Ma, R Yase, S Nagaya, K Ueda, K Yamada, A Fukuzawa, H Mondal, S L Ishikawa, K Motomura, K Mizoguchi, Y Measured (thick red lines) and calculated (thin blue lines) photoelectron angular distributions (PADs) for the TPI of He <p><strong>Figure 2.</strong> Measured (thick red lines) and calculated (thin blue lines) photoelectron angular distributions (PADs) for the TPI of He. The experimental PADs are constructed from the β<sub><em>l</em></sub> values extracted from the Abel inversion procedure.</p> <p><strong>Abstract</strong></p> <p>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.</p> amplitude ratios;Photon energy;femtosecond pulses;ionization;tpi;photoelectron;helium atoms;continuum wave packets;Abel inversion procedure;sase;continuum wave packet;photon energies;pulse shape;pad;velocity map imaging spectrometer;Rydberg manifold;contribution;Atomic Physics;Molecular Physics 2013-08-13
    https://iop.figshare.com/articles/figure/_Measured_thick_red_lines_and_calculated_thin_blue_lines_photoelectron_angular_distributions_PADs_fo/1012426
10.6084/m9.figshare.1012426.v1