Direct femtosecond laser excitation of the 2p state of H by a resonant seven-photon transition in H{sub 2}{sup +}

We observe Lyman-{alpha} radiation produced by the direct excitation of H{sub 2}{sup +} by 23-fs 800-nm laser pulses. The laser pulse first ionizes H{sub 2} molecules and dissociates the ions through bond softening, leaving the molecules in the repulsive 2p{sigma}{sub u} state. The expanding H{sub 2}{sup +} ions enter a region of strong multiphoton coupling leading to a resonant seven-photon excitation of the 2s{sigma}{sub g} state. Finally, the 2s{sigma}{sub g} state dissociates into the H(2s) and H(2p) atomic limits. The latter state then decays through Lyman-{alpha} emission.