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Time dynamics of photoexcited electron-hole pairs is important for a numberof technologies, in particular solar cells. We combined ultrafast pump-probeRaman scattering and photoemission to directly follow electron-hole excitationsas well as the G-phonon in graphite after an excitation by an intense laserpulse. This phonon is known to couple relatively strongly to electrons.Cross-correlating effective electronic and phonon temperatures places newconstraints on model-based fits. The accepted two-temperature model predictsthat G-phonon population should start to increase as soon as excitedelectron-hole pairs are created and that the rate of increase should not dependstrongly on the pump fluence. Instead we found that the increase of theG-phonon population occurs with a delay of $\sim$65 fs. This time-delay is alsoevidenced by the absence of the so-called self-pumping for G phonons. Itdecreases with increased pump fluence. We show that these observations imply anew relaxation pathway: Instead of hot carriers transferring energy toG-phonons directly, the energy is first transferred to optical phonons near thezone boundary K-points, which then decay into G-phonons via phonon-phononscattering. Our work demonstrates that phonon-phonon interactions must beincluded in any calculations of hot carrier relaxation in optical absorberseven when only short timescales are considered.

Novel Electron-Phonon Relaxation Pathway in Graphite Revealed by Time-Resolved Raman Scattering and Angle-Resolved Photoemission Spectroscopy