Detailed analysis of second-harmonic generation near 10.6 μm in GaAs/AlGaAs asymmetric quantum wells

Abstract

We report on the observation of resonant intersubband second-harmonic generation in asymmetric GaAs/AlGaAs quantum wells using a cw or Q-switched tunable CO2 laser as the pumping source. The dependence of the second-harmonic intensity with the pump photon wavelength is presented for the first time. A Lorentzian-like second-harmonic line shape is found with a maximum at 10.9 μm and a linewidth of 0.4 μm (4.1 meV). These results are in good agreement with theoretical predictions. The expected quadratic dependence of the second-harmonic conversion efficiency with pump intensity is well verified for intensities up to 150 kW/cm2. The calibrated second-harmonic power reaches 0.13 μW for a cw pump power of 0.8 W. The value of 7.2×10−7 m/V deduced for the second-order nonlinear susceptibility is about 1900 times greater than that found in bulk GaAs.