太赫兹时域光谱技术的参数提取及其误差分析

Optical parameter extraction and error analysis of terahertz time domain spectrum detection

太赫兹时域光谱技术(THz-TDS)是通过分析携带介质信息(如振幅和相位等)的宽频带太赫兹脉冲,从而对材料内部信息进行提取的一种光谱检测方法。实验应用透射式的检测方式,对陶瓷基复合材料和硅胶材料进行检测。建立材料光学参数模型,提取了折射率和吸收系数的值,并绘制了折射率和吸收系数随频率变化的曲线图。结果显示,密度不同的陶瓷基复合材料的折射率各自稳定于常数1.11、1.14、1.16,厚度不同的硅胶的折射率为2.10,且折射率曲线不存在频率依赖性;而吸收系数对频率依赖性较强,但对于材料特性不同的样品的吸收明显不同。基于高斯误差理论,对实验中出现的系统误差进行数学识别与建模,分析了密度为2.8 g/cm3的陶瓷基复合材料光学参数的几种误差源的传播过程。折射率的标准差趋于平稳,吸收系数的标准差随频率变化明显,且标准差均在0.001量级,这对折射率和吸收系数等物理量的精确提取具有较大的意义。

Terahertz time-domain spectroscopy（THz-TDS） is a spectral detection method. The information of the material is measured through the broadband terahertz pulse carrying the medium information（such as amplitude and phase）. The ceramic matrix composites and silica gel materials were tested with the detection method of transmission. The optical parametric models of the material were established, and the values of the refractive index and the absorption coefficient were extracted. The curves of the refractive index and the absorption coefficient with frequency were plotted. The refractive index of the ceramic matrix composites with different density are respectively convergent to a constant of 1.11, 1.14 and 1.16, and the refractive index of silica gel with different thickness is 2.1, which is not dependent to frequency. While the frequency dependence of the absorption coefficient is evident, and the absorption of samples with different material properties is significantly different. Based on the Gaussian error theory, the errors of the optical parameters are simulated and modeled. The experimental results show that there are several error sources in the optical parameters of the ceramic matrix composites with density of 2.8 g/cm-3. The standard deviation of the refractive index and the absorption coefficient are obviously related to the frequency, and the standard deviation is in the order of 0.001, which is of great significance to the precise extraction of the physical parameters such as the refractive index and the absorption coefficient.