Fig. 5: Schematic diagram of photoexcited carriers and phonons evolving in 2H-MoTe₂ during a time window of nanoseconds.

Upon photoexcitation, the carriers thermalize within 100 fs. Subsequently, the hot carriers cool down via intravalley scattering within a picosecond and intervalley scattering within several picoseconds, accompanied with the emissions of A_1g OP at the BZ center and APs at the BZ border, respectively. Both the emitted SCPs undergo the phonon bottleneck. Then the anharmonic coupling with SCPs excites the low-frequency phonons in several tens of picosecond. The FS specimen establishes a quasi-thermal-equilibrium and is reheated by the indirect recombination in a duration of one nanosecond, followed by a cooling procedure through thermal diffusion within the specimen, which lasts a few nanoseconds. The heat dissipation in the CS specimen is significantly accelerated due to the thermal diffusion towards the substrate, which finishes in one nanosecond.