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A new ultrahigh vacuum-compatible (∼ 10-11 mbar) “reaction microscope” was built to investigate multiple ionization of atoms and molecules in ultra-short (23 fs), intense laser pulses (1014 – 1016 W/cm2, 795 nm) . In first experiments ion momentum distributions for single and double ionization of noble gas atoms in the nonsequential and sequential intensity regime were measured using linearly polarized laser pulses. The apparatus is currently improved to perform measurements under even lower residual gas pressures (< 10-13 mbar). Furthermore, the new apparatus is ideally suited for future studies on dissociation and Coulomb explosion of molecules. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

Double ionization of helium in collisions with 6 MeV protons (vP = 15.5 a.u.) has been explored in a kinematically complete experiment using a so-called “reaction microscope”. For the first time fully differential cross sections for positively charged particle impact have been obtained and compared to previous (e,3e) results with 2 keV electrons (vP = 12 a.u.). Differences have been found in the angular distribution of the two emitted electrons, which originate from projectile charge effects that are not considered in the first Born approximation. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

COLTRIMS (COLd Target Recoil-Ion Momentum Spectroscopy) was used to measure the vector momentum distribution of Ne[sup n+] (n=1,2,3) ions formed in ultrashort (30 fsec) high-intensity (approx. 10[sup 15] W/cm[sup 2]) laser pulses with center wavelength at 795 nm. To a high degree of accuracy the length of the Ne[sup n+] ion momentum vector is equal to the length of the total momentum vector of the n photoelectrons released, with both vectors pointing into opposite directions. At a light intensity where non-sequential ionization of the atom dominates the Ne[sup 2+] and Ne[sup 3+] momentum distributions show distinct maxima at 4.0 a.u. and 7.5 a.u. along the polarization axis of the linearly polarized light beam. First, this is a clear signature of non-sequential multiple ionization. Second, it indicates that instantaneous emission of two (or more) electrons at electric field strength maxima of the light wave can be ruled out as main mechanism of non-sequential strong-field multiple ionization. In contrast, this experimental result is in accordance with the kinematical constraints of the “rescattering model”. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]