Methods and systems include generating one or more mid-infrared frequencies based at least upon electron transitions in one or more quantum cascade heterostructures. The quantum cascade heterostructures are concurrently configured with a significant second-order nonlinear susceptibility, a significant third-order nonlinear susceptibility, and an insignificant group velocity dispersion. A set of mid-infrared frequencies (that may include a frequency comb) is generated in the quantum cascade heterostructures based at least upon a four-wave mixing of the one or more mid-infrared frequencies. The four-wave mixing arises at least from the significant third-order nonlinear susceptibility and the insignificant group velocity dispersion. A set of terahertz frequencies (that may include a frequency comb) is generated in the quantum cascade heterostructures based at least upon a difference frequency generation from mid-infrared frequency pairs selected from the set of mid-infrared frequencies. The difference frequency generation arises at least from the significant second-order nonlinear susceptibility.