Mapping Molecular Orbital Symmetry on High-Order Harmonic Generation Spectrum Using Two-Color Laser Fields

We have measured high-order harmonic generation spectra of D2, N2, and CO2 by mixing orthogonally polarized 800 and 400 nm laser fields. The intensity of the high-harmonic spectrum is modulated as we change the relative phase of the two pulses. For randomly orientated molecules, the phase of the intensity modulation depends on the symmetry of the molecular orbitals from which the high harmonics are emitted. This allows us to identify the symmetry of any orbital that contributes to high-harmonic generation, even without aligning the molecule. Our approach can be a route to imaging dynamical changes in three-dimensional molecular orbitals on a time scale as short as a few hundred attosecondsNous avons mesur\ue9 les spectres de g\ue9n\ue9ration d\u2019harmoniques d\u2019ordre \ue9lev\ue9 de D2, N2 et CO2 en m\ue9langeant des champs laser \ue0 polarisation orthogonale de 800 et de 400 nm. L\u2019intensit\ue9 du spectre \ue0 harmoniques \ue9lev\ue9es est modul\ue9e pendant que nous changeons la phase relative des deux impulsions. Dans le cas des mol\ue9cules orient\ue9es al\ue9atoirement, la phase de la modulation d\u2019intensit\ue9 est fonction de la sym\ue9trie des orbites mol\ue9culaires d\u2019o\uf9 les harmoniques \ue9lev\ue9es sont \ue9mises. Cela nous permet de d\ue9terminer la sym\ue9trie de toute orbite qui contribue \ue0 la g\ue9n\ue9ration des harmoniques \ue9lev\ue9es, m\ueame sans alignement des mol\ue9cules. Notre technique peut \ueatre une voie vers l\u2019imagerie des changements dynamiques dans des orbites mol\ue9culaires tridimensionnelle \ue0 une \ue9chelle temporelle de quelques centaines d\u2019attosecondes.Peer reviewed: YesNRC publication: Ye