinetic energy distributions for two-colour XUV+IR dissociative ionization of H_2, making use of a 7fs (a) and a 35fs (b) IR pulses.

Our team is actively involved in the description of such mechanisms on one hand, and in their exploitation both for interpretative, control and imaging purposes, on the other hand, within a long-period collaboration frame with two Canadian labs (A. D. Bandrauk, University of Sherbrooke ; T. T. Nguyen-Dang, University of Laval). A variety of molecular processes ranging from photo fragmentation (ionization/dissociation), to alignment/orientation, electron diffraction, high order harmonic generation or attosecond pulse production are among our current research interests. Two recent examples deal with the hydrogen molecule :
(i) The figure illustrates the degree of accuracy we are reaching within a full comprehensive frame for two pump (XUV atto-pulse-train) – probe (delayed intense IR pulse) experiments [5] ;
(ii) The depiction of so called Zero-Width Resonances [6] and Exceptional Points [7] opens the way to control scenarios for a selective preparation of a given molecular vibrational level, including the possibility of obtaining ro-vibrationaly cold molecules.

[1] A. Giusti-Suzor, X. He, O. Atabek and F.H. Mies, Phys. Rev. Lett. 64, 515 (1990)
[2] P.H. Bucksbaum, A. Zavriyev, H.G. Muller and D.W. Schumacher, Phy. Rev. Lett. 64, 1883 (1990)
[3] F. Châteauneuf, T.T. Nguyen-Dang, N. Ouellet and O. Atabek, J. Chem. Phys. 108, 3974 (1998)
[4] H. Nikura, P.B. Corkum and D.M. Villeneuve, Phys. Rev. Lett. 90, 203601 (2003)
[5] F. Kelkensberg, C. Lefebvre, W. Siu, O. Ghafur, T.T. Nguyen-Dang, O. Atabek, A. Keller, V. Serov, P. Johnsson, M. Swoboda, A. L’Huillier, G. Sansone, M. Nisoli, E. Benedetti, F. Ferrari, F. Lépine, M.F. Kling and M.J.J. Vrakking, Phys. Rev. Lett. 103, 123005 (2009)
[6] O. Atabek, R. Lefebvre, C. Lefebvre and T.T. Nguyen-Dang, Phys. Rev. A 77, 043413 (2008)
[7] R. Lefebvre, O. Atabek, M. Sindelka and N. Moiseyev, Phys. Rev. Lett. 103, 123003 (2009)

Post-scriptum :

To learn more :
“Unstable States in Laser Assisted and Controlled Molecular Processes”, in Advances in Quantum Chemistry, by O. Atabek, R. Lefebvre and T.T. Nguyen-Dang

Unstable States - 5.2 Mo