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Random lasers are resonator-less light sources where feedback stems from recurrent scattering at the expense of spatial profile and directionality. Suitably-doped nematic liquid crystals can random lase when optically pumped near resonance(s); moreover, through molecular reorientation within the transparency region, they support self-guided optical spatial solitons, i.e., light-induced waveguides. Here, we synergistically combine solitons and collinear pumping in weakly scattering dye-doped nematic liquid crystals, whereby random lasing and self-confinement concur to beaming the emission, with several improved features: all-optical switching driven by a low-power input, laser directionality and smooth output profile with high-conversion efficiency, externally controlled angular steering. Such effects make soliton-assisted random lasers an outstanding route towards application-oriented random lasers. Owing to their lack of a conventional cavity, random lasers typically do not emit a defined beam in a specific direction. Here, the authors combine spatial solitons and collinear pumping to achieve light-confined random lasing with a smooth output profile and a controllable direction of emission.

Optical coatings are integral components of virtually every optical instrument. However, despite being a century-old technology, there are only a handful of optical coating types. Here, we introduce a type of optical coatings that exhibit photonic Fano resonance, or a Fano-resonant optical coating (FROC). We expand the coupled mechanical oscillator description of Fano resonance to thin-film nanocavities. Using FROCs with thicknesses in the order of 300 nm, we experimentally obtained narrowband reflection akin to low-index-contrast dielectric Bragg mirrors and achieved control over the reflection iridescence. We observed that semi-transparent FROCs can transmit and reflect the same colour as a beam splitter filter, a property that cannot be realized through conventional optical coatings. Finally, FROCs can spectrally and spatially separate the thermal and photovoltaic bands of the solar spectrum, presenting a possible solution to the dispatchability problem in photovoltaics, that is, the inability to dispatch solar energy on demand. Our solar thermal device exhibited power generation of up to 50% and low photovoltaic cell temperatures (~30 °C), which could lead to a six-fold increase in the photovoltaic cell lifetime. A thin-film optical coating exhibits Fano resonance showing promising applications in structural colouring of transparent objects and hybrid thermal and photovoltaic power generation.

Structural coloring is a photostable and environmentally friendly coloring approach that harnesses optical interference and nanophotonic resonances to obtain colors with a range of applications including display technologies, colorful solar panels, steganography, décor, data storage, and anticounterfeiting measures. We show that optical coatings exhibiting the photonic Fano Resonance present an ideal platform for structural coloring; they provide full color access, high color purity, high brightness, controlled iridescence, and scalable manufacturing. We show that an additional oxide film deposited on Fano resonant optical coatings (FROCs) increases the color purity (up to 99%) and color gamut coverage range of FROCs to 61% of the CIE color space. For wide-area structural coloring applications, FROCs have a significant advantage over existing structural coloring schemes. Fano resonant optical coatings (FROCs) present an ideal platform for structural coloring from thin-film metamaterials. This platform provides full-color gamut coverage at greater than 61% of the CIE gamut, with exceptionally high purity (up to 99%) and high brightness. FROCs exhibit tunable iridescence, cost-effective and scalable manufacturing, and significant advantages over existing structural coloring schemes.

Augmented and virtual reality (AR/VR) is transforming how humans interact with technology in a wide range of fields and industries, from healthcare and education to entertainment. However, current device limitations have impeded wider integration. Tunable holographic metasurfaces represent a promising platform for revolutionizing AR/VR devices by precisely controlling light at the subwavelength scale. This article examines current challenges and opportunities from both the AR/VR and holographic metamaterial perspectives and explores how improvements to state-of-the-art approaches can address these challenges. In particular, we propose a focus on easily manufacturable and broadly electrically tunable metasurface technologies including liquid crystal integration and excitonic tuning in 2D materials. Advanced metasurface optimization techniques including machine learning will also be crucial for exploring the large design space.

In recent years, considerable research efforts have been focused on near-perfect and perfect light absorption using metamaterials spanning frequency ranges from microwaves to visible frequencies. This relatively young field is currently facing many challenges that hampers its possible practical applications. In this paper, we present grating coupled-hyperbolic metamaterials (GC-HMM) as multiband perfect absorber that can offer extremely high flexibility in engineering the properties of electromagnetic absorption. The fabricated GC-HMMs exhibit several highly desirable features for technological applications such as polarization independence, wide angle range, broad- and narrow- band modes, multiband perfect and near perfect absorption in the visible to near-IR and mid-IR spectral range. In addition, we report a direct application of the presented system as an absorption based plasmonic sensor with a record figure of merit for this class of sensors.

Doped semiconductors can exhibit metallic-like properties ranging from superconductivity to tunable localized surface plasmon resonances. Diamond is a wide-bandgap semiconductor that is rendered electronically active by incorporating a hole dopant, boron. While the effects of boron doping on the electronic band structure of diamond are well-studied, any link between charge carriers and plasmons has never been shown. Here, we report intervalence plasmons in boron-doped diamond, defined as collective electronic excitations between the valence subbands, opened up by the presence of holes. Evidence for these low-energy excitations is provided by valence electron energy loss spectroscopy and near-field infrared spectroscopy. The measured spectra are subsequently reproduced by first-principles calculations based on the contribution of intervalence band transitions to the dielectric function. Our calculations also reveal that the real part of the dielectric function exhibits a crossover characteristic of metallicity. These results suggest a new mechanism for inducing plasmon-like behavior in doped semiconductors, and the possibility of attaining such properties in diamond, a key emerging material for quantum information technologies. Doping diamond with boron is well known to change its electronic structure. Here, the authors reveal low-energy collective excitations in boron-doped diamond, which originate from intervalence band transitions.

Sensitivity and specificity in biosensing platforms remain key aspects to enable an effective technological transfer. Considerable efforts have been made to design sensing platforms capable of controlling light–matter interaction at the nanoscale. Here, we numerically investigated how a 3D out-of-plane chiral plasmonic metasurface can be used as a key element in a sensing platform, by exploiting the variation in the plasmonic and lattice modes as a function of the refractive index of the surrounding medium. The results indicate that chiral metasurfaces can be used to perform sensing, by detecting the refractive index change with a maximum sensitivity of 761 nm/RIU. The metasurface properties can be suitably designed to maximize the optical response in terms of the shift, modulated by the refractive index of the analyte molecules. Such studies can pave the way for engineering and fabricating highly selective and specific chiral metasurface-based refractive index sensing platforms.

A MIMI (metal–insulator-metal–insulator) nanoparticle was conceived and synthesized. It consists of a core of gold nanoparticles of different shapes, covered by a silica shell in turn covered by a layer of gold and finally by another silica shell. This hybrid nano-matryoshka, completely dispersed in water, was characterized by UV–Vis and TEM spectroscopy, comparing the architecture and photophysical properties of each synthetic step. Through a numerical simulation, it was possible to study in depth the absorption and extinction cross sections, determining the role of the various layers. This is an example of architecture used in the construction of metamaterials, the first in the form of a water-dispersed nanoparticles.