Near-field Light Research Articles

Criterion to determine the wave vector range of heterodyne near-field exposure time-dependent spectrum.

Recently, image methods for measuring dynamics of nanoparticles have garnered attention; however, the low-speed frame rate of normal image sensors limits their application. Applying a low-speed detector can extract fast dynamic information by the method of an exposure time-dependent spectrum, whereas its accuracy is too sensitive to the wave vector range selection. In this paper, we present a criterion to determine the wave vector range for the image method of heterodyne near-field light scattering, where the hologram of the particles is analyzed to extract the particle dynamics. A normalized instrument factor ratio 𝓇(q) is defined, and the accuracy of results can be guaranteed when the upper limit qup is selected at the maximum of 𝓇(qup)=1, and the lower limit qlow is selected according to the optimal goodness of fit R2. The experimental results verify the effectiveness of the proposed criterion. Since most image methods for nanoparticle characterizing are related to the wave vector range selection, it is believed that the idea of this criterion can be extended generally.

Localized photonic nanojet based sensing platform for highly efficient signal amplification and quantitative biosensing

Light-analyte interaction systems are key elements of novel near-field optics based sensing techniques used for highly-sensitive detection of various kinds of targets. However, it is still a great challenge to achieve quantitative analysis of the targets using these sensing techniques, since critical difficulties exist on how to efficiently and precisely introduce the analytes into the desired location of the near-field light focusing, and quantitatively measure the enhanced optical signal reliably. In this work, we present for the first time a localized photonic nanojet (L-PNJ) based sensing platform which provides a strategy to achieve quantitative biosensing via utilizing a unique light-analyte interaction system. We demonstrate that individual fluorescent microsphere of different sizes can be readily introduced to the light-analyte interaction system with loading efficiency more than 70%, and generates reproducible enhanced fluorescence signals with standard deviation less than 7.5%. We employ this sensing platform for fluorescent-bead-based biotin concentration analysis, achieving the improvement on the detection sensitivity and limit of detection, opening the door for highly sensitive and quantitative biosensing. This L-PNJ based sensing platform is promising for development of next-generation on-chip signal amplification and quantitative detection systems.

Construction of Laterally Asymmetric Heterojunctions with Sub‐Micrometer Resolution by Hierarchical Self‐Assembly of Polythiophene Nanofibers

Polymeric semiconductors are crucial candidates for the construction of next-generation flexible and printable electronic devices. By virtue of the successful preparation of monodispersed colloidal solution in orthogonal solvent, poly(3-hexylthiophene) (P3HT) nanofibers are developed into versatile building blocks for nanoelectronics and their compatibilities are verified with photolithographic lift-off technology. Then, the joint efforts from both the bottom-up hierarchical self-assembly and top-down self-alignment technology have led to the realization of lateral asymmetric heterojunctions with resolution better than 1µm. As a result, planar photovoltaic devices incorporating N,N'-dioctyl-3,4,9,10-perylenedicarboximide and P3HT supramolecular nanowires as active components are constructed with the cathode-to-anode distance being tuned from ≈0.1 to 1-2µm. Based on such a novel device configuration, an interesting phenomenon of channel-length-dependent photovoltaic efficiency is observed for the first time, strongly suggesting the impact of near-field light intensity on the performance of nanophotonic devices.

Surface Defect Detection on Nuclear Power Plant Components Based on Photometric Stereo under Near-Field LED Light

To improve the visual inspection of nuclear power plant components, this study introduces the technology of three-dimensional reconstruction framework based on photo metric stereo under near-field LED lighting. An iterative algorithm is proposed to estimate the K value of different light sources and the light6 intensities for various image pixels. Combined with the calculation method of the spatial position of the light source and the detected surface points, the light intensity and light direction of different points on the detected surface are estimated under the illumination of near-field LED point light source. A surface defect detection system is designed based on this technology, and it is verified by experiments on surface damage samples and actual nuclear power equipment. The results show that this system can obtain three-dimensional surface data, and for scratch-type defects, it can further achieve accurate depth measurement. Therefore, it can effectively improve the detection ability of surface defects.

Experimental investigation of optically controlled topological transition in bismuth-mica structure

The hyperbolic materials are strongly anisotropic media with a permittivity/permeability tensor having diagonal components of different sign. They combine the properties of dielectric and metal-like media and are described with hyperbolic isofrequency surfaces in wave-vector space. Such media may support unusual effects like negative refraction, near-field radiation enhancement and nanoscale light confinement. They were demonstrated mainly for microwave and infrared frequency ranges on the basis of metamaterials and natural anisotropic materials correspondingly. For the terahertz region, the tunable hyperbolic media were demonstrated only theoretically. This paper is dedicated to the first experimental demonstration of an optically tunable terahertz hyperbolic medium in 0.2–1.0 THz frequency range. The negative phase shift of a THz wave transmitted through the structure consisting of 40 nm (in relation to THz wave transmitted through substrate) to 120 nm bismuth film (in relation to both THz waves transmitted through substrate and air) on 21 µm mica substrate is shown. The optical switching of topological transition between elliptic and hyperbolic isofrequency contours is demonstrated for the effective structure consisting of 40 nm Bi on mica. For the case of 120 nm Bi on mica, the effective permittivity is only hyperbolic in the studied range. It is shown that the in-plane component of the effective permittivity tensor may be positive or negative depending on the frequency of THz radiation and continuous-wave optical pumping power (with a wavelength of 980 nm), while the orthogonal one is always positive. The proposed optically tunable structure may be useful for application in various fields of the modern terahertz photonics.

