Appl Opt. 2021 Mar 10;60(8):2412-2421. doi: 10.1364/AO.414107.
A method for deriving the optical constants (/) of organic powdered materials using pressed pellets in the mid-infrared spectral range is introduced that combines variable angle spectroscopic ellipsometry and transmission spectroscopy. The approach is applied to anhydrous lactose, in which three different forms of pellets were pressed and measured: a pure lactose pellet and a mixed lactose/potassium bromide (KBr) pellet with a large analyte percentage were used for ellipsometric measurements, and a KBr transmission pellet with only a small analyte percentage was used for transmission measurements. The transmittance data provide an initial set of oscillators and improve the spectral fitting of weak absorption features (<0.01). Ellipsometric data for the pure and mixed pellets are then fit simultaneously to derive the final / values for lactose from 6000-400. An alternative method just using the ellipsometric data from the mixed pellet and the transmittance data is also presented and shows good agreement with the multi-sample analysis, providing a simpler method for powders that do not press easily into pure pellets. Finally, the derived optical constants were used to model the reflectance data, demonstrating a good match with the measured reflectance spectra if non-idealities are included.
本文提出了一种在中红外光谱范围内使用压制薄片将光学常数 (/ )从有机粉末材料中导出的方法，该方法结合了可变角度光谱椭圆偏振术和透射光谱。该方法应用于无水乳糖，其中压制并测量了三种不同形式的薄片：纯乳糖薄片和具有大分析物百分比的乳糖/溴化钾 (KBr) 混合薄片用于椭圆偏振测量，而仅具有小分析物百分比的 KBr 透射薄片用于透射测量。透过率数据提供了一组初始振荡器，并改善了弱吸收特征（<0.01）的光谱拟合。然后同时拟合纯和混合薄片的椭圆偏振数据，从 6000-400 导出乳糖的最终 / 值。还提出了一种仅使用混合薄片的椭圆偏振数据和透过率数据的替代方法，并且与多样本分析吻合良好，为不易压制成纯薄片的粉末提供了更简单的方法。最后，所得到的光学常数用于模拟反射率数据，如果包含非理想性，则与测量的反射率光谱很好地吻合。
