TRANSVERSE ELECTRIC AND TRANSVERSE MAGNETIC ACTIVE INTERSUBBAND TRANSITIONS IN GAAS ALGAAS STEP QUANTUM-WELL/

We have observed transverse electric (TE) and transverse magnetic (TM) intersubband infrared absorption peaks in GaAs/AlGaAs step multiquant um wells (SMQW). The energy splitting between TE and TM is 13 meV. The high conversion efficiency of second harmonic signal due to intersubb and transition in the GaAs/AlGaAs SMQW with a waveguiding surface-emit ting structure have been obtained. The second harmonic generation (SHG ) obeys wave vector conservation and propagates perpendicular to the w aveguide surface which shows that the nonlinear polarization field for SHG may be TE as well as TM active. The existence of strong surface-e mitting second harmonic signal also offers solid evidence of TE polari zation active intersubband transition in GaAs/AlGaAs SMQW structure.