Fig. 3. Far-from-equilibrium NIR transient reflectivity of 1T-TaS₂ at 80 K.

(A) Single-shot transient reflectivity measurements averaged over 100 shots at 80 K following photoexcitation with an 1.55-eV pump pulse over a wide range of excitation fluences. (B) The CDW amplitude mode strength normalized by the fluence (red) and the offset response (blue) extracted from the fits to (A) as a function of excitation fluence. At low fluence, the offset response is nearly zero and only appears above a critical threshold fluence of 0.55 mJ/cm², above which it rapidly increases with increasing fluence. For the CDW amplitude mode, the coherent response is strongest at low fluence and then drops steadily as the fluence is increased, nearly disappearing at the same threshold fluence. (C) Single-shot transient reflectivity measurements as a function of both interpump delays and pump-probe delays with three distinct fluence regimes: 0.4 + 0.4 mJ/cm² or low fluence regime, 1.1 + 1.1 mJ/cm² or medium fluence regime, and 2.2 + 2.2 mJ/cm² or high fluence regime. (D) The amplitude mode strength and (E) offset extracted from the fits to (C) for the three fluence regimes as a function of interpump delay. a.u., arbitrary units.