Dependent scattering and absorption by densely packed discrete spherical particles: Effects of complex refractive index

- Muller matrix of densely packed spheres with different complex refractive indexes is investigated.
- Influence of particle complex refractive index on dependent scattering and absorption is discussed.
- Stronger dependent effects were observed for medium size particles with higher refractive index contrasts with the host medium.
- Highly absorbing particles show both prominent dependent scattering and absorption effects.
- Dependent scattering correction by hard sphere model deteriorates at large phase shift parameters.

Due to the dependent scattering and absorption effects, the radiative transfer equation (RTE) may not be suitable for dealing with radiative transfer in dense discrete random media. This paper continues previous research on multiple and dependent scattering in densely packed discrete particle systems, and puts emphasis on the effects of particle complex refractive index. The Mueller matrix elements of the scattering system with different complex refractive indexes are obtained by both electromagnetic method and radiative transfer method. The Maxwell equations are directly solved based on the superposition T-matrix method, while the RTE is solved by the Monte Carlo method combined with the hard sphere model in the Percus-Yevick approximation (HSPYA) to consider the dependent scattering effects. The results show that for densely packed discrete random media composed of medium size parameter particles (equals 6.964 in this study), the demarcation line between independent and dependent scattering has remarkable connections with the particle complex refractive index. With the particle volume fraction increase to a certain value, densely packed discrete particles with higher refractive index contrasts between the particles and host medium and higher particle absorption indexes are more likely to show stronger dependent characteristics. Due to the failure of the extended Rayleigh-Debye scattering condition, the HSPYA has weak effect on the dependent scattering correction at large phase shift parameters.