Depth-Targeted Energy Deposition Deep Inside Scattering Media

TL;DR

This paper introduces the 'deposition matrix' to predict and experimentally demonstrate the maximum energy deposition inside diffusive media, revealing fundamental limits and mechanisms for deep wave focusing.

Contribution

It presents a theoretical framework and experimental validation for optimizing energy delivery deep inside scattering media using the deposition matrix and eigenstate excitation.

Findings

Maximum energy enhancement occurs at 3/4 of the medium's thickness.

Deposition matrix eigenstates enable targeted energy control.

Enhancement results from eigenchannel excitation and interference effects.

Abstract

A grand challenge in fundamental physics and practical applications is overcoming wave diffusion to deposit energy into a target region deep inside a diffusive system. While it is known that coherently controlling the incident wavefront allows diffraction-limited focusing inside a diffusive system, in many applications targets are significantly larger than such a focus and the maximum deliverable energy remains unknown. Here, we introduce the "deposition matrix", which maps an input wavefront to its internal field distribution, and theoretically predict the ultimate limitations on energy deposition at any depth. For example, the maximum obtainable energy enhancement occurs at 3/4 a diffusive system's thickness: regardless of its scattering strength. Experimentally we measure the deposition matrix and excite its eigenstates to enhance/suppress the energy within an extended target region. Our theoretical analysis reveals that such enhancement/suppression results from both selective transmission eigenchannel excitation and constructive/destructive interference among these channels.