Spin angular momentum of light is vital to investigate enantiomers characterized by circular dichroism (CD), widely adopted in biology, chemistry, and material science. However, to discriminate chiral materials with multiscale features, CD spectroscopy normally requires wavelength-swept laser sources as well as wavelength-specific optical accessories. Here, we experimentally demonstrate an orbital-angular-momentum-assisted approach to yield chiroptical signals with monochromatic light. The gigantic vortical differential scattering (VDS) of ∼120% is achieved on intrinsically chiral microstructures fabricated by femtosecond laser. The VDS measurements can robustly generate chiroptical properties on microstructures with varying geometric features (e.g., diameters and helical pitches) and detect chiral molecules with high sensitivity. This VDS scheme lays a paradigm-shift pavement toward efficiently chiroptical discrimination of multiscale chiral structures with photonic orbital angular momentum. It simplifies and complements the conventional CD spectroscopy, opening possibilities for measuring weak optical chirality, especially on mesoscale chiral architectures and macromolecules.

A planar metamaterial structure has been designed to obtain surface plasmon-induced-transparency (PIT) effect, which is composed of a nanodisk sandwiched between double rods. From theoretical perspective, the three-level plasmonic system has been utilized to analyze the near-field coupling mechanism. Besides, the simulation results show that PIT resonance can be tailored by structure parameters. Particularly, when the length of the rods is more than twice of the diameter of the disk, two PIT windows are generated simultaneously, based on the coupling between the bright mode of the nanodisk and two multipole dark modes of rods. Furthermore, a metamaterial structure, composed by a disk and two pairs of nanorods, is suggested to achieve the polarization-independent plasmon-induced-transparency effect. As a result, this work shows great application prospect in the area of compact optical devices, such as multiband tunable filters, plasmonic switches, and slow light devices.

SERS properties of three-dimensional AuAg ANPs/G/AuAg ANPs SHNS.

In article number 1907377, Dong Wu, Li Zhang, and co-workers print hydrogel micro-flowers in the spatiotemporal domain via femtosecond laser direct writing. The 4D printed architectures can respond to environmental stimuli with high speed. Complex shape-morphing with expansion, contraction, twisting, and curling can be achieved by the proposed biomimetic 4D printing of hydrogels at the microscale.

Circular dichroism (CD) is widely used in bio-sensing, chemical analysis, and negative refraction. However, a concise method is required to enhance CD in planar chiral plasmonic nanostructures. In this work, graphene ribbons (GRs) are introduced in planar h-shaped-metal chiral nanostructures (PHCNs) to enhance CD. Calculated results show that the absorption spectra of PHCNs are differently enhanced because of the plasmonic coupling between PHCNs and GRs under different circularly polarized lights, thereby leading to CD enhancement. The loss distributions of PHCNs@GRs reveal that the loss is transferred from PHCNs to GRs. The current distributions of PHCNs@GRs are regarded as equivalent LC resonant circuits to explain the shift of the CD spectra by tuning the geometrical parameters of PHCNs@GRs. The results help design graphene-based chiral plasmonic nanostructures.

Circular dichroism (CD) is widely used in bio-sensing, pharmaceuticals, and molecular chemistry. Symmetry breaking is an important method of achieving CD signals. However, the relationship between the magnitude of CD and symmetry breaking remains unclear. In this study, we introduce nanorods into symmetric nanostructures comprising vertical Q-shaped nanostructure arrays (VQNAs) to prove the relativity of the symmetry breaking. The numerical simulations results show that the CD spectra of VQNAs present four modes in the visible spectrum. The coupling between nanorods differs under left- and right-handed circular polarized illuminations, leading to the production of the CD. The CD magnitude is not monotonic when the parameters of VQNAs change, and it is the largest for the structure at an appropriate scale. Besides, VQNAs have stable optical properties. Results can help to understand more deeply the CD mechanism produced by symmetry breaking, and design chiral plasmonic nanostructures.

