2ND-HARMONIC GENERATION INVOLVING VALENCE-SUBBAND TRANSITIONS IN P-DOPED GAAS ALXGA1-XAS QUANTUM-WELLS/

We present second-harmonic generation experiments in p-doped asymmetri cally stepped quantum wells using the emission of a free-electron lase r in the wavelength interval between 13 and 18 mu m. The wells are des igned such that the three fewest valence-subbands are about equally sp aced. We measured the angular and frequency dependence of the second-h armonic signal excited by intense laser irradiation chosen to be nearl y resonant with the transitions between the three lowest valence subba nds. We see evidence of the optical second-order susceptibility compon ents chi(xxz)((2)), chi(zxx)((2)) and chi(zxy)((2)), chi(xyz)((2)) in the quantum wells and determine their enhancement with respect to chi( xyz)((2)) of bulk GaAs.