Breathing coherent phonons and caps fragmentation in carbon nanotubes following ultrafast laser pulses

The response of carbon nanotubes to femtosecond laser pulses is studied with a nonadiabatic simulation technique, which accounts for the evolution of electronic and ionic degrees of freedom, and for the coupling with the external electromagnetic field. As a direct result of electronic excitation, three coherent breathing phonon modes are excited: two radial vibrations localized in the caps and cylindrical body, and one longitudinal vibration coupled to the nanotube length. Under high absorbed energies (but below 2.9 eV/atom, the graphite's ultrafast fragmentation threshold), the resulting oscillatory motion leads to the opening of nanotube caps. Following the cap photofragmentation the nanotube body remains intact for the rest of the 2 ps simulation time.