在自行搭建的双焦点太赫兹主动成像系统基础上，建立了与角度相关的拟合函数，并利用最小二乘拟合多项式的方法对拟合系数进行计算，成功将扫描轨迹的几何光学追迹计算过程简化成为二元函数计算。该系统为收发同路式像方旋转镜扫描。由于拟合自变量对太赫兹图像的影响很大，采用两种不同的拟合自变量进行计算，并且通过数值分析和成像结果分析比较两者的优劣。实验结果表明，当以旋转镜法向量的坐标分量作为拟合自变量时，计算扫描轨迹的速度减小至3 s/frame，且太赫兹图像非常准确。该系统实现了在约8 m处，50 cm×100 cm视场内达3 cm空间分辨率的快速精确成像。这为扫描式太赫兹快速成像系统提供了有价值的参考，对实时太赫兹安检、无损检测等领域有着实用意义。

We simulate the measurements of an active bifocal terahertz imaging system to reproduce the ability of the system to detect the internal structure of foams having embedded defects. Angular spectrum theory and geometric optics tracing are used to calculate the incident and received electric fields of the system and the scattered light distribution of the measured object. The finite-element method is also used to calculate the scattering light distribution of the measured object for comparison with the geometric optics model. The simulations are consistent with the measurements at the central axis of the horizontal stripe defects.