TY - DATA T1 - Two-dimensional projection (left) of the momentum distribution of the outgoing photoelectrons from the TPI of helium (He) atoms at 20.3 eV photon energy, and the corresponding slice (right) through the retrieved 3D photoelectron momentum distribution obtained from an Abel inversion PY - 2013/08/13 AU - R Ma AU - S Yase AU - K Nagaya AU - K Ueda AU - A Yamada AU - H Fukuzawa AU - S Mondal AU - K L Ishikawa AU - K Motomura AU - Y Mizoguchi UR - https://iop.figshare.com/articles/figure/_Two_dimensional_projection_left_of_the_momentum_distribution_of_the_outgoing_photoelectrons_from_th/1012425 DO - 10.6084/m9.figshare.1012425.v1 L4 - https://ndownloader.figshare.com/files/1480247 KW - amplitude ratios KW - Abel inversion KW - photon energies KW - Rydberg manifold KW - sase KW - contribution KW - Photon energy KW - ionization KW - ev KW - 3 D photoelectron momentum distribution KW - continuum wave packet KW - femtosecond pulses KW - velocity map imaging spectrometer KW - tpi KW - helium atoms KW - photoelectrons KW - momentum distribution KW - continuum wave packets KW - pulse shape KW - Atomic Physics KW - Molecular Physics N2 - Figure 1. Two-dimensional projection (left) of the momentum distribution of the outgoing photoelectrons from the TPI of helium (He) atoms at 20.3 eV photon energy, and the corresponding slice (right) through the retrieved 3D photoelectron momentum distribution obtained from an Abel inversion. Abstract The two-photon ionization of helium atoms by ultrashort extreme-ultraviolet free-electron laser pulses, produced by the SPring-8 Compact SASE Source test accelerator, was investigated at photon energies of 20.3, 21.3, 23.0 and 24.3 eV. The angular distribution of photoelectrons generated by two-photon ionization is obtained using a velocity map imaging spectrometer. The phase-shift differences and amplitude ratios of the outgoing s and d continuum wave packets are extracted from the photoelectron angular distributions. The obtained values of the phase-shift differences are distinct from scattering phase-shift differences when the photon energy is tuned to a resonance with an excited level or Rydberg manifold. The difference stems from the co-presence of resonant and non-resonant path contributions in the two-photon ionization by femtosecond pulses. Since the relative contribution of both paths can be controlled in principle by the pulse shape, these results illustrate a new way to tailor the continuum wave packet. ER -