(a) Non-degraded ultrafast pump-probe results at probe wavelengths between 3 μ m and 6 μ m , and solid red line corresponding to single exponential fit of τ nondeg . (b) Fitted plots of relaxation time constant τ versus probing wavelength for both degenerate (black and red points) and non-degenerate (blue points) measurements. (c) Nonlinear absorption at wavelength 3 μ m (black points) and fitting with simple saturation model (red line). This figure is adapted from Ref. [40], Nature Publishing Group.