Showing papers by "Minghui Hong published in 2015"

Temporal full-colour tuning through non-steady-state upconversion

Abstract: Developing light-harvesting materials with tunable emission colours has always been at the forefront of colour display technologies. The variation in materials composition, phase and structure can provide a useful tool for producing a wide range of emission colours, but controlling the colour gamut in a material with a fixed composition remains a daunting challenge. Here, we demonstrate a convenient, versatile approach to dynamically fine-tuning emission in the full colour range from a new class of core-shell upconversion nanocrystals by adjusting the pulse width of infrared laser beams. Our mechanistic investigations suggest that the unprecedented colour tunability from these nanocrystals is governed by a non-steady-state upconversion process. These findings provide keen insights into controlling energy transfer in out-of-equilibrium optical processes, while offering the possibility for the construction of true three-dimensional, full-colour display systems with high spatial resolution and locally addressable colour gamut.

Catenary optics for achromatic generation of perfect optical angular momentum

Abstract: The catenary is the curve that a free-hanging chain assumes under its own weight, and thought to be a “true mathematical and mechanical form” in architecture by Robert Hooke in the 1670s, with nevertheless no significant phenomena observed in optics. We show that the optical catenary can serve as a unique building block of metasurfaces to produce continuous and linear phase shift covering [0, 2π], a mission that is extremely difficult if not impossible for state-of-the-art technology. Via catenary arrays, planar optical devices are designed and experimentally characterized to generate various kinds of beams carrying orbital angular momentum (OAM). These devices can operate in an ultra-broadband spectrum because the anisotropic modes associated with the spin-orbit interaction are almost independent of the incident light frequency. By combining the optical and topological characteristics, our approach would allow the complete control of photons within a single nanometric layer.

Switchable Ultrathin Quarter-wave Plate in Terahertz Using Active Phase-change Metasurface.

Abstract: Metamaterials open up various exotic means to control electromagnetic waves and among them polarization manipulations with metamaterials have attracted intense attention. As of today, static responses of resonators in metamaterials lead to a narrow-band and single-function operation. Extension of the working frequency relies on multilayer metamaterials or different unit cells, which hinder the development of ultra-compact optical systems. In this work, we demonstrate a switchable ultrathin terahertz quarter-wave plate by hybridizing a phase change material, vanadium dioxide (VO2), with a metasurface. Before the phase transition, VO2 behaves as a semiconductor and the metasurface operates as a quarter-wave plate at 0.468 THz. After the transition to metal phase, the quarter-wave plate operates at 0.502 THz. At the corresponding operating frequencies, the metasurface converts a linearly polarized light into a circularly polarized light. This work reveals the feasibility to realize tunable/active and extremely low-profile polarization manipulation devices in the terahertz regime through the incorporation of such phase-change metasurfaces, enabling novel applications of ultrathin terahertz meta-devices.

Shaping a Subwavelength Needle with Ultra-long Focal Length by Focusing Azimuthally Polarized Light

Abstract: Flat optics, which could planarize and miniaturize the traditional optical elements, possesses the features of extremely low profile and high integration for advanced manipulation of light. Here we proposed and experimentally demonstrated a planar metalens to realize an ultra-long focal length of ~240λ with a large depth of focus (DOF) of ~12λ, under the illumination of azimuthally polarized beam with vortical phase at 633 nm. Equally important is that such a flat lens could stably keep a lateral subwavelength width of 0.42λ to 0.49λ along the needle-like focal region. It exhibits one-order improvement in the focal length compared to the traditional focal lengths of 20~30λ of flat lens, under the criterion of having subwavelength focusing spot. The ultra-long focal length ensures sufficient space for subsequent characterization behind the lens in practical industry setups, while subwavelength cross section and large DOF enable high resolution in transverse imaging and nanolithography and high tolerance in axial positioning in the meantime. Such planar metalens with those simultaneous advantages is prepared by laser pattern generator rather than focused ion beam, which makes the mass production possible.

An ultrathin terahertz quarter-wave plate using planar babinet-inverted metasurface

Abstract: Metamaterials promise an exotic approach to artificially manipulate the polarization state of electromagnetic waves and boost the design of polarimetric devices for sensitive detection, imaging and wireless communication. Here, we present the design and experimental demonstration of an ultrathin (0.29λ) terahertz quarter-wave plate based on planar babinet-inverted metasurface. The quarter-wave plate consisting of arrays of asymmetric cross apertures reveals a high transmission of 0.545 with 90 degrees phase delay at 0.870 THz. The calculated ellipticity indicates a high degree of polarization conversion from linear to circular polarization. With respect to different incident polarization angles, left-handed circular polarized light, right-handed circular polarized light and elliptically polarized light can be created by this novel design. An analytical model is applied to describe transmitted amplitude, phase delay and ellipticitiy, which are in good agreement with the measured and simulated results. The planar babinet-inverted metasurface with the analytical model opens up avenues for new functional terahertz devices design.

