Photoelectron Angular Distributions for Two-photon Ionization of Helium by Ultrashort Extreme Ultraviolet Free Electron Laser Pulses

Abstract

Phase-shift differences and amplitude ratios of the outgoing $s$ and $d$ continuum wave packets generated by two-photon ionization of helium atoms are determined from the photoelectron angular distributions obtained using velocity map imaging. Helium atoms are ionized with ultrashort extreme-ultraviolet free-electron laser pulses with a photon energy of 20.3, 21.3, 23.0, and 24.3 eV, produced by the SPring-8 Compact SASE Source test accelerator. The measured values of the phase-shift differences are distinct from scattering phase-shift differences when the photon energy is tuned to an excited level or Rydberg manifold. The difference stems from the competition between resonant and non-resonant paths in two-photon ionization by ultrashort pulses. Since the competition can be controlled in principle by the pulse shape, the present results illustrate a new way to tailor the continuum wave packet.

5 pages, 1 table, 3 figures

References in corpus (6)

• Theory of attosecond delays in laser-assisted photoionization
• Double core hole production in N2: Beating the Auger clock
• Phase Measurement of Resonant Two-Photon Ionization in Helium
• Experimental Verification of the Chemical Sensitivity of Two-Site Double Core-Hole States Formed by an X-ray FEL
• Coherent strong-field control of multiple states by a single chirped femtosecond laser pulse
• Competition of resonant and nonresonant paths in resonance-enhanced two-photon single ionization of He by an ultrashort extreme-ultraviolet pulse

Cited by in corpus (8)

• Atomic, molecular and optical physics applications of longitudinally coherent and narrow bandwidth Free-Electron Lasers
• Maximum Elliptical Dichroism in Atomic Two-Photon Ionization
• Photoelectron distribution of non-resonant two-photon ionization of neutral atoms
• Breakdown of the electric dipole approximation at Cooper minima in direct two-photon ionisation
• Theoretical study of pulse delay effects in the photoelectron angular distribution of near-threshold EUV+IR two-photon ionization of atoms
• Photoelectron Angular Distributions of Nonresonant Two-Photon Atomic Ionization Near Nonlinear Cooper Minima
• Angle-resolved non-resonant two-photon single ionization of argon using 9.3 eV photons produced via high harmonic generation
• Relativistic effects in the non-resonant two-photon K-shell ionization of neutral atoms