We demonstrate how tuneable Distributed Bragg Reflectors (DBRs) and resonant micro-cavities can be built by a scalable layer assembly of the transparent utility rubbers polydimethylsiloxane and polystyrene-polyisoprene. Stretching the devices by more than 60% leads to an affine contraction of the layer thicknesses thereby tuning both DBR and cavity modes across the entire visible spectrum. Such rapidly- and reversibly- stretch-tuneable cavities can be used in tuneable micro-lasers and for quantitative optical strain sensing applications.
Much interest has been shown recently in metallodielectric multilayer structures due to their potential for near-field imaging and lithography applications in the visible region of the spectrum. It was originally proposed that a single silver layer could be used as a flat lens for a single polarization [1] focusing incident light to an image by negative refraction. Additionally, such a lens was predicted to support the evanescent modes of an image, thus bypassing the resolution limit experienced by conventional lenses. The normally evanescent sub-wavelength details of an image are able to couple with the surface plasmons that reside upon the metal layer and are sustained resonantly through the slab. This has huge implications in near-field microscopy, where it could be used to uncover details that are not possible to resolve with conventional lenses. However, in practice, this simple system has serious limitations due to the large absorption of metals in the visible region, where the skin depth of gold and silver is around 10 nm. Consequently, an improved performance was suggested based on a periodic stack of metal and dielectric layers.[2] Since the evanescent components of an image undergo periodic amplification and decay at each interface within the multilayer, the field intensity is prevented from becoming too high at any point within the medium, and hence the resolution is improved. As the thickness, t, of these layers decreases (t ( l), the effective medium approximation becomes valid and the metamaterial can then be described by the macroscopic optical parameters, e and m. However, effective fabrication of appropriate structures is currently the focus of active research.Traditionally, such multilayers required vacuum deposition and utilized only small areas, limiting their potential application. Although two-source sputtering has been used to effectively fabricate bimetallic X-ray mirrors with up to 100 layers, [3] this process requires significant time and cost. Two-source sputtering has also been used to fabricate Ag/MgF 2 superlenses consisting of 16 curved layers; [4] however, these structures are inherently brittle, and their fabrication is hard to control, slow, and expensive. Metal-semiconductor multilayers have also been constructed, where a lattice-mismatched semiconductor bilayer leads to induced roll-up. [5,6] Unfortunately, this approach has severe limitations in the choice of layer thicknesses and of materials (which have to be grown by molecular beam epitaxy in specific alloy combinations). With layers thicker than 20 nm, strain relaxation occurs, leading to misfit dislocations that tear the top semiconductor layer apart. It would thus be very desirable to fabricate similar structures from flexible materials such as polymers, extending their potential applicability greatly and allowing scale-up of metamaterials fabrication for the first time.Here, we demonstrate a new and significantly more adaptable approach to the fabrication of multilayer metamaterials by growing a single metal-polymer bil...
A direct-assembly method to construct three-dimensional (3D) plasmonic nanostructures yields porous plasmonic rolls through the strain-induced self-rolling up of two-dimensional metallic nanopore films. This route is scalable to different hole sizes and film thicknesses, and applicable to a variety of materials, providing general routes towards a diverse family of 3D metamaterials with nano-engineerable optical properties. These plasmonic rolls can be dynamically driven by light irradiation, rolling or unrolling with increasing or decreasing light intensity. Such dynamically controllable 3D plasmonic nanostructures offer opportunities both for sensing and feedback in active nano-actuators.
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