Botanical systems have evolved the intriguing ability to respond to diverse stimuli due to long‐term survival competition. Mimicking these dynamic behaviors has greatly advanced the developments in wide fields ranging from soft robotics, precision sensors to drug delivery and biomedical devices. However, realization of stimuli‐responsive components at the microscale with high response speed still remains a significant challenge. Herein, the miniature biomimetic 4D printing of pH‐responsive hydrogel is reported in spatiotemporal domain by femtosecond laser direct writing. The dimension of the printed architectures is at the microscale (<10 2 µm) and the response speed is reduced down to subsecond level (<500 ms). Shape transformation with multiple degrees of freedom is accomplished by taking advantage of pH‐triggered expansion, contraction, and torsion. Biomimetic complex shape‐morphing is enabled by adopting flexible scanning strategies. In addition, application of this 4D‐printed micro‐architecture in selective micro‐object trapping and releasing is demonstrated, showcasing its possibilities in micromanipulation, single‐cell analysis, and drug delivery.

Here, we successfully synthesized silver-coated gold nanorods (Au@Ag NRs) via a facile wet chemical method. The catalytic property of Au@Ag NRs in water solution was much better than that of Au NRs in water solution. To obtain high catalytic properties, we self-assembled a single-layer Au@Ag NR array by evaporation on a silicon wafer. The catalytic activity of the Au@Ag NR array was probed using the reduction of 4-nitrothiophenol. The reaction processes were monitored and identified through in situ surface-enhanced Raman spectroscopy based on the confocal Raman microscope system. This study provides a simple and fast method to improve the catalytic property of the noble nanoparticles. (C) 2020 Elsevier B.V. All rights reserved.

Circular dichroism (CD) is useful in polarization conversion, negative refraction chemical analysis, and bio-sensing. To achieve strong CD signals, researchers constantly break the symmetry of nanostructures. However, how to further enhance the CD based on a new mechanism has become a new challenge in this field. In this work, a hybrid plasmonic chiral system composed of an array of graphene ribbons (GRs) over h-shaped sliver chiral nanostructures (HSCNs) is theoretically investigated. Results demonstrate that the plasmonic coupling between HSCNs and GRs results in different enhanced absorptions for different circularly polarized lights. The absorbance of right circularly polarized light is enhanced to perfect absorption; the absorption of left circularly polarized light is enhanced weakly. It leads to the CD effect of HSCNs@GRs approaching 88%. The loss distributions of HSCNs and HSCNs@GRs reveal that the absorption is enhanced and transferred from HSCNs to GRs. Moreover, the current distributions of HSCNs@GRs are simplified to equivalent LC resonant circuits, which can qualitatively explain the change of CD signals by tuning geometrical parameters of HSCNs@GRs. The findings of this work provide a new method of enhancing chirality and benefit the design of graphene-based chiral optoelectronic devices.

Induced circular dichroism (ICD) is found between plasmonic nanostructures and chiral molecules, where at least one of them is chiral. However, it is a great challenge to generate ICD only through achiral structures with the simple coupling model. Here, we demonstrate that ICD is approximately contributed by the cross-electromagnetic coupling between equivalent electric dipole moments and magnetic dipole moments for two achiral plasmon nanostructures. To prove electromagnetic couplings between different wavebands, graphene belts are introduced into plasmon nanostructures composing achiral metal-nanorods with graphene-nanobelt arrays (AMGAs). Results showed that ICD signals are achieved in a near-infrared band of metal resonance and a micron band of graphene resonance. Near-field charge distributions of AMGAs reveal the coupling effect between metal-nanorods and graphene-nanobelts. The handedness of AMGAs can be actively controlled by adjusting the Fermi levels of graphene-nanobelts; the strength and resonant wavelength of ICD can be tuned by adjusting the geometric parameters of AMGAs. Besides, AMGAs can enhance the CD signal of chiral molecules with different handedness. The maximum enhancement factor of chiral molecules could reach up to 800 times in a near-infrared band and 600 times in a micron band. These results are helpful to design dynamically tunable chiral sensors in biological monitoring and analytical chemistry.

