Emergent scattering regimes in disordered metasurfaces near critical packing

Disordered metasurfaces provide a versatile platform for harnessing near- and far-field scattered light. Most research has focused on either particulate topologies composed of individual, well-identified metaatoms or, to a lesser extent, semi-continuous aggregate topologies without well identified inclusions. Here, we uncover an intermediate critical packing regime characterized by metasurface morphologies in which a significant fraction of metaatoms begin to connect. We experimentally demonstrate that, at this threshold, the properties of the scattered light abruptly change and, via a statistical quasinormal mode analysis, interpret this change as a marked transition in the statistics of the photon density of states. Unlike percolation in semicontinuous metal films, this transition affects not only the specular but also the diffuse components of the scattered light in a profound way. Our results introduce critical packing topologies as a novel design strategy for manipulating the spectral and angular characteristics of light using ultrathin optical coatings. Emergent functionalities include colour shifts in diffuse light driven by multiple scattering and surface whitening, with potential applications in display technologies, for example, to reduce glare in electronic screens.

💡 Research Summary

This paper presents a groundbreaking discovery in the field of nanophotonics, identifying a previously overlooked optical regime known as “critical packing” within disordered metasurfaces. Traditionally, research into metasurfaces has been bifurcated into two distinct domains: particulate topologies, consisting of well-defined, isolated metaatoms, and semi-continuous aggregate topologies, where the boundaries between inclusions are indistinct. This study bridges this gap by investigating the intermediate regime where metaatoms begin to physically interconnect, uncovering emergent scattering phenomena that occur at this structural threshold.

The researchers experimentally demonstrated that at the critical packing threshold, the scattering properties of light undergo an abrupt and profound transition. To understand the underlying physics, the team employed a statistical quasinormal mode (QNM) analysis, which revealed that this transition is driven by a significant shift in the statistics of the photon density of states (PDOS). This is not merely a linear progression of structural change but a fundamental reconfiguration of how electromagnetic modes are distributed within the metasurface.

A key scientific distinction made in this work is the contrast between this phenomenon and the well-known percolation transition in continuous metal films. While standard percolation primarily affects the specular component of reflected light, the transition observed in the critical packing regime impacts both the specular and the diffuse components of scattered light. This implies that the onset of connectivity in disordered metaatoms triggers a complex redistribution of light through multiple scattering processes, fundamentally altering the angular and spectral characteristics of the surface.

The practical implications of this discovery are significant for the development of next-generation optical coatings. The ability to manipulate light through “critical packing topologies” allows for the engineering of emergent functionalities, such as controlled color shifts in diffuse light and “surface whitening” effects. These capabilities hold immense potential for display technologies, particularly in creating ultra-thin, anti-glare coatings for electronic screens that can reduce reflections without compromising visual clarity. By providing a new design strategy based on structural connectivity, this research opens a new frontier in the precision engineering of light-matter interactions in disordered nanostructures.