title: Monitoring molecular dynamics using coherent electrons from high harmonic generation.
abstract: We report a previously undescribed spectroscopic probe that makes use of electrons rescattered during the process of high-order harmonic generation. We excite coherent vibrations in SF(6) using impulsive stimulated Raman scattering with a short laser pulse. A second, more intense laser pulse generates high-order harmonics of the fundamental laser, at wavelengths of approximately 20-50 nm. The high-order harmonic yield is observed to oscillate, at frequencies corresponding to all of the Raman-active modes of SF(6), with an asymmetric mode most visible. The data also show evidence of relaxation dynamics after impulsive excitation of the molecule. Theoretical modeling indicates that the high harmonic yield should be modulated by both Raman and infrared-active vibrational modes. Our results indicate that high harmonic generation is a very sensitive probe of vibrational dynamics and may yield more information simultaneously than conventional ultrafast spectroscopic techniques. Because the de Broglie wavelength of the recolliding electron is on the order of interatomic distances, i.e., approximately 1.5 A, small changes in the shape of the molecule lead to large changes in the high harmonic yield. This work therefore demonstrates a previously undescribed spectroscopic technique for probing ultrafast internal dynamics in molecules and, in particular, on the chemically important ground-state potential surface.
authors.affiliation: Department of Physics, JILA, and National Science Foundation Engineering Research Center in Extreme-Ultraviolet Science and Technology, University of Colorado and National Institute of Standards and Technology, Boulder, CO 80309-0440, USA.
authors.forename: Nicholas L
authors.initials: NL
authors.lastname: Wagner
authors.forename: Andrea
authors.initials: A
authors.lastname: Wüest
authors.forename: Ivan P
authors.initials: IP
authors.lastname: Christov
authors.forename: Tenio
authors.initials: T
authors.lastname: Popmintchev
authors.forename: Xibin
authors.initials: X
authors.lastname: Zhou
authors.forename: Margaret M
authors.initials: MM
authors.lastname: Murnane
authors.forename: Henry C
authors.initials: HC
authors.lastname: Kapteyn
mesh_terms: D003198:Computer Simulation; D004583:Electrons; D005583:Fourier Analysis; D005740:Gases; D007834:Lasers; D008968:Molecular Conformation; D017785:Photons; D012542:Scattering, Radiation; D013052:Spectrometry, X-Ray Emission; D013059:Spectrum Analysis, Raman; D013459:Sulfur Hexafluoride / Q000737:chemistry; D013997:Time Factors; D014732:Vibration
chemical_list: D005740:Gases; D013459:Sulfur Hexafluoride