title: Two-photon resonant excitation of a doubly excited state in He atoms by high-harmonic pulses.
abstract: We experimentally demonstrate a two-color two-photon resonant excitation of the doubly excited 2p2 1S state in helium atoms by the combination of 19th and 21st harmonic photons of a Ti:sapphire laser. Production of the 2p2 1S state is confirmed by the experimental observation that the electron emission from this state does not depend on the direction of harmonic polarization. Our ab-initio theoretical results through the solution of time-dependent Schrödinger equation are consistent with the experimental results and confirm the first successful production of a doubly excited state by high-harmonic pulses.
authors.affiliation: Department of Applied Physics, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo 060-8628, Japan. sekikawa@eng.hokudai.ac.jp
authors.forename: Taro
authors.initials: T
authors.lastname: Sekikawa
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Okamoto
authors.forename: Eisuke
authors.initials: E
authors.lastname: Haraguchi
authors.forename: Mikio
authors.initials: M
authors.lastname: Yamashita
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakajima