SHORT-WAVELENGTH (5.36-1.85-MU-M) NONLINEAR SPECTROSCOPY OF COUPLED INGAAS ALAS INTERSUBBAND QUANTUM-WELLS/

We report short wavelength second-harmonic generation (SHG) spectrosco py of asymmetric coupled In0.6Ga0.4As/AlAs quantum wells (QWs). The QW is designed to show maximum second-order nonlinear susceptibility chi ((2)) for SHG of 4 and 2 mu m wavelengths by single and double resonan ce effects, respectively. SHG spectroscopy across the midinfrared is m easured using both a CO2 and a free electron laser as pumps. The chi(( 2)) of the QW is extracted from interference of the second-harmonic fi elds from the QW and GaAs substrate, determined by the azimuthal depen dence of the SHG power. We measure chi((2)) of the QW for harmonic wav elengths between 5.36 and 1.85 mu m. This is the shortest wavelength S HG to date by any QW intersubband interaction. Good agreement of exper iment with theory for the dispersion of chi((2)) for both singly and d oubly resonant conversion is observed throughout the midinfrared. (C) 1994 American Institute of Physics.