Gold-core/palladium-shell metamaterials for hydrogen detection are presented. The more than 30% change in both the reflection and transmission from the metamaterial layer that is observed when the layer is exposed to 2% hydrogen mixture is clearly noticeable to the naked eye as a change in the brightness of light transmitted by the metamaterial. This sensor should make a contribution to the safety of processes involving hydrogen.
Slab photonic crystals (PhCs) are photonic structures used in many modern optical technologies. Fabrication of these components is costly and usually involves eco‐unfriendly methods, requiring modern nanofabrication techniques and cleanroom facilities. This work describes that diatom microalgae evolved elaborate and highly reproducible slab PhCs in the girdle, a part of their silicon dioxide exoskeletons. Under natural conditions in water, the girdle of the centric diatom Coscinodiscus granii shows a well‐defined optical pseudogap for modes in the near‐infrared (NIR). This pseudogap shows dispersion toward the visible spectral range when light is incident at larger angles, eventually facilitating in‐plane propagation for modes in the green spectral range. The optical features can be modulated with refractive index contrast. The unit cell period, a critical factor controlling the pseudogap, is highly preserved within individuals of a long‐term cultivated inbred line and between at least four different C. granii cell culture strains tested in this study. Other diatoms present similar unit cell morphologies with various periods. Diatoms thereby offer a wide range of PhC structures, reproducible and equipped with well‐defined properties, possibly covering the entire UV‐vis–NIR spectral range. Diatoms therefore offer an alternative as cost‐effective and environmentally friendly produced photonic materials.
Hyperbolic plasmonic metamaterials are important for designing sensing, nonlinear, and emission functionalities, which are, to a large extent, determined by the epsilon-near-zero behaviour observed close to an effective plasma frequency of the metamaterial. Here, we describe a method for tuning the effective plasma frequency of a gold nanorod-based metamaterial throughout the visible and near-infrared spectral ranges. These metamaterials, fabricated by two-step anodization in selenic acid and chemical post-processing, consist of nanorods with diameters of around 10 nm and interrod distances of around 100 nm and have a low effective plasma frequency down to a wavelength range below 1200 nm. Such metamaterials open up new possibilities for a variety of applications in the fields of bio- and chemical sensing, nonlinearity enhancement, and fluorescence control in the infrared.
We present an analytical description and an experimental realization of interscale mixing microscopy, a diffractionbased imaging technique that is capable of detecting wavelength/10 objects in far-field measurements with both coherent and incoherent broadband light. This method aims at recovering the spatial spectrum of light diffracted by a subwavelength object based on far-field measurements of the interference created by the object and a finite diffraction grating. A single measurement, analyzing the multiple diffraction orders, is often sufficient to determine the parameters of the object. The presented formalism opens the door for spectroscopy of nanoscale objects in the far-field.
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