Čerenkov-type phase-matched second-harmonic emission from GaAs∕AlGaAs quantum-cascade lasers

Abstract

Second-harmonic (SH) emission in the form of Čerenkov-type phase-matched radiation has been measured for quantum-cascade lasers (QCLs) with built-in nonlinearities. The QCLs operate at 10.9μm wavelength and, due to material dispersion, show a high collinear phase mismatch, resulting in low SH external conversion efficiencies on the order of 2μW∕W2. Due to our waveguide design, we were able to couple out and measure the generated SH light in the form of Čerenkov-type phase-matched radiation from the substrate of the device. The SH power collected from the Čerenkov beam leads to an increased external conversion efficiency of ∼50μW∕W2.