Simulating light transmission and wavefront shaping in turbid media with a T-matrix method

Many optical techniques exploit interference in deterministic turbid media such as colloids and biological tissues. For instance, wavefront shaping methods that focus light in such materials do so by optimizing self-interference patterns. Despite significant interest, simulating such processes can be challenging. One issue is representing the known properties of the medium. Often, only mesoscale parameters such as the scattering coefficient are known. While these can be replicated—for example, using sphere suspensions designed via Mie theory—such representations are not directly compatible with simulation methods that require spatially sampled refractive index distributions. Another issue is computational complexity. Full-wave simulations traversing the length scales of practical experiments, e.g., thick biological tissue sections, are often beyond the limits of existing tools. To address this challenge, we developed a simulation method coupling together a sphere-based representation of the turbid media with a T-matrix method of computing the light fields. As T-matrix calculations can work directly on Mie-theory designed sphere suspensions, this provides a physically consistent and computationally efficient way to model coherent light transport in turbid media. To demonstrate the approach, we simulated light propagation and focusing in and around a diffusive layer and an 800 µm thick biological tissue section. By enabling deterministic coherent optics simulations in the ballistic, quasi-ballistic and diffusive regimes, the work provides a tool that could aid the development of a range of techniques exploiting coherent phenomena in turbid media.