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Anomalous diffraction theory for arbitrarily oriented finite circular cylinders and comparison with exact T-matrix results

机译：任意取向有限圆柱体的反常衍射理论及其与精确T矩阵结果的比较

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A general method is developed to formulate extinction and absorption efficiency for nonspherical particles at arbitrary and random orientations by use of anomalous diffraction theory (ADT). An ADT for finite circular cylinders is evaluated as an example. Existing AD's for infinite cylinders at arbitrary orientations and for finite cylinders at the normal incidence are shown to be special cases of the new formulation. ADT solutions for finite cylinders are shown to approach the rigorous T-matrix results when the refractive indices approach unity. The importance of some physical processes that are neglected in the ADT approximation are evaluated by comparisons between ADT and rigorous calculations for different particle geometries. For spheres, van de Hulst's ADT and Mie theory are used, whereas the ADT that we present and T-matrix calculations are used for cylinders of different diameter-to-length ratios. The results show that the differences in extinction between ADT and exact solutions generally decrease with nonsphericity. A similar decrease occurs for absorption at wavelengths of relatively strong absorption. The influence of complex refractive index is evaluated. Our results suggest that ADT may provide a useful approximation in parameterization and remote sensing of cirrus clouds in the Christiansen bands where the real part of the refractive index approaches unity and/or where relative absorption is strong. (C) 1998 Optical Society of America. [References: 36]
机译：开发了一种通用方法，通过使用异常衍射理论（ADT）来确定任意和随机方向上非球形粒子的消光和吸收效率。以有限圆柱的ADT为例进行评估。新配方的特殊情况表明，任意方向上的无限圆柱体和法向入射时的有限圆柱体的现有AD都是特殊情况。当折射率接近于1时，有限圆柱体的ADT解决方案显示出接近严格的T矩阵结果。通过比较ADT和针对不同粒子几何形状的严格计算，可以评估ADT近似中忽略的某些物理过程的重要性。对于球体，使用van de Hulst的ADT和Mie理论，而我们介绍的ADT和T矩阵计算用于直径和长度比率不同的圆柱体。结果表明，ADT和精确解之间的消光差异通常随非球形度而减小。对于在相对强吸收的波长处的吸收，发生类似的下降。评估复数折射率的影响。我们的结果表明，ADT可能在克里斯琴森带的卷云的参数化和遥感中提供有用的近似值，其中折射率的实部接近于单位和/或相对吸收强。 （C）1998年美国眼镜学会。 [参考：36]

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