Figure 3

Intensity of scattered radiation and corresponding lattice temperature at t = 225 ps.

(a) The measured Bragg peak intensity of the scattered radiation from across the sample surface. The values are plotted relative to the Bragg intensity without heating. This ratio is given by , where is the Debye-Waller factor. Here, k = 3.73 Å⁻¹ is the scattering wave number with its direction parallel to the c axis of the graphite lattice and is the out-of-plane rms deviation from the equilibrium ion positions. Since is a function of (see supplementary information), we can calculate the ion temperature from the measured decrease in the Bragg scattering intensity, as reported on the right axis of the plot. The shaded region corresponds to ion temperatures obtained by solving the two-temperature model (1) and (2) with an electron-phonon coupling constant of g = 0.45−0.8×10¹⁶ W K⁻¹ m⁻³. (b) Calculated spatial distribution of the lattice temperature within the graphite sample based on the measured decrease in Bragg scattering (best agreement with experimental data is obtained by assuming g = 0.6×10¹⁶ W K m.).