The effect of defects upon the dynamics of photo-excited carriers and coherent acoustic phonons was investigated by means of reflectivity measurements with fs time-resolution. Point defects were introduced by irradiating the graphite with 5keV He+ ions. The introduction of defects enhanced carrier relaxation by opening a decay channel via vacancy states. This competed with carrier–phonon scattering. Coherent phonon relaxation was also accelerated, due to additional scattering by defects. A linear fluence-dependence of the decay rate was attributed to the scattering of propagating acoustic phonons by single vacancies.

Ultrafast Carrier and Phonon Dynamics in Ion-Irradiated Graphite. K.Ishioka, M.Hase, M.Kitajima, K.Ushida: Applied Physics Letters, 2001, 78[25], 3965-7