School of Electronic and Electrical Engineering, University of Leeds, Leeds, United Kingdom.
J Chem Phys. 2011 Apr 7;134(13):134304. doi: 10.1063/1.3575201.
We report terahertz (THz) diffuse reflectance measurements of bulk powdered samples at a frequency of 2.83 THz using a narrowband quantum cascade laser. Samples studied comprise polydisperse powders with absorption coefficients extending over two orders of magnitude from ∼3 cm(-1) to >200 cm(-1). Diffuse reflectance measurements are used to obtain the effective absorption coefficient of these samples from the backscattering cross-section, predicted under the quasi-crystalline approximation (QCA) in the T-matrix formulation and in conjunction with the Percus-Yevick pair distribution function. Results are compared with effective absorption coefficients obtained from THz time-domain spectroscopy measurements on pressed pellet samples, and show good agreement over the range of effective absorption coefficients studied. We observe that the backscattering cross-section predicted under the QCA is strongly dependent on both the real and imaginary components of the complex permittivity of the sample, and we show that reliable determination of the absorption coefficient from diffuse reflectance measurements therefore requires knowledge of the sample's refractive index. This work demonstrates the applicability of diffuse reflectance measurements, using a THz frequency quantum cascade laser, to the high-resolution spectroscopic analysis of bulk powdered samples at THz frequencies.
我们报告了使用窄带量子级联激光器在 2.83 THz 频率下对块状粉末样品进行太赫兹（THz）漫反射测量的结果。研究的样品包括具有吸收系数的多分散粉末，吸收系数从约 3 cm(-1)扩展到>200 cm(-1)，跨越两个数量级。漫反射测量用于从后向散射截面获得这些样品的有效吸收系数，该截面是在准晶近似（QCA）下在 T 矩阵公式中预测的，并与 Percus-Yevick 对分布函数结合使用。结果与压片样品的太赫兹时域光谱测量得到的有效吸收系数进行了比较，在研究的有效吸收系数范围内表现出良好的一致性。我们观察到，QCA 下预测的后向散射截面强烈依赖于样品复介电常数的实部和虚部，因此我们表明，从漫反射测量可靠地确定吸收系数需要知道样品的折射率。这项工作证明了使用太赫兹频率量子级联激光器进行漫反射测量在太赫兹频率下对块状粉末样品进行高分辨率光谱分析的适用性。