Engineering the Phase Front of Light with Phase-Change Material Based Planar lenses

Abstract: A novel hybrid planar lens is proposed to engineer the far-field focusing patterns. It consists of an array of slits which are filled with phase-change material Ge2Sb2Te5 (GST). By varying the crystallization level of GST from 0% to 90%, the Fabry-Perot resonance supported inside each slit can be spectrally shifted across the working wavelength at 1.55 µm, which results in a transmitted electromagnetic phase modulation as large as 0.56π. Based on this geometrically fixed platform, different phase fronts can be constructed spatially on the lens plane by assigning the designed GST crystallization levels to the corresponding slits, achieving various far-field focusing patterns. The present work offers a promising route to realize tunable nanophotonic components, which can be used in optical circuits and imaging applications.

Tunable near-infrared plasmonic perfect absorber based on phase-change materials

Abstract: A tunable plasmonic perfect absorber with a tuning range of similar to 650 nm is realized by introducing a 20 nm thick phase-change material Ge2Sb2Te5 layer into the metal-dielectric-metal configuration. The absorption at the plasmonic resonance is kept above 0.96 across the whole tuning range. In this work we study this extraordinary optical response numerically and reveal the geometric conditions which support this phenomenon. This work shows a promising route to achieve tunable plasmonic devices for multi-band optical modulation, communication, and thermal imaging. (C) 2015 Chinese Laser Press

Hierarchical Assembly of SnO2/ZnO Nanostructures for Enhanced Photocatalytic Performance.

Abstract: SnO2/ZnO hierarchical heterostructures have been successfully synthesized by combining electrospinning technique and hydrothermal method. Various morphologies of the secondary ZnO nanostructures including nanorods (NRs) and nanosheets (NSs) can be tailored by adding surfactants. Photocatalytic performance of the heterostructures was investigated and obvious enhancement was demonstrated in degradation of the organic pollutant, compared to the primary SnO2-based nanofibers (NFs) and bare ZnO. Furthermore, it was found that the H2 evolution from water splitting was achieved by photocatalysis of heterostructured nanocomposites after sulfurization treatment. This synthetic methodology described herein promises to be an effective approach for fabricating variety of nanostructures for enhanced catalytic applications. The heterostructured nanomaterials have considerable potential to address the environmental and energy issues via degradation of pollutant and generation of clean H2 fuel.

Conjugated polymer and drug co-encapsulated nanoparticles for Chemo- and Photo-thermal Combination Therapy with two-photon regulated fast drug release

Abstract: The spatial-temporal synchronization of photothermal therapy and chemotherapy is highly desirable for an efficient cancer treatment with synergistic effect. Herein, we developed a chemotherapeutic drug doxorubicin (DOX) and photothermal conjugated polymer (CP) co-loaded nanoplatform using a near-infrared (NIR) laser responsive amphiphilic brush copolymer as the encapsulation matrix. The obtained nanoparticles (NPs) exhibit good monodispersity and excellent stability, which can efficiently convert laser energy into thermal energy for photothermal therapy. Moreover, the hydrophobic polymer matrix bearing a number of 2-diazo-1,2-naphthoquinones (DNQ) moieties could be transformed to a hydrophilic one upon NIR two-photon laser irradiation, which leads to fast drug release. Furthermore, the surface modification of the NPs with cyclic arginine-glycine-aspartic acid (cRGD) tripeptide significantly enhances the accumulation of the NPs within integrin αvβ3 overexpressed cancer cells. The half-maximal inhibitory concentration (IC50) of the combination therapy is 13.7 μg mL−1, while the IC50 for chemotherapy and photothermal therapy alone is 147.8 μg mL−1 and 36.2 μg mL−1, respectively. The combination index (C.I.) is 0.48 (<1), which indicates the synergistic effect for chemotherapy and PTT. These findings provide an excellent NIR laser regulated nanoplatform for combined cancer treatment with synergistic effect due to the synchronous chemo- and photo-thermal therapy.

Super-long photonic nanojet generated from liquid-filled hollow microcylinder.

