Absorption effect on light scattering by dust particles in physical optics approximation

The paper investigates the scattering properties of cosmic dust particles using physical optics approximation, focusing on the identification of conditions under which the backscattered signal can be approximated by the specular component only. The analysis is given to the light scattering by irregular dust particles ranging in size from 5 to 100 μm, including pyroxene glass (n = 1.6847 + i0.0373) and graphite (n = 1.48 + i0.003). Geometrical parameters of the particles are measured for a statistically representative selection. It is found that for weakly absorbing materials like graphite, the backscattered signal becomes purely specular at the particle size exceeding 100 μm, whereas for strongly absorbing particles such as pyroxene glass, this occurs at 5 μm particles. Research findings are relevant for modeling stratospheric aerosol injection and interpreting lidar signals, where accurate optical models of cosmic dust are of great importance.