In this paper, a quasi-optical mode converter for terahertz imaging is presented. This design is based on a 0.22 THz TE03 gyrotron oscillator. It includes a Vlasov launcher, an elliptical reflector and a parabolic reflector, which is used to convert TE03 cylindrical waveguide mode to a Gaussian-like beam. The quasi-optical system is analyzed in terms of geometric optics theory and the vector diffraction theory. Numerical optimization code is programmed by MATLAB software for analyzing the quasi-optical system. Simulation results show that the power transmission efficiency of the operating cavity mode to a fundamental Gaussian distribution is 82.14%, the output Gaussian beam can be propagated over 0.8 m without divergence and the scalar Gaussian mode content is 98.2%. A cold test experiment platform is built up to verify the design based on numerical calculation. In experiment, the scalar Gaussian mode content of 97.0% is measured which shows good agreement with numerical calculation.

中文翻译：

---

太赫兹成像陀螺准光模转换器的研究

在本文中，提出了一种用于太赫兹成像的准光模式转换器。此设计基于 0.22 THz TE03 回旋振荡器。它包括一个 Vlasov 发射器、一个椭圆形反射器和一个抛物面反射器，用于将 TE03 圆柱波导模式转换为类高斯光束。从几何光学理论和矢量衍射理论的角度对准光学系统进行了分析。数值优化代码由MATLAB软件编写，用于分析准光学系统。仿真结果表明，工作腔模式对基本高斯分布的功率传输效率为82.14%，输出高斯光束可以无发散地传播超过0.8 m，标量高斯模式含量为98.2%。基于数值计算，搭建冷试实验平台对设计进行验证。实验中测得的标量高斯模含量为97.0%，与数值计算吻合良好。