Abstract: Photonic nanojet (PNJ) from liquid-filled hollow microcylinder (LFHM) under a liquid immersion condition is numerically investigated based on the finite element method and physically analyzed with ray optics. Simulation and analysis results show that, by simultaneously introducing the immersed liquid and filled liquid, the propagation beam is greatly flattened, and super-long PNJs with decay length more than 100 times the illumination wavelengths are obtained in the outer near-field region of the LFHM. With the variation of the refractive index contrast between the filled and immersed-liquids, the properties of the PNJs, such as the focal distance, decay length, full width at half-maximum, and maximum light intensity can be flexibly tuned.

Modulation of photonic nanojets generated by microspheres decorated with concentric rings

Abstract: A novel design of decorating microsphere surface with concentric rings to modulate the photonic nanojet (PNJ) is investigated. By introducing the concentric ring structures into the illumination side of the microspheres, a reduction of the full width at half maximum (FWHM) intensity of the PNJ by 29.1%, compared to that without the decoration, can be achieved numerically. Key design parameters, such as ring number and depth, are analyzed. Engineered microsphere with four uniformly distributed rings etched at a depth of 1.2 μm and width of 0.25 μm can generate PNJ at a FWHM of 0.485 λ (λ = 400nm). Experiments were carried out by direct observation of the PNJ with an optical microscope under 405 nm laser illumination. As a result, shrinking of PNJ beam size of 28.0% compared to the case without the rings has been achieved experimentally. Sharp FWHM of this design can be beneficial to micro/nanoscale fabrication, optical super-resolution imaging, and sensing.

Plasmon-Induced Optical Anisotropy in Hybrid Graphene–Metal Nanoparticle Systems

Abstract: Hybrid plasmonic metal–graphene systems are emerging as a class of optical metamaterials that facilitate strong light-matter interactions and are of potential importance for hot carrier graphene-based light harvesting and active plasmonic applications. Here we use femtosecond pump–probe measurements to study the near-field interaction between graphene and plasmonic gold nanodisk resonators. By selectively probing the plasmon-induced hot carrier dynamics in samples with tailored graphene–gold interfaces, we show that plasmon-induced hot carrier generation in the graphene is dominated by direct photoexcitation with minimal contribution from charge transfer from the gold. The strong near-field interaction manifests as an unexpected and long-lived extrinsic optical anisotropy. The observations are explained by the action of highly localized plasmon-induced hot carriers in the graphene on the subresonant polarizability of the disk resonator. Because localized hot carrier generation in graphene can be exploited...

Laser Hybrid Micro/nano-structuring of Si Surfaces in Air and its Applications for SERS Detection

Abstract: Surface enhanced Raman spectroscopy (SERS) has been widely investigated as an effective technique for low-concentration bio-chemical molecules detection. A rapid two-step approach to fabricate SERS substrates with high controllability in ambient air is developed. Dynamic laser ablation directly creates microgroove on the Si substrate. Meanwhile, nanoparticles are synthesized via the nucleation of laser induced plasma species and the air molecules. It configures the Si surface into four different regions decorated with nanoparticles at different sizes. With Ag film coating, these nanoparticles function as hotspots for SERS. Microsquare arrays are fabricated on the Si surface as large-area SERS substrates by the laser ablation in horizontal and vertical directions. In each microsquare, it exhibits quasi-3D structures with randomly arranged and different shaped nanoparticles aggregated in more than one layer. With Ag film deposition, uniform SERS signals are obtained by detecting the 4-methylbenzenethiol molecules. The SERS signal intensity is determined by the size and shape distributions of the nanoparticles, which depend on the laser processing parameters. With the optimal laser fluence, the SERS signals show a uniform enhancement factor up to 5.5 × 106. This provides a high-speed and low-cost method to produce SERS substrates over a large area.

A highly efficient CMOS nanoplasmonic crystal enhanced slow-wave thermal emitter improves infrared gas-sensing devices

Abstract: The application of plasmonics to thermal emitters is generally assisted by absorptive losses in the metal because Kirchhoff's law prescribes that only good absorbers make good thermal emitters. Based on a designed plasmonic crystal and exploiting a slow-wave lattice resonance and spontaneous thermal plasmon emission, we engineer a tungsten-based thermal emitter, fabricated in an industrial CMOS process, and demonstrate its markedly improved practical use in a prototype non-dispersive infrared (NDIR) gas-sensing device. We show that the emission intensity of the thermal emitter at the CO(2) absorption wavelength is enhanced almost 4-fold compared to a standard non-plasmonic emitter, which enables a proportionate increase in the signal-to-noise ratio of the CO(2) gas sensor.

