Impact of large-angle scattering on diffusively backscattered halos

Abstract

We discuss the impact of large-angle scattering events in highly forward-scattering media on the spatial distribution of the diffusively reflected light. We show that, even for highly forward-scattering media, the reflected light near the incident beam axis is strongly dependent on the small number of large-angle scattering events. Reliable modeling of near-axis reflection thus requires accurate knowledge of the scattering phase function's behavior at large angles.

Backscattering halo from the beam in the scattering medium with highly forward peaked phase function: is it feasible?

“…The asymptotic formula (2) has been derived using the radiative transfer equation (RTE) solution in the SAA with integration along the characteristics. This approximate solution does not account for the path length dispersion, and therefore the solution diverges at small phase angles and large optical thickness of the medium.…”

“…Direct Monte Carlo simulations [2] revealed the role of the backscattered radiation in possible manifestation of this effect in experiment. Namely, Campbell et al [2] concluded that the effect might be registered if the small part of the radiation scattered exactly backwards was somehow removed. Motivation of the present study is a theoretical assessment of practical feasibility of observation of this phenomenon in a realistic medium.…”

“…Several years ago, a phenomenon of the halo appearing in the backscattered radiation of the pencil beam source was theoretically revealed and discussed in papers [1,2]. However, direct experimental observations of the halo are still unknown.…”

“…That means that the backscattered radiation of the searchlight source near the beam axis and far from it are formed by the quasi singly backscattered and diffusively scattered radiation, respectively. Monte Carlo simulations [1,2] showed that if the CFSB contribution is suppressed, the diffuse part of radiation forms an annular halo around the searchlight beam axis, the radius of which is about one transport length of the radiation in the medium. What we plan to do is to compare analytical estimates of the backscattered field in the central and peripheral regions around the searchlight, and establish the conditions on a conservative medium that should be met in the experiment for an observation of the searchlight backscattering halo.…”

“…What we plan to do is to compare analytical estimates of the backscattered field in the central and peripheral regions around the searchlight, and establish the conditions on a conservative medium that should be met in the experiment for an observation of the searchlight backscattering halo. In contrast to previous studies that focused on the intensity profile in the momentum space [1][2][3], the present work studies the intensity profile in the real space.…”