Using Janus structures to realize shape transformation is an important method. Here, we present an approach which prepares geometry-switchable Janus micropillars by controlling scanning times of femtosecond laser on a pH -sensitive hydrogel. The applications of the proposed method in encryption, decryption, and display of information arc explored. Results show that these micropillars exhibit reversible structural deformation when the pH of the aqueous environment is changed. Because the laser printing technique is highly flexible, the spatial arrangements, pillar heights, and bending directions of micropillars can be readily controlled. Thus, patterns with variable spatial arrangement can be realized.

Circular dichroism (CD) induced by spin angular momentum of light is vital to investigate the chirality of microscopic objects such as molecules, proteins and metamaterials. However, orbital angular momentum (OAM) of light failed to directly implement an interaction with chiral molecules, which remains poorly understood. Even with the enhancement of unique plasmonic nanoparticle aggregates, the helical dichroism (HD) is still at a small level of 0.6 Here, we experimentally report the direct observation of a giant HD at the level of 120 Our results reveal a strong interaction between OAM beams and chiral microstructures in terms of their distinct reflectance, resulting in sign-opposite HD values to distinguish their chirality. Such unique HD phenomenon is investigated experimentally under various diameters and helical pitches of chiral structures, showing the robust performance. This HD technique can widely extend the responding areas of chiral spectroscopy in biology, material science and nanotechnology.

Self-assembly induced by capillary force is abundant in nature and has been widely used in fabrication as a bottom-up method. Here a rapid and flexible method for achieving an even number of furcate slanted micropillars by single-exposure under a spatial phase modulated laser beam is reported, which is produced by designing a superimposed hologram with opposite topological charges to split the incident beam into several equal-weighting sectors. These furcate micropillars with intentional spatial arrangement can be directed to capillary-assisted self-assembly process for generating designable hierarchical functional arrays. Due to the slanted characteristic of micropillars (8 degrees-13 degrees), the assembled arrays are very stable and can be used as an effective tool for trapping SiO2 particles to form honeycomb patterns with an ultrahigh trapping ratio (>90%), which can image as a microlens array. The investigation reveals that micropillars with a height of 6 mu m exhibit the high trapping ratio of particles, which maintain a fine imaging performance. The fast fabrication (more than 2 orders of magnitude enhancement) of furcate slanted pillars paves an avenue for developing innovative microoptics, microfluidics and biological scaffold engineering.

In this paper, we demonstrate that the superposition of two vortex beams with controlled topological charges can be realized by integrating two holographic plates with blazed grating. First, the holographic plate with blazed grating was designed and fabricated by laser direct writing for generating well-separated vortex beam. Then, the relationship between the periods of blazed grating and the discrete angles of vortex beams was systemically investigated. Finally, through setting the discrete angle and different revolving direction of the holographic plates, the composite fork-shaped field was realized by the superposition of two vortex beams in a particular position. The topological charges of composite fork-shaped field (l = 1, 0, 3, and 4) depend on the topological charges of compositional vortex beams, which are well agreed with the theoretical simulation. The method opens up a wide range of opportunities and possibilities for applying in optical communication, optical manipulations, and photonic integrated circuits.

AbstractSelf‐assembly induced by capillary force is abundant in nature and has been widely used in fabrication as a bottom‐up method. Here a rapid and flexible method for achieving an even number of furcate slanted micropillars by single‐exposure under a spatial phase modulated laser beam is reported, which is produced by designing a superimposed hologram with opposite topological charges to split the incident beam into several equal‐weighting sectors. These furcate micropillars with intentional spatial arrangement can be directed to capillary‐assisted self‐assembly process for generating designable hierarchical functional arrays. Due to the slanted characteristic of micropillars (8°–13°), the assembled arrays are very stable and can be used as an effective tool for trapping SiO2 particles to form honeycomb patterns with an ultrahigh trapping ratio (>90%), which can image as a microlens array. The investigation reveals that micropillars with a height of 6 µm exhibit the high trapping ratio of particles, which maintain a fine imaging performance. The fast fabrication (more than 2 orders of magnitude enhancement) of furcate slanted pillars paves an avenue for developing innovative microoptics, microfluidics and biological scaffold engineering.