Photoexcited dynamics in tellurium probed by coherent phonons

We studied the photoexcited dynamics in tellurium films using ultrafast pump-probe spectroscopy. Photoexcitation with femtosecond laser pulses produces carriers that modify the interatomic potential and thus excite coherent phonons. The phonon frequency strongly depends on the carrier density and the lattice temperature. We estimated the carrier density and the corresponding electronic bond softening using the diffusion equation. We also measured the phonon dynamics at different temperatures from 80 to 500 K. Based on these measurements, the lattice temperature within 1 ns after the pump pulse can be estimated using the frequency of the coherent phonons, excited by a second pump pulse. In addition, we modified the two-temperature model to simulate the dynamics of the carrier density, carrier temperature, lattice temperature, and phonon motion at different depths.