太赫兹时域光谱(THz-TDS)技术给人们提供了一种快速和准确地确定材料在太赫兹波段光学参数的工具。由于材料的厚度对其折射率的提取精度影响很大，而材料的厚度通常不能够准确地测量，为了避免测量厚度误差给确定光学参数结果带来的影响，发展能够同时确定样品的厚度和折射率的方法至关重要。由于材料内部的往返反射信号较弱，对Duvillaret等提出的方法在计算频段和迭代算法上进行了一些改进，使得计算结果更加准确，操作更加方便、快捷。并对两种典型材料聚乙烯和硅片的厚度和折射率进行了提取，以验证这种方法的有效性。

Terahertz time- domain spectroscopy provides us a powerful tool to carry out a fast and accurate measurement of optical constants of materials in terahertz range. The thickness determination of sample has a large influence on extracting the refractive index of materials. At the same time, the thickness of sample is generally difficult to be accurately measured. In order to avoid the influence from the measurement error of sample thickness on the determined refractive index, it is useful to develop a method which simultaneously determines the thickness and refractive index of sample. Due to the roundtrip reflected signal is weaker, the method presented by Duvillaret from the aspects of calculated frequency range and iterative algorithm is improved, making the calculated results more accurate and the operation more convenient. The thickness and refractive index of polyethylene and silicon wafer are determined as an example so that to verify the effectiveness of this method.