Electron Impact Ionization in the Presence of a Laser Field: A Kinematically Complete (n��e, 2e) Experiment (original) (raw)
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We characterize the unusually large current density and its time structure as seen by the ion following ionization. To do this, we use H 2 molecules in a low-density gas as a molecular clock. As ionization simultaneously forms two wave packets—one a vibrational wave packet moving on the H 2 þ (X 2 S g þ) surface; the other, the electron wave packet that we wish to study—ionization starts the vibrational clock in H þ 2 : We choose H þ 2 as the molecular clock because of the speed of its vibrational wave packet, and because all excited states of H þ 2 directly dissociate. By choosing the molecular axis perpendicular to the laser electric field, we decouple the X 2 S þ g and A 2 S þ u surfaces in H þ 2 ; ensuring that the clock remains accurate in the presence of the field. To read the clock, we observe the kinetic energy of the protons produced by inelastic scattering when the electron recollides with the parent ion. 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