Fig. 5

Ultrafast THz spectra by wavelength-selective pump from THz to visible. THz spectra for several pump photon energies: a 4 meV, b 248 meV, c 354 meV, d–f 950 meV, and e, g 1550 meV at Δt_pp = 1 ps. Figures for Δσ₁ and Δε₁ have the same x and y axis ranges, respectively, for fair comparison. The THz spectra for a 4 meV, b 248 meV, and c 354 meV pump can be fitted well by keeping the SS and BS carrier densities constant (Δn_SS = 0 and Δn_BS = 0) and only changing the scattering rates of SS and BS. However, the THz spectra cannot be fitted in the same way for d 950 meV and e 1550 meV pump. Instead, they have to be fitted by changing both the carrier densities (Δn_SS > 0 and Δn_BS > 0) and the scattering rates of SS and BS, as shown in f and g