Origins of Terahertz Difference Frequency Susceptibility in Midinfrared Quantum Cascade Lasers

A room-temperature (and thus cryogen-free) source of highly sought terahertz radiation relies on difference-frequency generation inside a dual-wavelength midinfrared quantum cascade laser (QCL). The authors develop a nonperturbative transport model to give fresh insight into this system's physical mechanisms of terahertz generation, including strategies to yield frequencies below 2 THz. Their analysis reveals significant contributions that were previously underappreciated. This approach may also address interesting physics in other QCL-based devices, including terahertz and midinfrared frequency combs.