Previous experiments on graphite and graphene reported that hot carriers transfer most of their energy to hot optical phonons within 500 fs713143839. They observed a quick buildup of G-phonon occupation through e-ph coupling320, but they were not able to clearly resolve the short-time delay region and identify which transition is dominant. Due to finite time resolution, the G-phonons generated directly from e-h recombination are supposed to appear at negative times. Given our 90 fs time resolution, the increase of phonon population would be detected at ~−35 fs (see the green dashed line in Fig. 1). The abrupt appearance of G-phonons near t = 0 therefore suggests that G-phonon emission occurs with a time delay. The presence of a time delay is also clear when the probe pulse is used without the pump. In this case photons in the early-time part of a probe pulse pump the system, and the photons coming later but still belonging to the same pulse serve as an excitation for Raman scattering (This process is called self-pumping20). Due to the short time duration of the probe pulse (~50 fs), self-pumping integrates the excitations within the first 35 fs, which suggests that G-phonons are emitted more than 35 fs after a pump pulse, not about 10 fs as expected from direct decay of e-h pairs into this phonon.