在模擬計算上分析使用入射光其入射方向在接近布魯斯角時，配合光學接觸砷化鎵此方法所產生的兆赫信號可以大量提高信號轉換效率。研究入射光入射方向和入射光極化方向對於有效非線性係數的影響。與傳統垂直入射方法相比，當入射光入射方向傾斜為66.92度，對於入射光能量表面反射率將會被降低以提高穿透率。當入射方向調整為66.92度，我們必須旋轉砷化鎵到達 33.58度才能得到最大的有效非線性係數。而在推疊每ㄧ片砷化鎵晶體過程中，所產生的空氣夾層厚度與最大的兆赫信號轉換效率及最佳效率的砷化鎵片數的影響，在此也會詳細討論計算。因此，在這篇論文中，我們提出使用橫磁場波極化方向光以接近布魯斯特角入射光學接觸砷化鎵來降低表面各片晶片的反射率。比較起垂直入射使用的方法，使用接近布魯斯特角入射光不但可以增加最佳效率的砷化鎵片數更可以增加起兆赫信號轉換效率。
在我們的研究中，對於傳統垂直入射光學接觸砷化鎵方法的最佳效率砷化鎵片數是12層週期，而使用入射方向傾斜為66.92度的光學接觸砷化鎵方式來產生兆赫信號，最佳效率的砷化鎵片數可以提高到25層週期，比較起兆赫信號轉換效率更可以增進至少16倍。

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.

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