Abstract: Apparatus and methods for generating radiation via difference frequency generation (DFG). In one exemplary implementation, a quantum cascade laser (QCL) has a significant second-order nonlinear susceptibility (?(2)) integrated in an active region of the QCL. The QCL is configured to generate first radiation at a first frequency ?1, second radiation at a second frequency ?2, and third radiation at a third frequency ?3=?1??2 based on difference frequency generation (DFG) arising from the nonlinear susceptibility. In one aspect, the QCL may be configured to generate appreciable THz radiation at room temperature.

Abstract: Apparatus and methods for generating radiation via difference frequency generation (DFG). In one exemplary implementation, a quantum cascade laser (QCL) has a significant second-order nonlinear susceptibility (?(2)) integrated in an active region of the QCL. The QCL is configured to generate first radiation at a first frequency ?1, second radiation at a second frequency ?2, and third radiation at a third frequency ?3=?1??2 based on difference frequency generation (DFG) arising from the non-linear susceptibility. In one aspect, the QCL may be configured to generate appreciable THz radiation at room temperature.