Figure 3

Typical ultra-broadband MIR ΔR/R spectra with fitting curves, taking account of free carrier absorption (FCA) and surface state transition (SST). ΔR/R as a function of the wavenumber for different delay times for (a) Bi₂Te₂Se and (b) Sb₂TeSe₂, using a pump fluence of 101  μJ/cm². The open circles represent the experimental data and each ΔR/R spectrum is shifted for clarity. The red lines are the fitting curves with a the Drude model and b the Drude-SST-Kubo model (δ_ω = −690 cm⁻¹). The insert in a shows the Moss-Burstien shift, as indicated by the arrow. Between the top solid line and the bottom solid line are the spectra that are respectively obtained by averaging the data from 0–1 (red), 1–2 (orange), 2–3 (bright green), 3–4 (green) and 4–5 (blue) ps.