Steam generation using solar energy provides the basis for many sustainable desalination, sanitization, and process heating technologies. Recently, interest has arisen for low-cost floating structures that absorb solar radiation and transfer energy to water via thermal conduction, driving evaporation. However, contact between water and the structure leads to fouling and pins the vapour temperature near the boiling point. Here we demonstrate solar-driven evaporation using a structure not in contact with water. The structure absorbs solar radiation and re-radiates infrared photons, which are directly absorbed by the water within a sub-100 μm penetration depth. Due to the physical separation from the water, fouling is entirely avoided. Due to the thermal separation, the structure is no longer pinned at the boiling point, and is used to superheat the generated steam. We generate steam with temperatures up to 133 °C, demonstrating superheated steam in a non-pressurized system under one sun illumination.

Unlike conventional optics, plasmonics enables unrivalled concentration of optical energy well beyond the diffraction limit of light. However, a significant part of this energy is dissipated as heat. Plasmonic losses present a major hurdle in the development of plasmonic devices and circuits that can compete with other mature technologies. Until recently, they have largely kept the use of plasmonics to a few niche areas where loss is not a key factor, such as surface enhanced Raman scattering and biochemical sensing. Here, we discuss the origin of plasmonic losses and various approaches to either minimize or mitigate them based on understanding of fundamental processes underlying surface plasmon modes excitation and decay. Along with the ongoing effort to find and synthesize better plasmonic materials, optical designs that modify the optical powerflow through plasmonic nanostructures can help in reducing both radiative damping and dissipative losses of surface plasmons. Another strategy relies on the development of hybrid photonicplasmonic devices by coupling plasmonic nanostructures to resonant optical elements. Hybrid integration not only helps to reduce dissipative losses and radiative damping of surface plasmons, but also makes possible passive radiative cooling of nano-devices. Finally, we review emerging applications of thermoplasmonics that leverage Ohmic losses to achieve new enhanced functionalities. The most successful commercialized example of a loss-enabled novel application of plasmonics is heat-assisted magnetic recording. Other promising technological directions include thermal emission manipulation, cancer therapy, nanofabrication, nano-manipulation, plasmon-enabled material spectroscopy and thermo-catalysis, and solar water treatment. OCIS codes: (240.6680) Surface plasmons; (230.3990) Micro-optical devices; (130.6010) Sensors; (350.5340) Photothermal effects; (290.6815) Thermal emission; (240.6675) Surface photoemission and photoelectron spectroscopy; (350.6670) Surface photochemistry.

Abstract:We developed planar multilayered photonic-plasmonic structures, which support topologically protected optical states on the interface between metal and dielectric materials, known as optical Tamm states. Coupling of incident light to the Tamm states can result in perfect absorption within one of several narrow frequency bands, which is accompanied by a singular behavior of the phase of electromagnetic field. In the case of near-perfect absorptance, very fast local variation of the phase can still be engineered. In this work, we theoretically and experimentally demonstrate how these drastic phase changes can improve sensitivity of optical sensors. A planar Tamm absorber was fabricated and used to demonstrate remote near-singular-phase temperature sensing with an over an order of magnitude improvement in sensor sensitivity and over two orders of magnitude improvement in the figure of merit over the standard approach of measuring shifts of resonant features in the reflectance spectra of the same absorber. Our experimentally demonstrated phase-to-amplitude detection sensitivity improvement nearly doubles that of state-of-the-art nano-patterned plasmonic singular-phase detectors, with further improvements possible via more precise fabrication. Tamm perfect absorbers form the basis for robust planar sensing platforms with tunable spectral characteristics, which do not rely on low-throughput nano-patterning techniques.Keywords: Tamm plasmons, surface modes, photonic crystals, optical impedance, geometrical phase, singular phase detection, bio(chemical) and temperature sensing Optical transduction is a widely used detection mechanism in remote sensing and monitoring of a variety of physical, chemical, and biological events. It is based on measuring environmental changes by detecting the change in one of the characteristics of light interacting with the target medium, including its amplitude, wavelength, incident angle, and phase. Optical sensing is intrinsically non-invasive, and can be used in extreme conditions, such as high toxicity, high temperatures, electrical noises, or strong magnetic fields. Among many types of optical sensors, surface-plasmon polariton (SPP) sensors are widely investigated and used [1][2][3][4][5][6][7] . Evanescent fields of SPP modes supported by metallic structures strongly interact with the surrounding dielectric medium, and environmentally-induced changes of their propagation constants provide an optical transduction mechanism 4 . Excitation of localized SPP modes generates strong electromagnetic field in a small volume close to the metal-dielectric interface, making possible detection of very small variations of the local refractive index. Hence, the SPP sensors offer highly-sensitive, label-free, and non-destructive optical detection and monitoring of chemical and 2 biological reactions on the surface. A common scheme of the SPP excitation on planar interfaces is the Kretschmann−Raether scheme, where a prism is placed on top of the metal film to excite surface plasmon polarito...

