Multiphoton Fragmentation of H₂⁺ at 800 nm
C. Schellhammer and H. Helm

Fakultät für Physik, Albert-Ludwigs Universität,
Hermann Herderstr. 3, 79104 Freiburg, Germany

e present a measurement of the kinetic energy spectrum of protons formed from mass selected H₂⁺ ions which are exposed to an intense femtosecond laser pulse at 800 nm. The molecular ions are prepared by five-photon ionization of neutral H₂, accelerated in an electric field, and subsequently exposed to the intense laser. This approach permits complete discrimination of proton fragments formed from neutral and from ionized molecular hydogen and permits the determination of the proton kinetic energy distribution with high precision.

Our experimental results are consistent with recent theoretical predictions by Walsh et al (Phys. Rev. A 58, 3922 1998) on the proton energy distribution of the molecuar ion at high laser intensity.