Figure 5. Device performance at a fixed difference-frequency of 3.57 THz with 9 different combinations of ω₁ and ω₂ (indicated with 9 black dots in Fig. 4(d–f)).

Panels (a,b) show the power of mid-IR pump ω₁ and pump ω₂, respectively, as a function of current through the device. Inset in (b) shows the mid-IR emission spectra at pump current of 3.3 A. Panel (c) shows THz light-output-current characteristics of the device and (d) shows THz power output as a function of the product of the mid-IR pump powers, for 9 different combinations of ω₁ and ω₂.