Probing the Position Resolved Energy Density Inside Photonic Scattering Slabs with Strong Absorption and Anisotropy

Understanding the transport of light in photonic scattering media is crucial for many application areas, such as atmospheric and climate sciences [1,2], oceanography [3], biophysics [4,5], powder technology [6], and solid-state lighting [7,8]. In photonic scattering media, such as paint, foam, and tissue, the refractive index varies spatially causing incident waves to be scattered and absorbed [9,10]. While Monte Carlo simulations accurately describe light transport in complex media, they are extremely slow and require high computation power. Fast and accurate analytical methods are needed especially for industrial applications. The P1 approximation to the radiative transfer equation (RTE) is a commonly utilized analytical method [11]. However, it is known that P1 fails for samples with both predominant forward scattering and strong absorption, resulting in unphysical negative energy densities. The accuracy of the analytical PN approximation depends on the order N, the scattering properties of the sample, like albedo, anisotropy, optical thickness, and refractive index contrast of the sample and the surrounding medium [12].