Light scattering from spherical and irregular particles over a wide angular range

We present laboratory measurements of angular light scattering intensity for aerosolized, micron-sized, irregularly shaped aluminum oxide (Al2O3) abrasive powders with different grit sizes. The measurements were carried out with the scattering angle ranging from 0.32 degrees to 177.6 degrees. First, we demonstrate that the light scattering inferred diameters were in good agreement with the intensity-weighted mean sizes and discuss the importance of intensity-weighted size distributions. Second, the wide range of scattering angles motivated us to visualize the same scattering intensity data with three methods: (a) logarithmically versus linear scattering angle theta, (b) logarithmically versus the logarithmic magnitude of the scattering wave vector q for forward scattering, the method of Q - space analysis, and (c) logarithmically (last approximate to 20 degrees of theta) versus linear phase angle (180 degrees - theta). The combination of these viewpoints yields a comprehensive description of the scattering that corresponds to dividing angular scattering into three regimes: forward-, side-, and back - scattering. The light scattering measurements were compared to the Mie scattering calculated for homogenous, spherical particles with the same volume-equivalent size distribution as that of the Al2O3 particles determined with an aerodynamic particle sizer. Experimental and Mie-theory results were well-matched in the forward regime which is clearly shown in Q - space but showed a poor matching in the side and backscattering regimes, as displayed in theta- and (180 degrees- theta) space, respectively.