Femtosecond carrier dynamics in photoexcited highly ordered pyrolytic graphite films

The ultrafast relaxation of photoexcited carriers in thin films of exfoliated highly ordered pyrolytic graphite are examined using the equal-pulse correlation technique. An extremely fast relaxation due to intraband carrier–carrier thermalization was observed at 15 ± 10 fs followed by intraband carrier–optical phonon interaction on the order of 175 ± 30 fs. A modulation in the absorption depth of 1.4% was observed in the samples from partial saturation due to Pauli blocking.

► The equal-pulse correlation technique was utilized to examine relaxation times. ► We measure the ultrafast relaxation of photoexcited carriers in HOPG thin films. ► Modulation in the absorption depth of HOPG films due to Pauli blocking was observed. ► Relaxations are attributed to carrier–carrier and carrier–phonon interactions. ► Graphene and HOPG films are viable saturable absorbers for mode-locked lasers.