Anisotropic Coulomb explosion of C-60 irradiated with a high-intensity femtosecond laser pulse

C-60 vapor was irradiated with an intense femtosecond laser pulse (1x10(16) W/cm2 in 120 fs at a wavelength of 800 nm). Multiply charged carbon ions, up to C4+, were detected in the time-of-flight spectra. We have measured bo th energy and angular distributions with respect to the laser polarization direction for ions with different charge number. The kinetic energy of ions are distributed above 1 keV. The angular distribution measurement shows th at the highly charged ions of C3+ and C4+ are mostly distributed in the dir ections parallel to the laser polarization, and the C+ ions are slightly di stributed in the direction perpendicular to it. These observations clearly indicate that an anisotropic explosion takes place. The average energy of i ons with the different charge number is found to be proportional to the squ are of the charge number, while the maximum energy is proportional to the c harge number. Classical molecular dynamics simulations have been successful ly carried out reproducing not only the energy spectra but also the angular distributions of ions. The C3+ ions are shown to be produced by the cascad e hopping of electrons induced by the intense laser light. The simulations suggest that the most crucial process for the anisotropic Coulomb explosion of C-60 is not the electron impact ionization, but the cascade hopping of electrons. (C) 2000 American Institute of Physics. [S0021-9606(00)01208-3].