Figure 3: Ultrafast THz Snapshots of formation pathways of excitonic Rydberg states.

(a) The THz response functions (red dots) measured under 790 nm wavelength and 550 μJ cm⁻² fluence, at T=8 K and pump probe delay Δt=60 ps. The fit (black lines), based on the analytical model of equation (1), is the sum of 1s→2p (dashed red lines), 1s→3p (dashed green lines) and unbound e-h carriers (dashed blue lines). (b,c) Photoinduced conductivity changes Δσ₁(ω) at several pump-probe delays and T=8 K after excitation at 790 nm (550 μJ cm⁻² fluence) and 399 nm (120 μJ cm⁻² fluence), respectively. The shaded circles are the effective transition strength , extracted from photoinduced internal quantum transitions of excitons. The pump fluences are chosen to induce approximately equivalent for both excitations which allows to underpin their distinctly different rise times.