Figure 1

(Color online) Raman spectra of the $G$-mode phonons in graphite with and without simultaneous pump excitation. The main figure shows the anti-Stokes scattering; the inset, the Stokes-scattering response. The solid lines are fits to a Gaussian line shape, with a width determined by the probe-laser spectrum.Reuse & Permissions

Figure 2

(Color online) Temporal dynamics of the $G$-mode phonons as a function of delay time following pump excitation. (a) Experimental anti-Stokes Raman intensity, which is proportional to the phonon mode population $n_G$. The solid line represents exponential decay with a time constant of 2.2 ps convoluted with the instrumental response. The absolute calibration of $n_G$, as discussed in the text, is based on the enhancement of the Stokes Raman signal. (b) Measured shifts of the $G$-mode frequency. The error bars are derived from fits like those in Fig. 1. The solid line is based on the model of the temperature dependence of the self-energy described in the text. (c) Temperature of the $G$-mode phonons inferred from the mode population in (a). At negative delay, the temperature is higher than room temperature. This increased temperature arises from self-pumping by the probe pulse.Reuse & Permissions

Figure 3

(Color online) Raman shift for different electronic temperatures. The data points are obtained from Figs. 2b, 2c for delay times $>0.2\text{ps}$. The solid line is the result of the calculation of the phonon self-energy, as presented in the text, for an electron-phonon coupling strength of $\lambda =0.0064$. The apparent oscillatory behavior of the data points could not be reproduced in other measurements and is attributed to experimental uncertainty.Reuse & Permissions