Tuning Interior Nanogaps of Double-shelled Au/Ag Nanoboxes for Surface-Enhanced Raman Scattering

Abstract: Double-shelled Au/Ag hollow nanoboxes with precisely controlled interior nanogaps (1 to 16 nm) were synthesized for gap-tunable surface-enhanced Raman scattering (SERS). The double-shelled nanoboxes were prepared via a two-step galvanic replacement reaction approach using Ag nanocubes as the templates, while 4-aminothiolphenol (4-ATP) as SERS probe molecules were loaded between the two shells. More than 10-fold enhancement of SERS is observed from the double-shelled nanoboxes than Ag nanocubes. In addition, the SERS of the double-shelled nanoboxes increase significantly with the decrease of gap size, consistent with the theoretical prediction that smaller gap size induces larger localized electromagnetic enhancement.

Dual-Microstructured Porous, Anisotropic Film for Biomimicking of Endothelial Basement Membrane.

Abstract: Human endothelial basement membrane (BM) plays a pivotal role in vascular development and homeostasis. Here, a bioresponsive film with dual-microstructured geometries was engineered to mimic the structural roles of the endothelial BM in developing vessels, for vascular tissue engineering (TE) application. Flexible poly(e-caprolactone) (PCL) thin film was fabricated with microscale anisotropic ridges/grooves and through-holes using a combination of uniaxial thermal stretching and direct laser perforation, respectively. Through optimizing the interhole distance, human mesenchymal stem cells (MSCs) cultured on the PCL film’s ridges/grooves obtained an intact cell alignment efficiency. With prolonged culturing for 8 days, these cells formed aligned cell multilayers as found in native tunica media. By coculturing human umbilical vein endothelial cells (HUVECs) on the opposite side of the film, HUVECs were observed to build up transmural interdigitation cell–cell contact with MSCs via the through-holes, leading...

Selective excitation of resonances in gammadion metamaterials for terahertz wave manipulation

Abstract: A gammadion terahertz (THz) metamaterial embedded with a pair of splits is experimentally investigated. By introducing the pair of splits at different arms, the transmitted amplitude at the resonance frequency can be manipulated from 61% to 24%. Broadband static resonance tunability from 1.11 to 1.51 THz is also demonstrated via varying the relative split positions at certain arms. The amplitude change and static resonance tunability are attributed to the introduced split pairs, which enable selective excitation of different resonance modes in the gammadion metamaterials. This work promises a new approach to design THz functional devices.

A frozen matrix hybrid optical nonlinear system enhanced by a particle lens

Abstract: In this work, a Graphene Oxide (GO) nano-sheet and SiO2 micro-bead hybrid system based on a frozen matrix was investigated for its enhanced optical nonlinear performance. A frozen matrix is a novel approach that hosts the optical nonlinear nano-particles, which combines the strengths from both liquid and solid phase systems for high performance photonic applications. SiO2 micro-beads were used to induce a local field enhancement effect that improved the optical nonlinearity of GO nano-sheets. The nonlinear performance of the hybrid system is several orders higher than the existing GO nano-sheet liquid dispersion. In addition, this frozen matrix and the local field enhancement effect are two facile and versatile methods that can be applied to many types of nano-particle dispersions.

Tunable optical nonlinearity of silicon nanoparticles in solid state organic matrix

Abstract: In this paper, a novel approach to fabricate a hybrid solid state system with both tunable nonlinearity and self-repairing property is studied. The optical nonlinear properties of a silicon nanoparticles system based on gel wax matrix were experimentally investigated. Tunable optical nonlinearities from optical limiting to saturable absorption were achieved by simply changing the concentration of nanoparticles inside the matrix. This approach opens a route for a low cost, one-step-synthesis nonlinear system being highly compatible with silicon optoelectronic circuits. This hybrid system also demonstrates the self-repairing property after excess exposure to laser irradiation.

