Time domain analysis of photon scattering and Huygens-Fresnel back projection

Stand-off detection and characterization of scattering media such as fog and aerosols is an important task in environmental monitoring and related applications. We present, for the first time, a stand-off characterization of sprayed water tog in the time domain. Using a time correlated single photon counting, we measure transient signatures of photons reflected off a target within the fog volume. We can distinguish ballistic from scattered photon. By application of a forward propagation model, we reconstruct the scattered photon paths and determine the fog's mean scattering length mu(scat.) in a range of 1.55 m to 1.86m. Moreover, in a second analysis, we project the recorded transients back to reconstruct the scene using virtual Huygens-Fresnel wavefronts. While in medium-density fog some contribution of ballistic remain in the signatures, we could demonstrate that in high-density fog, all recorded photons are at least scattered a single time. This work may path the way to novel characterization tools of and enhanced imaging in scattering media. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement