Search

Chiral metasurfaces patterned with L-shaped holes in a thin film of Dirac semimetal Cd3As2 are designed. The impact of temperature T on circular conversion dichroism, mainly characterized by circular polarization differential transmittance (CPDT), is studied by rigorous coupled-wave analysis. The results show that decreasing T will give rise to the appearance of much more narrow CPDT peaks and dips, and the maximum differential transmittance between two opposite circularly polarized light can reach above 0.60 by optimizing the structural parameters at 80 K. As the T increases, the differential transmittance gradually decreases, and the CPDT peak and dip values exhibit variation tendencies of ‘Z’ and ‘S’ types, respectively. Two simple formulae of CPDT extreme values with respect to T are derived, predicting that the decreasing tendency will reach saturation when T ≥ 500 K. Differing from the wavelength-independent variation trend of differential transmittance, CPDT extremum positions mainly show a blueshift (redshift) tendency at the wavelength λ > 10 μm (λ < 5 μm) as the T increases. Moreover, evolutions of CPDT with various factors including the thickness of Cd3As2, incident and azimuth angles are also clearly unveiled.

We demonstrate SERS sensors utilizing gold nanoparticles formed on quartz substrates by rapid thermal annealing of extremely thin gold films. Our sensors achieved highly sensitive detection of self-assembled monolayer of BPT molecules.

We demonstrate mid-infrared SEIRA sensors employing an unconventional liquid-metal-based nanophotonic structure, which allows for convenient delivery of thin film analyte into the sensing hot spots. State-of-the-art SEIRA sensing performance was demonstrated for sensing monolayer 1-octadecanethiol.

Near-room-temperature liquid metals offer unique and crucial advantages over solid metals for a broad range of applications that require soft, stretchable, and/or reconfigurable structures and devices. In particular, gallium-based liquid metals are the most suitable for a wide range of applications, not only owing to their low melting points but also thanks to their low toxicity and negligible vapor pressure. In addition, gallium-based liquid metals exhibit attractive optical properties, which make them highly suitable for a variety of photonics applications. This review summarizes the material properties of gallium-based liquid metals, highlights several effective techniques for fabricating liquid-metal-based structures and devices, and then focuses on the various photonics applications of these liquid metals in different spectral regions, following with a discussion on the challenges and opportunities for future research in this relatively nascent field.

Surface-enhanced infrared absorption (SEIRA) spectroscopy can provide label-free, nondestructive detection and identification of analytes with high sensitivity and specificity, and therefore has been widely used for various sensing applications. SEIRA sensors usually employ resonant nanophotonic structures, which can substantially enhance the electric field and hence light-matter interactions by orders of magnitude in certain nanoscale hot spots of the devices. However, as ever, smaller hot spots are employed to further enhance the field, the delivery of analytes into such hot spots becomes increasingly challenging. Here, high-performance nanophotonic SEIRA sensors based on nanopatch antennas with a liquid gallium ground plane are demonstrated, which not only lead to ultrahigh field confinement and enhancement, but also allow for convenient and efficient delivery of analytes into nanometric hot spots by employing a simple procedure suitable for point-of-care applications. The sensors exhibit superior sensitivity in the midinfrared spectral region. Around 10% molecular vibrational signals (i.e., the modulation of a sensor's reflection spectrum owing to the molecular vibrational modes of the analytes) near 2900 cm

The photonic spin Hall effect (PSHE) is a promising candidate for controlling the spin states of photons and exploiting next-generation photonic devices based on spinoptics. Herein, the influences of a perpendicular magnetic field on the PSHE appearing on the surface of monolayer black phosphorus (BP) are investigated. Results reveal that both the in-plane and transverse spin-dependent shifts are quantised and show an oscillating pattern due to the splitting of Landau levels (LLs) induced by the external magnetic field B. And the oscillation period of spin Hall shifts gradually increases with strengthening B because of the increase of LL spacings. By contrast, for a fixed magnetic field, as the LL spacings become smaller and smaller with increasing the LL index, the oscillation period of spin Hall shifts gradually decreases as the photonic energy increases. Moreover, it is possibly due to the synergistic role of intrinsic anisotropy, high crystallinity, and quantisation-incurred localised decreases in beating-like complex conductivities of the BP film, giant spin Hall shifts, hundreds of times of the incident wavelength, are obtained in both transverse and in-plane directions. These unambiguously confirm the strong impact of the external magnetic field on the PSHE and shed important insights into understanding the rich magneto-optical transport properties in anisotropic two-dimensional atomic crystals.

Surface plasmons in graphene have great potential for molecular sensing applications thanks to their exceedingly high sensitivity to environmental changes. Here, we demonstrate a type of hybrid graphene–metal metasurface that supports strong graphene plasmonic resonances in the terahertz range. Each unit cell of such a hybrid metasurface consists of a graphene antidot enclosing a metal disk realized using a self-aligned photolithography process. This hybrid design combines the advantages of both graphene- and metal-based photonic structures, leading to ∼3 times stronger tunable plasmonic resonances and an order of magnitude larger near-field intensity enhancement with respect to those of bare graphene antidot metasurfaces.

Chiral metasurfaces patterned with L-shaped holes in a thin film of Dirac semimetal Cd3As2 are designed. The impact of temperature T on circular conversion dichroism, mainly characterized by circular polarization differential transmittance (CPDT), is studied by rigorous coupled-wave analysis. The results show that decreasing T will give rise to the appearance of much more narrow CPDT peaks and dips, and the maximum differential transmittance between two opposite circularly polarized light can reach above 0.60 by optimizing the structural parameters at 80 K. As the T increases, the differential transmittance gradually decreases, and the CPDT peak and dip values exhibit variation tendencies of 'Z' and 'S' types, respectively. Two simple formulae of CPDT extreme values with respect to T are derived, predicting that the decreasing tendency will reach saturation when T ≥ 500 K. Differing from the wavelength-independent variation trend of differential transmittance, CPDT extremum positions mainly show a blueshift (redshift) tendency at the wavelength λ10 μm (λ5 μm) as the T increases. Moreover, evolutions of CPDT with various factors including the thickness of Cd3As2, incident and azimuth angles are also clearly unveiled.

Nanophotonic resonators can confine light to deep-subwavelength volumes with highly enhanced near-field intensity and therefore are widely used for surface-enhanced infrared absorption spectroscopy in various molecular sensing applications. The enhanced signal is mainly contributed by molecules in photonic hot spots, which are regions of a nanophotonic structure with high-field intensity. Therefore, delivery of the majority of, if not all, analyte molecules to hot spots is crucial for fully utilizing the sensing capability of an optical sensor. However, for most optical sensors, simple and straightforward methods of introducing an aqueous analyte to the device, such as applying droplets or spin-coating, cannot achieve targeted delivery of analyte molecules to hot spots. Instead, analyte molecules are usually distributed across the entire device surface, so the majority of the molecules do not experience enhanced field intensity. Here, we present a nanophotonic sensor design with passive molecule trapping functionality. When an analyte solution droplet is introduced to the sensor surface and gradually evaporates, the device structure can effectively trap most precipitated analyte molecules in its hot spots, significantly enhancing the sensor spectral response and sensitivity performance. Specifically, our sensors produce a reflection change of a few percentage points in response to trace amounts of the amino-acid proline or glucose precipitate with a picogram-level mass, which is significantly less than the mass of a molecular monolayer covering the same measurement area. The demonstrated strategy for designing optical sensor structures may also be applied to sensing nano-particles such as exosomes, viruses, and quantum dots., Photonic sensors: trapping analytes by digging into nano-trenches An innovative sensor can make it easier to use infrared light for label-free, picogram-scale detection of amino acids and other molecules. Photonic sensors avoid the need for large quantities of analytes by using nanoscale gap structures to trap targets and subject them to ultrahigh optical fields. Peter Liu and colleagues at the State University of New York at Buffalo in the United States have developed a microchip that naturally drives molecules into nanoscale gap regions. The team fabricated arrays where aluminum ribbons overhang narrower strips of insulating crystals. When a drop of test solution is placed onto the chip and left to evaporate, surface tension creates concave profiles that concentrate molecules under the aluminum layers. The resonant frequencies within this device’s “nano-trenches” can be tuned to specific molecular targets by tweaking the array’s geometric parameters.

We demonstrated a high-performance SEIRAS sensor based on nano-patch antennas for sensing monolayer analyte molecules sandwiched between liquid gallium and gold nano-strips. Close to 10% molecular vibrational absorption due to monolayer 1-octadecanethiol was achieved experimentally.

We demonstrate a high-sensitivity mid-infrared molecular absorption spectroscopy- based biomolecular sensor, which employs nanostructures for passively concentrating and trapping analyte molecules in a drying solution to photonic hotspots where optical fields are highly enhanced.

We experimentally demonstrate a nanophotonic biomolecular sensor which can passively concentrate and trap biomolecules in a drying analyte solution to regions of device structures where the field is highly enhanced, leading to improved sensing performance.

A periodic graphene anti-dot array integrated with self-aligned gold disks for enhancing interactions between terahertz graphene surface plasmons and incident light is demonstrated. Experimental results show enhancement of the resonant transmission modulation by ∼3 times.

Plasmonic dark modes are not easy to be observed in the far field due to their weak photon emission. By contrast, it has been shown that a dark mode can be excited effectively by a near-field source such as an electron beam. In this Letter, we show theoretically that the photon emission from the monopole-like dark mode supported on a plasmonic nano-disc could be unexpectedly strong when excited by an electron beam through its hole. Even though this monopole mode is considered to be dark, it is found that the emission can be even "brighter" than the dipolar bright modes when the electron speed is higher than 0.6c. Due to the high conversion efficiency from electron energy loss to photon energy, the results could also suggest an optical method for the detection of high-energy electrons passing through the hole with negligible changes in electron speed.