Diffusive-light invisibility cloak for transient illumination

Abstract

Invisibility in a diffusive-light-scattering medium has been recently demonstrated by employing a scatteringcancellation core-shell cloak. Unlike nondiffusive cloaks, such a device can be simultaneously macroscopic, broadband, passive, polarization independent, and omnidirectional. Unfortunately, it has been verified that this cloak, as well as more sophisticated ones based on transformation optics, fail under pulsed illumination, invalidating their use for a variety of applications. Here, we introduce a different approach based on unimodular transformations that enables the construction of unidirectional diffusive-light cloaks exhibiting a perfect invisibility effect, even under transient conditions. Moreover, we demonstrate that a polygonal cloak can extend this functionality to multiple directions with a nearly ideal behavior, while preserving all other features. We propose and numerically verify a simple cloak realization based on a layered stack of two isotropic materials. The studied devices have several applications not addressable by any of the other cloaks proposed to date, including shielding from pulse-based detection techniques, cloaking undesired scattering elements in time-of-flight imaging or high-speed communication systems for diffusive environments, and building extreme optical security features. The discussed cloaking strategy could also be applied to simplify the implementation of thermal cloaks.

Imaging cloaked objects: diffraction tomography of realistic invisibility devices

“…In particular, here we consider a hexagonal cloak [the details of which are shown in Fig. 2(c) as an example] and a square cloak, following the transformations reported in [24] and [25], respectively. In the case of the hexagonal cloak, the employed dimensions are r 2 = 4.8λ, r 1 = r 2 /3, and r 0 = 0.03λ.…”

Controlling Chemical Waves by Transforming Transient Mass Transfer

“…Unfortunately, transient mass transfer generally does not have the property of form‐invariance under coordinate transformations, so the existing transformation theory is not applicable. Although transient light transport and heat diffusion may provide some insights, [ 24–28 ] the related approaches are restricted to certain geometries or transformations. Therefore, the relevant theories are still confronted with big challenges to control chemical waves.…”

Broadband corner cloak using a uniaxial transformation medium of stacked artificial dielectric sheets

“…An isovolumetric transformation (so-called area-preserving or unimodular transformation) over one of the walls [27][28][29] has been introduced in the corner cloak. Since the transformation yields a spatially constant material parameters with unity permeability in contrast to general coordinate transformations including [26] with spatially variant parameters and nonunity permeability, the corner cloak can be implemented by a homogeneous nonmagnetic material, which can lower the technological hurdle in implementations.…”