Lawrence Berkeley National Laboratory

We present an experimental study on the photoionization dynamics of nonresonant one-color two-photon single valence ionization of neutral argon atoms. Using 9.3-eV photons produced via high harmonic generation and a three-dimensional momentum imaging spectrometer, we detect the photoelectrons and ions produced from nonresonant two-photon ionization in coincidence. Photoionization from the 3p orbital produces a photoelectron scattering wave function with p- and f-partial-wave components, which interfere and result in a photoelectron angular distribution with peak amplitude perpendicular to the vacuum ultraviolet polarization. The comparison between the present results and the two previous sets of theoretical calculations [Phys. Rev. A 44, 324 (1991)PLRAAN1050-294710.1103/PhysRevA.44.324, and J. Phys. B: At. Mol. Phys. 16, 2737 (1983)JPAMA40022-370010.1088/0022-3700/16/15/016] indicates that electron-electron correlation contributes appreciably to the two-photon ionization dynamics.