Enantioselective Optical Trapping of Multiple Pairs of Enantiomers by Focused Hybrid Polarized Beams.

Enantiomers (opposite chiral molecules) usually exhibit different effects when interacting with chiral agents, thus the identification and separation of enantiomers are of importance in pharmaceuticals and agrochemicals. Here an optical approach is proposed to enantioselective trapping of multiple pairs of enantiomers by a focused hybrid polarized beam. Numerical results indicate that such a focused beam shows multiple local optical chirality of opposite signs in the focal plane, and can trap the corresponding enantiomers near the extreme value of optical chirality density according to the handedness of enantiomers. The number and positions of trapped enantiomers can be changed by altering the value and sign of polarization orders of hybrid polarized beams, respectively. The key to realizing enantioselective optical trapping of enantiomers is that the chiral optical force exerted on enantiomers in this focused field is stronger than the achiral optical force. The results provide insight into the optical identification and separation of multiple pairs of enantiomers and will find applications in chiral detection and sensing.

Creating tunable lateral optical forces through multipolar interplay in single nanowires.

The concept of lateral optical force (LOF) is of general interest in optical manipulation as it releases the constraint of intensity gradient in tightly focused light, yet such a force is normally limited to exotic materials and/or complex light fields. Here, we report a general and controllable LOF in a nonchiral elongated nanoparticle illuminated by an obliquely incident plane wave. Through computational analysis, we reveal that the sign and magnitude of LOF can be tuned by multiple parameters of the particle (aspect ratio, material) and light (incident angle, direction of linear polarization, wavelength). The underlying physics is attributed to the multipolar interplay in the particle, leading to a reduction in symmetry. Direct experimental evidence of switchable LOF is captured by polarization-angle-controlled manipulation of single Ag nanowires using holographic optical tweezers. This work provides a minimalist paradigm to achieve interface-free LOF for optomechanical applications, such as optical sorting and light-driven micro/nanomotors.

Analysis and circuit implementation of a non-equilibrium fractional-order chaotic system with hidden multistability and special offset-boosting.

In order to obtain a system of higher complexity, a new fractional-order chaotic system is constructed based on the Sprott system. It is noteworthy that the system has no equilibrium point yet exhibits chaotic properties and has rich dynamical behavior. Its basic properties are analyzed by Lyapunov exponents, phase diagrams, and smaller alignment index tests. The change of its state is observed by changing parameters and order, during which the new system is found to have intermittent chaos phenomena. Surprisingly, the new proposed system has a special offset-boosting phenomenon, where only a boosting-controller makes the system undergo a multi-directional offset, and the shape of the generated hidden attractor changes. In addition, changing the initial value brings kinds of coexisting attractors in the system, which proves the existence of multistability. Because the new system is very sensitive to the initial value, the complexity of the new system is calculated based on the complexity algorithm, and the initial value with higher complexity is gained by contrast. Finally, the field programmable gate array is used to implement the actual circuit of the new system to verify its feasibility. This system provides an example for the study of fractional-order chaotic systems and a complex system for fractional-order chaotic applications.

Characterization of Mechanical, Electrical and Thermal Properties of Bismaleimide Resins Based on Different Branched Structures.

Bismaleimide (BMI) resin is an excellent performance resin, mainly due to its resistance to the effect of heat and its insulating properties. However, its lack of toughness as a cured product hampers its application in printed circuit boards (PCBs). Herein, a branched structure via Michael addition was introduced to a BMI system to reinforce its toughness. Compared with a pure BMI sample, the flexural strength of the modified BMI was enhanced, and its maximum value of 189 MPa increased by 216%. The flexural modulus of the cured sample reached 5.2 GPa. Using a scanning electron microscope, the fracture surfaces of BMI samples and a transition from brittle fracture to ductile fracture were observed. Furthermore, both the dielectric constant and the dielectric loss of the cured resin decreased. The breakdown field strength was raised to 37.8 kV/mm and the volume resistivity was improved to varying degrees. Consequently, the resulting modified BMI resin has the potential for wide application in high-frequency and low-dielectric resin substrates, and the modified BMI resin with a structure including three different diamines can meet the needs of various applications.

Reversible lateral optical force on phase-gradient metasurfaces for full control of metavehicles.

Photonics is currently undergoing an era of miniaturization thanks in part to two-dimensional (2D) optical metasurfaces. Their ability to sculpt and redirect optical momentum can give rise to an optical force, which acts orthogonally to the direction of light propagation. Powered by a single unfocused light beam, these lateral optical forces (LOFs) can be used to drive advanced metavehicles and are controlled via the incident beam's polarization. However, the full control of a metavehicle on a 2D plane (i.e. forward, backward, left, and right) with a sign-switchable LOF remains a challenge. Here we present a phase-gradient metasurface route for achieving such full control while also increasing efficiency. The proposed metasurface is able to deflect a normally incident plane wave in a traverse direction by modulating the plane wave's polarization, and results in a sign-switchable recoil LOF. When applied to a metavehicle, this LOF enables a level of motion control that was previously unobtainable.

