太赫兹( THz)量子级联激光器( QCL)是理想的固态 THz源，其出射光束的远场特性是 THz QCL研究中重要的一部分。实验上， THz QCL的远场光斑常呈多瓣或环形结构，用一般的衍射理论难以解释，为此把激光器看成辐射天线，利用电磁场理论，推导了单面金属波导 THz QCL辐射远场场分布和光强分布基本公式。对具有典型参数的 THz QCL的远场分布进行了计算。数值结果表明: 辐射远场光强分布是不对称的环形结构，且随着激光器的腔长变长，环逐渐变密。可见， THz QCL的天线模型给出了与实验观察一致的结果，说明天线模型更适合于 THz QCL远场光束的分析。

Terahertz(THz) Quantum Cascade Laser(QCL) is an ideal solid-state THz source. Investigating the far-field behavior of the output beam is an important part of the research of THz QCL. In the experiment, the THz QCL far field spot is often multi-petaled or in ring structure, which is difficult to explain by using the general diffraction theory. For this reason, considering the laser as a radiating antenna, according to the electromagnetic field theory, basic formulas of the electric field and intensity distributions of the radiation far-field of the single-metal waveguide THz QCL are derived. The far-field distribution of THz QCL with typical parameters are calculated. The numerical results show that far-field intensity distribution is in an asymmetric ring structure, and the ring becomes thicker as the laser cavity length increases. It can be seen that the THz QCL antenna model gives the same results as the experimental observation, which shows that the antenna model is more suitable for the analysis of the THz QCL far field beam.