Photoelectron angular distributions of low-order above-threshold ionization of Xe in the multiphoton regime

Abstract

We present high-resolution two-dimensional momentum distributions and energy-angular distributions of photoelectrons from xenon atoms, ionized by an 800-nm, 25-fs linearly polarized laser at intensities of (1.8--4.4) \ifmmode\times\else\texttimes\fi{} 10${}^{13}$ W/cm${}^{2}$. The angular distributions of low-energy photoelectrons exhibit pronounced intensity-dependent features. The photoelectron angular distributions (PADs) of nonresonant ionization, Freeman resonance, and main order above-threshold ionization at different laser intensities are analyzed. We have characterized the PADs of above-threshold ionization up to the fourth order and have confirmed the angular momentum selection rule of $\ensuremath{\Delta}l=1$ for above-threshold ionization at all laser intensities. We observe that the channel of nine-photon resonant ionization has switched to a ten-photon process but nine-photon nonresonance still remains for xenon.