Observation of high-order imaginary Poynting momentum optomechanics in structured light.

The imaginary Poynting momentum (IPM) of light has been captivated as an unusual origin of optical forces. However, the IPM force is predicted only for dipolar magnetoelectric particles that are hardly used in optical manipulation experiments. Here, we report a whole family of high-order IPM forces for not only magnetoelectric but also generic Mie particles, assisted with their excited higher multipoles within. Such optomechanical manifestations derive from a nonlocal contribution of the IPM to the optical force, which can be remarkable even when the incident IPM is small. We observe the high-order optomechanics in a structured light beam, which, despite carrying no angular momentum, is able to set normal microparticles into continuous rotation. Our results provide unambiguous evidence of the ponderomotive nature of the IPM, expand the classification of optical forces, and open new possibilities for levitated optomechanics and micromanipulations.

Identification and separation of chiral particles by focused circularly polarized vortex beams.

The identification and separation of chiral substances are of importance in the biological, chemical, and pharmaceutical industries. Here, we demonstrate that a focused circularly polarized vortex beam can, in the focal plane, selectively trap and rotate chiral dipolar particles via radial and azimuthal optical forces. The handedness and topological charge of the incident beam have strong influence on identifying and separating behavior: left- and right-handed circular polarizations lead to opposite effects on the particle of trapping and rotating, while the sign of topological charge will change the particle's rotation direction. Such effects are a direct result of the handedness and topological charge manifesting themselves in the directions of the spin angular momentum (SAM) and Poynting vector. The research provides insight into the chiral light-matter interaction and may find potential application in the identification and separation of chiral nanoparticles.

Spirally rotating particles with structured beams generated by phase-shifted zone plates.

The emerging field of structured beams has led to optical manipulation with tremendous progress. Beyond various methods for structured beams, we use phase-shifted zone plates known as beam-shaping diffractive optical elements to generate beams whose phase exclusively or both phase and intensity are twisted along a curve. These beams can trap and guide particles on open curved trajectories for continuous motion, not necessarily requiring a closed symmetric intensity distribution. We show the feasibility and versatility of the proposed method as a promising technique in optical manipulation in which the trajectory of the spiral rotation and the rate of rotation of trapped particles can be controlled.

Axial resolution enhancement for planar Airy beam light-sheet microscopy via the complementary beam subtraction method.

Airy beam light-sheet illumination can extend the field of view (FOV) of light-sheet fluorescence microscopy due to the unique propagation properties of non-diffraction and self-acceleration. However, the side lobes create undesirable out-of-focus background, leading to poor axial resolution and low image contrast. Here, we propose an Airy complementary beam subtraction (ACBS) method to improve the axial resolution while keeping the extended FOV. By scanning the optimized designed complementary beam that has two main lobes (TML), the generated complementary light-sheet has almost identical intensity distribution to that of the planar Airy light-sheet except for the central lobe. Subtraction of the two images acquired by double exposure respectively using the planar Airy light-sheet and the planar TML light-sheet can effectively suppress the influence of the out-of-focus background. The axial resolution improves from ∼4µm to 1.2 µm. The imaging performance was demonstrated by imaging specimens of aspergillus conidiophores and GFP labeled mouse brain section. The results show that the ACBS method enables the Airy beam light-sheet fluorescence microscopy to obtain better imaging quality.

Construction of Lattice Strain in Bimetallic Nanostructures and Its Effectiveness in Electrochemical Applications.

Bimetallic nanocrystals (NCs), associated with various surface functions such as ligand effect, ensemble effect, and strain effect, exhibit superior electrocatalytic properties. The stress-induced surface strain effect can alter binding strength between the surface active sites and reactants as well as their intermediates, and the electrochemical performance of bimetallic NCs can be significantly facilitated by the lattice-strain modification via their morphologies, sizes, shell-thickness, surface defectiveness as well as compositions. In this review, an overview of fundamental principles, characterization techniques, and quantitative determination of the surface lattice strain is provided. Various strategies and synthesis efforts on creating lattice-strain-engineered bimetallic NCs, including the de-alloying process, atomic layer-by-layer deposition, thermal treatment evolution, one-pot synthesis, and other efforts are also discussed. It is further outlined how the lattice strain effect promotes electrochemical catalysis through the selected case studies. The reactions on oxygen reduction reaction, small molecular oxidation, water splitting reaction, and electrochemical carbon dioxide reduction reactions are focused. In particular, studies of lattice strain arisen from core-shell nanostructure and defectiveness are highlighted. Lastly, the potential challenges are summarized and the prospects of lattice-strain-based engineering on bimetallic nanocatalysts with suggestion and guidance of the future electrocatalyst design are envisioned.

