Abstract：

Disordered media, such as fog, powder, emulsion, and biological tissue, induce complex distortion of light, resulting in intricate speckle patterns. The memory effect, a key speckle correlation, reveals the translational invariance of the scattered field for thin-layer media. The memory effect aids in understanding, manipulating, and reconstructing the field, forming the basis of applications such as imaging through turbid materials, complex beam shaping, and surface characterization. However, neglecting decorrelation in the memory effect becomes a bottleneck in these applications, particularly in the multi-scattering regime. In this work, we report an "amnesia effect" in complex scattering systems, which provides an analytical formula for speckle decorrelation under general conditions. The amnesia effect predicts that the decorrelation of back-scattered light is a linear combination of decorrelations from thin-layer scattering and volumetric scattering. This model achieves state-of-the-art accuracy even for strong and multi-scattering cases, potentially providing an advanced forward model for various inverse problems. As a proof-of-concept, we present two examples, model-based particle size estimation and reconstruction of the incident beam profile, to validate this improvement. Our conclusions incorporate a wide range of systems—however thin-layer, multi-layer or bulk materials—and apply to all complex wave scattering problems.