Abstract In the present work, we propose a comparative study of optical properties in the visual spectral regime of porous dust particles having porosities ranging from 0% (compact particle) to 50% (as much matter as void in a same particle), generated using two different models considering particle as an ensemble of dipoles much smaller than wavelength. One of the models (the touching-dipoles model, named below: ‘‘TD model”) considers a homogeneous structure made up of touching dipoles (that is neighbouring); the dipoles are removed randomly one by one from a compact structure in such a way that the remaining structure is left connected. The other model (the non-touching-dipoles model, named below:’‘non-TD model”) generates porous particles by randomly removing dipoles without constraining the ensemble of dipoles to remain connected. The computations of the optical properties of these disordered particles are performed using Discrete Dipole Approximation (DDA) code. Linear polarization profiles and color (i.e. the ratio between the intensities of the light scattered by particles in the comet at 0.485 ​μm and 0.684 ​μm wavelengths expressed in log scale) curves are shown vs. the scattering angle, and compared for the two models at different porosities. The variation of scattering efficiency factor as a function of the size parameter (X) is also studied to point out sensitivity of light scattering to different pore structures (shape and size), comparing data from particles of same porosity but generated through different processes. The results are compared with Mie results where the effective refractive index for each porosity is calculated using Bruggemann mixing rule. It is observed that light scattering properties of the TD model is not much different from the EMT-Mie model, but the non-TD model differs significantly. These difference could be due to the fact that non-TD model contains a higher number of non-Rayleigh inclusions, as compared to the TD model.

中文翻译：

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具有连通或不连通偶极子的多孔尘埃粒子的光散射特性比较

摘要 在目前的工作中，我们建议对孔隙率从 0%（致密颗粒）到 50%（与同一颗粒中的空隙一样多）的多孔尘埃颗粒的可见光谱范围内的光学特性进行比较研究，使用两种不同的模型将粒子视为远小于波长的偶极子集合。其中一个模型（接触偶极子模型，命名如下：“TD模型”）考虑由接触偶极子（即相邻）组成的同质结构；偶极子从一个紧凑的结构中随机一个一个地移除，这样剩余的结构保持连接。另一个模型（非接触偶极子模型，命名如下：“非 TD 模型”）通过随机去除偶极子而不限制偶极子集合保持连接来生成多孔粒子。这些无序粒子的光学特性的计算是使用离散偶极近似 (DDA) 代码执行的。显示了线性偏振分布和颜色（即彗星中粒子在 0.485 μm 和 0.684 μm 波长处散射的光强度之间的比值，以对数刻度表示）与散射角的关系，并比较了两种模型在不同的孔隙率。还研究了散射效率因子作为尺寸参数 (X) 的函数的变化，以指出光散射对不同孔隙结构（形状和尺寸）的敏感性，比较来自相同孔隙率但通过不同过程产生的颗粒的数据。将结果与 Mie 结果进行比较，其中使用 Bruggemann 混合规则计算每个孔隙度的有效折射率。可以观察到，TD模型的光散射特性与EMT-Mie模型差别不大，但非TD模型差别很大。这些差异可能是由于与 TD 模型相比，非 TD 模型包含更多数量的非瑞利夹杂物。