Generation of light through second-order nonlinear processes in quantum cascade lasers

We demonstrate efficient intracavity nonlinear interaction of laser modes in quantum cascade (QC) lasers with resonant nonlinear optical intersubband transitions. Sum-frequency and second-harmonic generation at 4.1 and 3.6 and 4.7 /spl mu/m wavelength has been demonstrated for a two-wavelength QC laser emitting at the fundamental wavelengths 7.1 and 9.5 /spl mu/m. In a structure optimized for second harmonic generation, we measure 1.5 /spl mu/W of nonlinear power at 3.7 /spl mu/m wavelength together with 930 mW of fundamental power at 7.5 /spl mu/m wavelength. The experimental results are in very good agreement with the calculations.