Improved optical limiting performance of laser-ablation-generated metal nanoparticles due to silica-microsphere-induced local field enhancement

Abstract: For practical application, optical limiting materials must exhibit a fast response and a low threshold in order to be used for the protection of the human eye and electro-optical sensors against intense light. Many nanomaterials have been found to exhibit optical limiting properties. Laser ablation offers the possibility of fabricating nanoparticles from a wide range of target materials. For practical use of these materials, their optical limiting performance, including optical limiting threshold and the ability to efficiently attenuate high intensity light, needs to be improved. In this paper, we fabricate nanoparticles of different metals by laser ablation in liquid. We study the optical nonlinear properties of the laser-generated nanoparticle dispersion. Silica microspheres are used to enhance the optical limiting performance of the nanoparticle dispersion. The change in the optical nonlinear properties of the laser-generated nanoparticle dispersion caused by silica microspheres is studied. It is found that the incident laser beam is locally focused by the microspheres, leading to an increased optical nonlinearity of the nanoparticle dispersion.

Direct Laser Microperforation of Bioresponsive Surface-Patterned Films with Through-Hole Arrays for Vascular Tissue-Engineering Application

Abstract: Tissue architecture plays critical roles in the physiological functions of blood vessels. Surface-patterned films are promising to replicate cellular alignment as in the native vessels. However, for vascular tissue engineering (TE) applications, the current surface-patterned films lack structural support for the myoendothelial communications between tunica media and intima. Herein, we report the development of direct microperforation using a femtosecond laser on surface-patterned films for the native-like architecture reconstruction of blood vessels. Poly(e-caprolactone) (PCL) thin films were surface-patterned with anisotropic microridges/grooves. Direct femtosecond laser ablation further resulted in microscale through-holes for the PCL films, without invasive thermal damage to the ridges/grooves on the nonprocessed surface. Laser fluence and pulse number were observed to significantly influence the microperforation on both hole quality and dimension. The PCL films after direct femtosecond laser microperf...

Effect of pulse duration on heat transfer and solidification development in laser-melt magnesium alloy

Abstract: Compared to CW CO2 laser, Nd:YAG pulse laser is more suitable for some material processing due to higher absorptivity. However, surface ripples and microstructure inhomogeneities are main disadvantages during pulse laser melting on materials. Experiments were carried out to examine how laser melting influences surface topography and microstructure development of AZ91D Mg alloy. The laser-melt surface was characterized using Talysurf profiler, optical microscope and scanning electron microscope. Temperature distribution of molten pool was calculated from heat flow model to understand how heat transfer and fluid flow influence kinetics of rapid solidification under non-equilibrium conditions. The results implicate solidification behavior on microstructure evolution of laser-melt materials. At optimized parameters, thermally driven Marangoni flow became uniform, resulting in low height of ripples on top surface and less discrete bands in cross-sectional microstructure simultaneously, thereby improving homogeneity of microstructure in the molten pool.

Quantification of a cardiac biomarker in human serum using extraordinary optical transmission (EOT).

Abstract: Nanoimprinting lithography (NIL) is a manufacturing process that can produce macroscale surface areas with nanoscale features. In this paper, this technique is used to solve three fundamental issues for the application of localized surface plasmonic resonance (LSPR) in practical clinical measurements: assay sensitivity, chip-to-chip variance, and the ability to perform assays in human serum. Using NIL, arrays of 140 nm square features were fabricated on a sensing area of 1.5 mm x 1.5 mm with low cost. The high reproducibility of NIL allowed for the use of a one-chip, one-measurement approach with 12 individually manufactured surfaces with minimal chip-to-chip variations. To better approximate a real world setting, all chips were modified with a biocompatible, multi-component monolayer and inter-chip variability was assessed by measuring a bioanalyte standard (2.5−75 ng/ml) in the presence of a complex biofluid, human serum. In this setting, nanoimprinted LSPR chips were able to provide sufficient characteristics for a ‘low-tech’ approach to laboratory-based bioanalyte measurement, including: 1) sufficient size to interface with a common laboratory light source and detector without the need for a microscope, 2) high sensitivity in serum with a cardiac troponin limit of detection of 0.55 ng/ml, and 3) very low variability in chip manufacturing to produce a figure of merit (FOM) of 10.5. These findings drive LSPR closer to technical comparability with ELISA-based assays while preserving the unique particularities of a LSPR based sensor, suitability for multiplexing and miniaturization, and point-of-care detections.

Tissue scaffold device and method for fabricating thereof

Abstract: The invention relates to a tissue scaffold device and a method for fabricating the tissue scaffold device. The tissue scaffold device comprises a porous core including a plurality of fibres and an outer portion at least substantially surrounding the porous core, wherein the outer portion includes a plurality of pores elongated along a longitudinal axis of the tissue scaffold device. The tissue scaffold device is preferably a tendon scaffold, and the fibres preferably comprise collagen and poly(e-caprolactone) (PCL), with or without incorporation of hydroxyapatite nanoparticles.