不等光程法太赫兹波段材料光学参数的精确测量

Accurate optical parameters measurement of different optical path in the terahertz range

近20年,太赫兹科学技术发展迅速,太赫兹波与物质之间的相互作用成为研究热点。理论推导并实验验证了一种提高太赫兹波段材料折射率、吸收系数等参数测量精度的方法。以两种厚度的高密度聚乙烯板(3.5 mm、5.0 mm)为样品,将不等光程测量法与常规太赫兹时域光谱测量方法进行比较,分别获得了0.5~2.5 THz频率范围的高密度聚乙烯的折射率和吸收系数,结果显示两种方法测量样品的折射率和吸收系数有较大的差异。常规法和不等光程法得到的折射率分别为1.505和1.483。常规法在1.465 THz附近出现一个峰值,而不等光程法得到的吸收系数在1.166 THz和2.431 THz出现特征吸收峰。证明不等光程法能更加精确提取材料光学参数,并可以揭示常规方法无法测得的材料特征吸收峰,为太赫兹波段精确测量材料光学参数提供了新的方法。

In the past two decades, with the rapid development of the terahertz science and technology, the interaction between terahertz pulse and material has attracted much more scientific interest. In this paper, an accurate optical parameters extracting method was theoretically derived and experimentally demonstrated, a HDPE sample was measured by two similarly experimental scheme with terahertz time- domain spectroscopy. To compare the results of the regular method and the different optical path （DOP） method, the refractive index and the absorption coefficient from 0.5-2.5 THz were obtained, respectively, and the results show that the refractive index and the absorption coefficient of measured sample are quite different. The refractive indexes obtained by regular method and DOP method are 1.505 and 1.483 respectively. The absorption coefficient measured by the regular method has a peak in 1.465 THz, while DOP method＇s absorption coefficient has two peaks both in 1.166 THz and 2.431 THz. The different optical path method can reveal the absorption peak of the materials which can＇t be revealed by the regular method, and provide a more precious measurement of material optical parameters.