Heterogeneous Ni3S2@FeNi2S4@NF nanosheet arrays directly used as high efficiency bifunctional electrocatalyst for water decomposition.

Developing and designing bifunctional electrocatalysts are very important for the production of hydrogen from water electrolysis. The reasonable interface modulation can effectively lead to the optimization of electronic configuration through the interface electron transfer in the heterostructures and thus resulting in the enhanced efficiency. In this work, self-supported and heterogeneous interface-rich Ni3S2@FeNi2S4@NF electrocatalyst for overall water splitting was designed and prepared through a controllable step-wise hydrothermal process. Density functional theory calculations suggest that heterogeneous interface formed between Ni3S2 and FeNi2S4 can optimize the Gibbs free energy for H* adsorption (ΔGH*). Benefiting from the open structure of the nanosheet arrays, the abundant heterogeneous interfaces in Ni3S2@FeNi2S4@NF composite, the positive synergistic effect between Ni3S2 and FeNi2S4, and the good conductivity of foamed nickel (NF) substrate, the optimized Ni3S2@FeNi2S4@NF nanoarray catalyst displayed excellent electrocatalytic activities, the overpotential is only 83 mV and 235 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at 10 mA cm-2, respectively. Importantly, an alkaline electrolyser directly using the Ni3S2@FeNi2S4@NF as both the anode and cathode achieved an ultralow cell voltage of 1.46 V, accompanied by outstanding stability. The performance is better than that of most other transition-metal sulfides electrocatalysts. This work may provide a useful strategy for reasonably regulating heterogeneous interfaces to effectively improve the performance of materials, thus accelerating the practical application of transition-metal sulfides electrocatalysts for overall water splitting.

Direct axial plane imaging of particle manipulation with nondiffracting Bessel beams.

Optical manipulation with nondiffracting beams has been attracting great interest and finding widespread applications in many fields such as chemistry, physics, and biomedicine. Generally, optical manipulation is conducted in an optical microscopy system, which, in general, only allows for imaging motions of particles in the transverse plane, rendering the observation of dynamics processes occurring in the axial plane impractical. We propose and demonstrate an optical manipulation system that incorporates an axial plane imaging module. With this system, the trapping behavior in the transverse plane and the transportation process in the axial plane of a particle immersed in a Bessel beam were acquired simultaneously in real time.

Rapid Image Reconstruction of Structured Illumination Microscopy Directly in the Spatial Domain.

Super-resolution structured illumination microscopy (SIM) routinely performs image reconstruction in the frequency domain using an approach termed frequency-domain reconstruction (FDR). Due to multiple Fourier transforms between the spatial and frequency domains, SIM suffers from low reconstruction speed, constraining its applications in real-time, dynamic imaging. To overcome this limitation, we developed a new method for SIM image reconstruction, termed spatial domain reconstruction (SDR). SDR is intrinsically simpler than FDR, does not require Fourier transforms and the theory predicts it to be a rapid image reconstruction method. Results show that SDR reconstructs a super-resolution image 7-fold faster than FDR, producing images that are equal to either FDR or the widely-used FairSIM. We provide a proof-of-principle using mobile fluorescent beads to demonstrate the utility of SDR in imaging moving objects. Consequently, replacement of the FDR approach with SDR significantly enhances SIM as the desired method for live-cell, instant super-resolution imaging. This means that SDR-SIM is a "What You See Is What You Get" approach to super-resolution imaging.

Extended field of view of light-sheet fluorescence microscopy by scanning multiple focus-shifted Gaussian beam arrays.

Light-sheet fluorescence microscopy (LSFM) facilitates high temporal-spatial resolution, low photobleaching and phototoxicity for long-term volumetric imaging. However, when a high axial resolution or optical sectioning capability is required, the field of view (FOV) is limited. Here, we propose to generate a large FOV of light-sheet by scanning multiple focus-shifted Gaussian beam arrays (MGBA) while keeping the high axial resolution. The positions of the beam waists of the multiple Gaussian beam arrays are shifted in both axial and lateral directions in an optimized arranged pattern, and then scanned along the direction perpendicular to the propagation axis to form an extended FOV of light-sheet. Complementary beam subtraction method is also adopted to further improve axial resolution. Compared with the single Gaussian light-sheet method, the proposed method extends the FOV from 12 µm to 200 µm while sustaining the axial resolution of 0.73 µm. Both numerical simulation and experiment on samples are performed to verify the effectiveness of the method.

Synthesis of Core@Shell Cu-Ni@Pt-Cu Nano-Octahedra and Their Improved MOR Activity.