The equality between the spectral, directional emittance and absorptance of an object under local thermal equilibrium is known as Kirchhoff's law of radiation. The breakdown of Kirchhoff's law of radiation is physically allowed by breaking time-reversal symmetry and can open new opportunities for novel non-reciprocal light emitters and absorbers. Large anomalous Hall conductivity and angle recently observed in topological Weyl semimetals, particularly type-I magnetic Weyl semimetals and type-II Weyl semimetals, are expected to create large nonreciprocal electromagnetic wave propagation. In this work, we focus on type-I magnetic Weyl semimetals and show via modeling and simulation that non-reciprocal surface plasmons polaritons can result in pronounced non-reciprocity without an external magnetic field. The modeling in this work begins with a single pair of Weyl nodes, followed by a more realistic model with multiple paired Weyl nodes. Fermi-arc surface states are also taken into account through the surface conductivity. This work points to the promising applicability of topological Weyl semimetals for magneto-optical and energy applications. . These authors contributed equally to this work. Main textKirchhoff's law of radiation establishes the equality between the spectral, directional absorptance ( , ) and the spectral, directional emittance ( , ) of an object in local thermal equilibrium, i.e., ( , ) = ( , ) , where and are the wavelength and the direction of incoming and outgoing radiation, respectively. Fundamentally, Kirchhoff's law of radiation underlies the theoretical efficiency limit in radiative energy conversion since converting absorbed incoming radiation into another form of energy, such as electricity or heat, always entails the outgoing emission at the same wavelength in the same direction from the object, which causes an intrinsic loss 1-3 . It has been argued 2,4,5 that Kirchhoff's law of radiation is not a required condition for the validity of the second law of thermodynamics in systems that exchange radiative energy, but rather a result of the Lorentz reciprocity theorem in which the only assumptions are a linear constitutive relation and symmetric permittivity and permeability tensors 6,7 . Thus, the violation of Kirchhoff's law of radiation, i.e., non-reciprocity in the spectral, directional absorptance and emittance, is physically allowed, and its realization can open new opportunities for novel light emitters and absorbers for a wide range of radiative applications including solar photovoltaics, thermo-photovoltaics, and antennas 1,8 .Non-reciprocity in a medium often arises due to non-zero anti-symmetric off-diagonal elements of the dielectric tensor of the medium, which creates non-reciprocal electromagnetic modes 9 . One way to create the anti-symmetric off-diagonal elements is by inducing magnetic responses either by the Hall response under an external magnetic field or by spontaneous magnetization in materials, namely the anomalous Hall effect 10 . The anomalous Hall effect can origin...

Structural colors are a result of the scattering of certain frequencies of the incident light on micro-or nano-scale features in a material. This is a quite different phenomenon to that of colors produced by absorption of different frequencies of the visible spectrum by pigments or dyes, which is the most common way of coloring used in our daily life. However, structural colors are more robust and can be engineered to span most of the visible spectrum without changing the base material, only its internal structure. They are abundant in nature, with examples as colorful as beetles covers and butterfly wings, but there are few ways of preparing them for large-scale commercial applications for real-world uses. In this work, we present a technique to create a full gamut of structural colors based on a low-cost, robust and scalable fabrication of periodic network structures in porous alumina as well as the strategy to theoretically predict and engineer different colors on demand. We experimentally demonstrate mesoporous network metamaterial structures with engineered colors spanning the whole optical spectrum and discuss their applications in sensing, environmental monitoring, biomimetic tissues engineering, etc.