Quantum state-resolved probing of strong-field-ionized xenon atoms using femtosecond high-order harmonic transient absorption spectroscopy

Femtosecond high-order harmonic transient absorption spectroscopy is used to resolve the complete |j,m> quantum state distribution of Xe+ produced by optical strong-field ionization of Xe atoms at 800nm. Probing at the Xe N_4/5 edge yields a population distribution rho_j,|m| of rho_3/2,1/2 : rho_1/2,1/2 : rho_3/2,3/2 = 75 +- 6 : 12 +- 3 : 13 +- 6 %. The result is compared to a tunnel ionization calculation with the inclusion of spin-orbit coupling, revealing nonadiabatic ionization behavior. The sub-50-fs time resolution paves the way for table-top extreme ultraviolet absorption probing of ultrafast dynamics.