FIG. 4.

(a) Raw color-coded map of the transient reflectivity (ΔR/R) of La₂CuO₄ at 10 K as a function of probe photon energy and time delay between the pump and probe. The pump photon energy is set at 3.10 eV and the absorbed fluence is ∼4.4 mJ/cm². The pump and probe polarizations are parallel to the [100] and [001] crystallographic directions, respectively. (b) Rise of the temporal trace at 2.60 eV, integrated over 0.20 eV. (c) Temporal trace of ΔR/R at a probe photon energy of 2.00 eV, integrated over 0.40 eV. Inset: residuals from a multiexponential fit of temporal trace at 2.00 eV. (d) Fourier transform analysis of the residuals in the inset of panel (c). The symbols I, II, III, IV, and V identify the peaks corresponding to the ${\mathrm{A}}_{\mathrm{g}}$ phonon modes of the crystal.⁴⁰