Abstract
High-efficiency THz generation in quasi-phase matched (QPM) optically-contacted GaAs (OC-GaAs) with near-Brewster angle pumping is studied numerically. The effeective non- linear coefficients deff for different incident angles and polarization directions are inves- tigated. Compared with the normal incident case, reflection loss of the pump energy at OC-GaAs interfaces can be dramatically reduced by propagating the pump at a near- Brewster angle (66.92 0). At 66.92 0, a maximum effective nonlinear coefficient 0.901 d14 with µro = 33.58 0 can be reached. The effect of the air-gap between adjacent OC-GaAs layers to the optimal QPM periods and e±ciency of THz generation are calculated. There- fore, in this paper, we propose a di®erent pumping configuration in which a TM-polarized wave is pumped near the Brewster angle of the OC-GaAs to reduce the reflection loss both from the surfaces and interfaces. Compared with the normal incident configura- tion used conventionally, the optimal QPM periods of the near-Brewster angle pumped configuration increases significantly and a large overall enhancement in the conversion e±ciency is achieved. In our study, the number of optimal QPM periods of OC-GaAs is increased significantly from 12 in the normal incident configuration to 25 in the near-Brewster angle pumped con‾guration, while the efficiency of THz generation is enhanced by more than 16 times.