Fig. 1. (a) Schematic diagram of MLG on SiO₂ substrate; (b) schematic diagram of BLG film on SiO₂ substrate; (c) Raman spectra of MLG and BLG.

Fig. 2. (a) Photoinduced THz conductivity of MLG and BLG as a function of the rising time at 1.91 eV, 160 µJ/cm²; (b) photoinduced THz conductivity of MLG and BLG as a function of the delay time at 1.91 eV, 160 µJ/cm².

Fig. 3. (a)–(c) Relaxation process of MLG (black) and BLG (red) as a function of pump fluence at different photon energies; (d) relaxation process of MLG (black) and BLG (red) as a function of photon energy at the same pump fluence.

Fig. 4. (a)–(c) Optical-induced THz conductivity peak value |Δσ| of MLG (black) and BLG (red) under different photon energies as a function of pump fluence; (d) ultrafast hot carrier cooling process of MLG and ultrafast heating and hot carrier cooling process of BLG. Diagrams of ultrafast processes and relaxation dynamics involving optical pumping (straight arrows), electron scattering (curled arrows), and optical phonon scattering (vertical blue wiggled arrows). Filled (open) circles signify electrons (holes). (e) Schematic diagram of the ultrafast dynamics in graphene after photoexcitation.

Fig. 5. (a), (b) Extracted frequency dependence of the THz conductivity at delay times of 0 ps and 2 ps for MLG, solid lines show the fit of the complex conductivity to a Drude model; (c), (d) extracted frequency dependence of the THz conductivity at delay times of 0 ps and 2 ps for BLG, solid lines show the fit of the complex conductivity to a Drude model.

Table 1. The Heating Parameter η