Fabrication of 3d metal-based core@shell nanocatalysts with engineered Pt-surfaces provides an effective approach for improving the catalytic performance. The challenges in such preparation include shape control of the 3d metallic cores and thickness control of the Pt-based shells. Herein, we report a colloidal seed-mediated method to prepare octahedral CuNi@Pt-Cu core@shell nanocrystals using CuNi octahedral cores as the template. By precisely controlling the synthesis conditions including the deposition rate and diffusion rate of the shell-formation through tuning the capping ligand, reaction temperature, and heating rate, uniform Pt-based shells can be achieved with a thickness of <1 nm. The resultant carbon-supported CuNi@Pt-Cu core@shell nano-octahedra showed superior activity in electrochemical methanol oxidation reaction (MOR) compared with the commercial Pt/C catalysts and carbon-supported CuNi@Pt-Cu nano-polyhedron counterparts.

Optical separation and discrimination of chiral particles by vector beams with orbital angular momentum.

Chirality describes a reduced symmetry and abounds in nature. The handedness-dependent response usually occurs only when a chiral object interacts with another chiral entity. Light carrying orbital angular momentum (OAM) is inherently chiral due to the helical wave front. Here, we put forward a scheme that enables optical separation and simultaneous discrimination of single chiral particles using focused vector beams with OAM. Such focused vector vortex beams carrying radial-splitting optical chirality can selectively trap one enantiomer inside or outside the intensity maxima depending on the sign of the OAM. The particles with different chirality parameters can be trapped on different orbits and experience enhanced orbital motion. Moreover, the magnitude of OAM as well as the size of particle plays an important role in the chiral separation and discrimination. In addition to particle manipulation, the discussion of OAM in chiral light-matter interactions has potential application in, for example, optical enantioseparation or chiral detection.

Accelerating triangle-like singular beam.

We demonstrate a type of singular beam that accelerates along a parabolic trajectory and has a cross-section intensity pattern exhibiting a dark central region surrounded by multiple rings with the innermost (main) ring resembling an equilateral triangle. The key to creating such beams is to replace the standard triangle with a rounded one, made up of six circular arcs connected end to end. The individual input phase mask for each arc can be analytically computed, and the whole input phase mask for the beam is thus obtained by piecing together these individual phases. Furthermore, the continuity of field forces of these triangle-like modes is discrete; that is, an index similar to the topological charge of vortex beams arises. Numerical results show that the energy flow in the beam's cross section circulates around the dark center along the triangle-like main ring, suggesting a possible application in orbiting particles along an irregular path.

Compact optical module to generate arbitrary vector vortex beams.

We demonstrated a compact optical module that is capable of efficiently generating vector vortex beams (VVB). With this device, a linearly polarized input beam can be converted into a vector beam with arbitrary spatial polarization and phase distributions, accompanied by an energy utilization up to 61%. Equally important, the area utilization of the spatial light modulator, a key component in the device, is as high as 65.5%. With the designed vector-vortex-beam-generation module, several types of VVBs with different vortex topological charges and spatial polarization distributions were created experimentally. This device may find applications in optical tweezers, laser machining, and so on.

Generation of controllable chiral optical fields by vector beams.

Chirality is common in nature, describing not only the geometrical property of a three-dimensional object, but also an intrinsic feature of an optical field. Chiral optical fields are attracting increasing attention due to their potential applications in chiral light-matter interaction. Here we demonstrate a strategy to realize a controllable chiral optical field by tightly focusing two tailored vector beams in a 4π optical microscopic system. By modulating the wavefronts of the incident vector beams with appropriately designed phase masks, a chiral optical field with multiple spots carrying switchable handedness or controllable chirality can be generated. The location, the number and the handedness of such chiral spots can be arbitrarily adjusted depending on the actual application requirements. In addition to trapping and manipulating multiple particles, this controllable chiral optical field may find applications in enantioselective separation, chiral detection and chiral sensing at the nanoscale.

Rapid tilted-plane Gerchberg-Saxton algorithm for holographic optical tweezers.

Benefitting from the development of commercial spatial light modulator (SLM), holographic optical tweezers (HOT) have emerged as a powerful tool for life science, material science and particle physics. The calculation of computer-generated holograms (CGH) for generating multi-focus arrays plays a key role in HOT for trapping of a bunch of particles in parallel. To realize dynamic 3D manipulation, we propose a new tilted-plane GS algorithm for fast generation of multiple foci. The multi-focal spots with a uniformity of 99% can be generated in a tilted plane. The computation time for a CGH with 512×512 pixels is less than 0.1 second. We demonstrated the power of the algorithm by simultaneously trapping and rotating silica beads with a 7×7 spots array in three dimensions. The presented algorithm is expected as a powerful kernel of HOT.