Transverse Electric and Transverse Magnetic Active IntersubbandTransitions in CaAs/AlGaAs Step Quantum Well

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