Figure 2: Ultrafast nonlinear optical properties of Cd₃As₂ films with 400 nm thickness.

(a) The non-degenerate ultrafast pump-probe results with the probe wavelength varying from 3 to 6 μm, and red solid lines correspond to a mono-exponential fit for τ_nondeg. (b) Fitted relaxation time constants τ versus probing wavelengths for both the degenerate (black and red points) and non-degenerate (blue points) measurements. (c) The nonlinear absorption at a wavelength of 3 μm (black points) and fitting with a simple saturation model (red line), T(I)=1−ΔT × exp(−I/I_sat)−T_ns, where I, ΔT, I_sat and T_ns are the input intensity, modulation depth, saturation intensity and non-saturable absorbance, respectively. A modulation depth of 4.4% and a saturation intensity of ∼0.78 GW cm⁻² are obtained. The horizontal black line is the base line.