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Nanoporous metals are a class of nanostructured materials finding extensive applications in multiple fields thanks to their unique properties attributed to their high surface area and interconnected nanoscale ligaments. They can be prepared following different strategies, but the deposition of an arbitrary pure porous metal is still challenging. Recently, a dry synthesis of nanoporous films based on the plasma treatment of metal thin layers deposited by physical vapour deposition has been demonstrated, as a general route to form pure nanoporous films from a large set of metals. An interesting aspect related to this approach is the possibility to apply the same methodology to deposit the porous films as a multilayer. In this way, it is possible to explore the properties of different porous metals in close contact. As demonstrated in this paper, interesting plasmonic properties emerge in a nanoporous Au–Ag bi-layer. The versatility of the method coupled with the possibility to include many different metals, provides an opportunity to tailor their optical resonances and to exploit the chemical and mechanical properties of components, which is of great interest to applications ranging from sensing, to photochemistry and photocatalysis.

Novel optical sources require fast decay rates, making hyperbolic metamaterials (HMMs) an increasingly attractive option. HMMs are well‐known for their remarkable anisotropy, and leverage hyperbolic dispersion to enhance the decay rate of a fluorophore placed on top of them. This study tackles the complex task of embedding a fluorophore into an HMM, successfully overcoming challenges related to surface roughness, thickness imperfections, and layer washing effects. Specifically, CsPbBr3 perovskite nanocrystals (NCs)‐based HMM are fabricated, by alternating silver/nanocrystals (Ag/NCs) layers. Through a systematic investigation of the photophysical response following the deposition of each bilayer, compelling evidence of the achievement of hyperbolic dispersion is provided. Specifically, the impact of "high‐k" modes is isolated, which is distinctive to the HMM architecture. Therefore, the longstanding debate regarding the number of bilayers needed to achieve hyperbolic dispersion is conclusively resolved. The research demonstrates a nearly twofold increase in the decay rate and a threefold enhancement in photoluminescence intensity. These findings are further supported by theoretical Purcell factor calculations. This study marks a pioneering advancement in the field of bulk dye‐embedded HMMs, laying the groundwork for the development of advanced optical sources such as "resonant gain HMMs". [ABSTRACT FROM AUTHOR]

Raman spectroscopy plays a pivotal role in spectroscopic investigations. The small Raman scattering cross-section of numerous analytes, however, requires enhancement of the signal through specific structuring of the electromagnetic and morphological properties of the underlying surface. This enhancement technique is known as surface-enhanced Raman spectroscopy (SERS). Despite the existence of various proposed alternatives, the approach involving Fabry–Pérot cavities, which constitutes a straightforward method to enhance the electromagnetic field around the analyte, has not been extensively utilized. This is because, for the analyte to experience the maximum electric field, it needs to be embedded within the cavity. Consequently, the top mirror of the cavity will eventually shield it from the external laser source. Recently, an open-cavity configuration has been demonstrated to exhibit properties similar to the classic Fabry–Pérot configuration, with the added advantage of maintaining direct accessibility for the laser source. This paper showcases how such a simple yet innovative configuration can be effectively utilized to achieve remarkable Raman enhancement. The simple structure, coupled with its inexpensive nature and versatility in material selection and scalability, makes it an ideal choice for various analytes and integration into diverse Raman apparatus setups. [ABSTRACT FROM AUTHOR]

Bio‐inspired and biodegradable quantum optics scenarios constitute a pathway toward environmentally friendly front‐end technologies. Such an inspiring perspective necessitates the replacement of classic gain materials with a biological counterpart like photoluminescent bacteria. It is easy to imagine that, in this case, a planar and cell‐viable substitute of classic bulk solid‐states resonators can be highly beneficial. In this paper a micro‐ and nano‐photonic structuration of both a standard and a functionalized version of a typical bacterial growth medium (Luria‐Bertani Agar – LBA) is successfully realized. Three structures belonging to the categories of photonic crystals are replicated, such as quasi‐crystals and meta‐surfaces, demonstrating how the proposed media can be used as templates for high‐end photonic applications. The optical quality of the replicated structures is confirmed by far‐field diffraction measurements. The structured growth media allow for a broad control of the surface wettability by accessing a so‐called Wenzel state, in which the original hydrophilicity of a material is increased due to the photonic structuration. Finally, the suitability of the nano‐structured LBA as a plasmonic platform is evidenced. The proposed micro‐and nano‐structured photonic growth media constitute the first, fundamental step toward quantum optical frameworks from biological media. [ABSTRACT FROM AUTHOR]

Ferrell and Berreman modes are absorption resonances in thin metal films and polar-dielectric media that arise from radiative bulk plasmon-polariton and phonon-polariton excitations. Compared to surface polaritons, Ferrell and Berreman modes occur due to volume charge oscillations across the medium and provide a unique pathway for light–matter interactions. Though the resonances are studied individually, stringent polarization and material requirements have prevented their observation in one host medium. Here, we show simultaneous excitation of Ferrell and Berreman absorption resonances in refractory epitaxial TiN/Al0.72Sc0.28N plasmonic metal/polar-dielectric hyperbolic metamaterials in the visible and far-infrared spectral ranges. The nanoscale periodicity of the superlattices enables the coupling of bulk plasmons (and longitudinal optical phonons) across different TiN (and Al0.72Sc0.28N) layers and allows polarization matching with free-space light that results in Ferrell (and Berreman) mode excitations. Ferrell and Berreman absorption resonances can be used for strong light confinement in radiative cooling, thermophotovoltaics, and other dual-band applications. [ABSTRACT FROM AUTHOR]