Myers Tanya L, Brauer Carolyn S, Su Yin-Fong, Blake Thomas A, Tonkyn Russell G, Ertel Alyssa B, Johnson Timothy J, Richardson Robert L
Appl Opt. 2015 May 20;54(15):4863-75. doi: 10.1364/AO.54.004863.
We have recently developed vetted methods for obtaining quantitative infrared directional-hemispherical reflectance spectra using a commercial integrating sphere. In this paper, the effects of particle size on the spectral properties are analyzed for several samples such as ammonium sulfate, calcium carbonate, and sodium sulfate as well as one organic compound, lactose. We prepared multiple size fractions for each sample and confirmed the mean sizes using optical microscopy. Most species displayed a wide range of spectral behavior depending on the mean particle size. General trends of reflectance versus particle size are observed such as increased albedo for smaller particles: for most wavelengths, the reflectivity drops with increased size, sometimes displaying a factor of 4 or more drop in reflectivity along with a loss of spectral contrast. In the longwave infrared, several species with symmetric anions or cations exhibited reststrahlen features whose amplitude was nearly invariant with particle size, at least for intermediate and large size sample fractions: that is, ≳150 μm. Trends of other types of bands (Christiansen minima, transparency features) are also investigated as well as quantitative analysis of the observed relationship between reflectance versus particle diameter.
我们最近开发了经过验证的方法，用于使用商用积分球获得定量红外定向半球反射光谱。在本文中，分析了粒径对硫酸铵、碳酸钙、硫酸钠等几种样品以及一种有机化合物乳糖的光谱特性的影响。我们为每个样品制备了多个粒径级分，并使用光学显微镜确认了平均粒径。大多数物质根据平均粒径表现出广泛的光谱行为。观察到反射率与粒径的一般趋势，例如较小颗粒的反照率增加：对于大多数波长，反射率随粒径增加而下降，有时反射率下降4倍或更多，同时光谱对比度降低。在长波红外中，几种具有对称阴离子或阳离子的物质表现出剩余射线特征，其幅度几乎与粒径无关，至少对于中等和大粒径样品级分是如此，即≳150μm。还研究了其他类型波段（克里斯琴森极小值、透明特征）的趋势以及对观察到的反射率与粒径之间关系的定量分析。
