High-harmonic probing of electronic coherence in dynamically aligned molecules.
We introduce and demonstrate a new approach to measuring coherent electron wave packets using high-harmonic spectroscopy. By preparing a molecule in a coherent superposition of electronic states, we show that electronic coherence opens previously unobserved high-harmonic-generation channels that connect distinct but coherently related electronic states. Performing the measurements in dynamically aligned nitric oxide molecules we observe the complex temporal evolution of the electronic coherence under coupling to nuclear motion. Choosing a weakly allowed transition to prepare the wave packet, we demonstrate an unprecedented sensitivity that arises from optical interference between coherent and incoherent pathways. This mechanism converts a 0.1% excitation fraction into a ∼20% signal modulation.
Laboratorium für Physikalische Chemie, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland.
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Kraus
Max Planck Institute for the Physics of Complex Systems, 01187 Dresden, Germany and Center for Free-Electron Laser Science, DESY, 22607 Hamburg, Germany.
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Zhang
Laboratorium für Physikalische Chemie, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland.
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Gijsbertsen
Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255, USA.
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Lucchese
Max Planck Institute for the Physics of Complex Systems, 01187 Dresden, Germany and Center for Free-Electron Laser Science, DESY, 22607 Hamburg, Germany.
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Rohringer
Laboratorium für Physikalische Chemie, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland.
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Wörner