Resonant Second-Order Nonlinear Optical Processes in Quantum Cascade Lasers

We demonstrate an efficient intracavity nonlinear interaction of laser modes in a specially adapted quantum cascade (QC) laser. A two-wavelength QC laser structure operating at 7.1 and 9.5 mum wavelength included cascaded resonant optical intersubband transitions in an intracavity configuration leading to resonantly enhanced sum-frequency and second-harmonic generation at 4.1 and 3.6 and 4.7 mum wavelength, respectively. Laser peak optical powers of 60 and 80 mW resulted in 30 nW of sum-frequency signal and 10-15 nW of second harmonic signal, both in good agreement with the theoretical calculations. Such compound materials, acting simultaneously as pumping source and mixing nonlinearity, may be optimized to achieve a huge resonant enhancement of the nonlinear optical power conversion efficiency in a compact, monolithic device.