Fig. 2. Temperature- and fluence-dependent propagation.

(A) FT power density as a function of the distance of the ring over which we average the signal from the center of the pump region. These data were collected using a pump fluence of 0.3 mJ/cm². The dataset for the 1-THz mode is magnified by a factor of 15 to improve its visibility. (B and D) Spatial dependence of the normalized FT power density for the 2.9-THz mode as a function of pump fluence (measured at room temperature) (B) and of temperature (each measured at a comparable fluence of ≃1.2 mJ/cm²) (D). The dashed line indicates the profile of the pump pulse. (C) HWHM of the phonon spatial extension as a function of the pump fluence for the 1- and 2.9-THz modes.