Free‐Electron Transparent Metasurfaces with Controllable Losses for Broadband Light Manipulation with Nanometer Resolution

Abstract

Controlling broadband light in nanoscale volumes is a desired goal in nanophotonics. Metastructures tackle this problem by subwavelength nanostructured patterns. The current technology reaches footprints of 50 nm with plasmonic nanostructures. Scaling down these values is challenging, especially in low loss dielectrics. Here, a new class of metasurfaces is introduced, “printed” point‐to‐point by free‐electron waves and created by altering the resonant atomic transition of inexpensive photosensitive materials. With this approach it is possible to directly write a desired distribution of refractive index and extinction coefficient with a resolution equal to the focusing accuracy of the electron beam, theoretically limited to the single nanometer. An application of this technology is illustrated in structural coloration. Currently, the best results are obtained with plasmonics at 127 000 dual polarization interferometry (DPI), with 50–200 nm structures and chromaticity ranging from blue to yellow. Free‐electron metasurfaces can generate the complete spectrum of colors of the cyan, yellow, magenta, and black system with resolutions up to 256 000 DPI, and nanostructures of 10 nm radius by using a single inexpensive layer of transparent material. This platform can enable a new generation of low cost transparent media supporting ultradense optical circuitry for broadband light control.

Disorder‐Induced Material‐Insensitive Optical Response in Plasmonic Nanostructures: Vibrant Structural Colors from Noble Metals

“…Here, we propose and realise a system achieving material insensitivity and strong light-matter interactions simultaneously. Given the versatile applications of disordered nanostructures [19,20,21,22,23,24,25,26,27,28,29], a disorder induced material-independent response may shed light on novel systems with a flexible material library. In this article, our investigation of the optical response is limited to the linear regime.…”

“…By virtue of random scattering, disordered structures are insensitive to optical parameters such as wavelength, incident angle and polarisation. [ 6,15–18 ] With judicious designs, disordered networks facilitated a repertoire of applications, including broadband reflector, [ 19 ] structural colors, [ 20–24 ] photocatalysis, [ 25 ] optical filters, [ 26 ] and lasers. [ 27–29 ] Here, we extend the insensitivity to the material's property in optics, demonstrating that disorder can effectively mitigate the material dependence of the optical response.…”

Reflective Coloration from Structural Plasmonic to Disordered Polarizonic

“…[128] In comparison to the plasmonic structural colors, and thanks to their superior reflectivity, the periodic dielectric nanostructures can produce much brighter and sharper structural colors. [129][130][131] Thus, it is expected to deal with a new class of reflective structural coloration systems based on lossless polarizonic dielectric pixels. Despite the mentioned merits of the dielectric nanostructures, the nature of polarizonic response in the disorder medium has been recognized with photoswitchable molecules, yet the negligible refractive index contrast still could be challenging.…”

Broadband vectorial ultrathin optics with experimental efficiency up to 99% in the visible region via universal approximators

“…Flat optics aims to address this problem by replacing conventional optics with highly integrated nanostructured surfaces. This technology has attracted enormous interest, with a large variety of designs demonstrated such as lenses 2,[4][5][6][7] , holograms [8][9][10][11][12] , filters [13][14][15] and other components capable of outperforming their traditional counterparts 16-23 . In the visible range, the use of dielectric nanostructures for the production of these devices has gained favour, as metallic designs suffer from significant ohmic losses, particularly when transmissive elements are desired 24 . Currently, the challenges being addressed at visible frequencies are related to the scalability of the structure fabrication, the design of different types of broadband functionalities, and the increase of the operational and transmission efficiency, which is essential to enable complex layer-by-layer integration [25][26][27] .…”