Light–Matter Interaction Enhancement in Anisotropic 2D Black Phosphorus via Polarization-Tailoring Nano-Optics

Black phosphorus (bP), a two-dimensional (2D) layered material, has shown great potential for infrared (IR) optoelectronics owing to the narrow and direct bandgap it exhibits when in multilayer form. However, its thinness and optical anisotropy lead to weak light absorption, which limits the performance of bP-based photodetectors. In this work, we explore plasmonic nanoantennas, optical cavities, and their hybrids that can be integrated with multilayer bP to enhance its light absorption. This is achieved by near-field light intensity enhancement and polarization conversion. In addition, we demonstrate that these nanostructures can boost the spontaneous emission from bP. Light absorption enhancements of up to 185 and 16 times are obtained for linearly polarized and unpolarized IR light, respectively, in comparison with a commonly used device architecture (bP on SiO2/Si). Moreover, IR light emission enhancements of up to 18 times are achieved. The optical nanostructures presented here can be exploited for enhancing the detectivity of photodetectors and electroluminescence efficiency of light-emitting diodes based on bP and other 2D materials.

Assessing Effects of Near-Field Synergistic Light Absorption on Ordered Inorganic Phototropic Growth.

We report herein that synergistic light absorption in the optical near-field enables nanoscale self-organization during inorganic phototropic growth. Se-Te was grown electrochemically under illumination from an incoherent, unstructured light source in geometrically constrained, wavelength scale areas. Despite the limited dimensions, with as few as two discrete features produced in a single sub-micron dimension, the deposit morphology exhibited defined order and anisotropy. Computer modeling analysis of light absorption in simulated structures revealed a synergy wherein light capture in a nanoscale feature was enhanced by the presence of additional adjacent features, with the synergistic effect originating predominantly from nearest neighbor contributions. Modeling moreover indicated that synergistic absorption is produced by scattering of the incident illumination by individual nanoscale features, leading to a local increase in the near-field intensity and consequently increasing the absorption in neighboring features. The interplay between these optical processes establishes the basis for spontaneous order generation via inorganic phototropic growth.

Optical properties and annealing effects of planar waveguides on fluoride lead silicate glass formed by proton and helium-ion implantation

The optical planar waveguides were fabricated by proton implantation with an energy of 400 keV and a dose of 8 × 1016 ions / cm2 or 400-keV helium-ion implantation with a fluence of 6 × 1016 ions / cm2 in the fluoride lead silicate glass. The morphologies were studied by a Zeiss microscope to estimate the thickness of the waveguides. The annealing effects on the fluoride lead silicate glass waveguides were investigated by 60 min annealing cycles at different temperatures ranging from 260°C to 310°C in air atmosphere. The dark-mode spectra and corresponding effective refractive indices before and after the thermal treatments were measured by the prism coupling system. The Stopping and Range of Ions in Matter 2013 code was used to simulate the irradiation process and calculate the energy losses. The refractive index distributions were reconstructed by the reflectivity calculation method. The near-field light intensity profiles of the proton and helium-ion implanted fluoride lead silicate glass waveguides were measured by the end-face coupling system. The comparison of optical properties between the proton-implanted waveguide and helium-ion implanted one was carried out. The experimental results show that the helium-ion implantation is more suitable for the fabrication of the fluoride lead silicate glass optical waveguides and the He + -implanted waveguide has better optical propagation performances.

Enhanced Raman intensity in ZnS planar and channel waveguide structures via carbon ion implantation

Planar and channel waveguides in ZnS single crystal are fabricated by 6.0 MeV C ion implantation with fluences of 5 × 1014 and 1 × 1015 ion/cm2 at room temperature. The optical modes for the planar waveguides are measured by using a prism coupler by the well-known m-line method. The near-field light intensity profiles for the planar and channel waveguides are measured by the end-face coupling setup at 633 nm and 1539 nm. The reflectivity calculation method and the finite difference beam propagation method are used to reconstruct the refractive index profile of the planar waveguides and near-field intensity distribution of planar and channel waveguides. Raman images obtained with a 532-nm laser are collected to evaluate the damage to the ZnS crystal and waveguide layers.

Strong Near-Field Light–Matter Interaction in Plasmon-Resonant Tip-Enhanced Raman Scattering in Indium Nitride

We report a detailed study of the strong near-field Raman scattering enhancement, which takes place in tip-enhanced Raman scattering (TERS) in indium nitride. In addition to the well-known first-or...

Recent progress and challenges on two-dimensional material photodetectors from the perspective of advanced characterization technologies

Atomically thin two-dimensional (2D) materials exhibit enormous potential in photodetectors because of novel and extraordinary properties, such as passivated surfaces, tunable bandgaps, and high mobility. High-performance photodetectors based on 2D materials have been fabricated for broadband, position, polarization-sensitive detection, and large-area array imaging. However, the current performance of 2D material photodetectors is not outstanding enough, including response speed, detectivity, and so forth. The way to further promote the development of 2D material photodetectors and their corresponding practical applications is still a tremendous challenge. In this article, these issues of 2D material photodetectors are analyzed and expected to be solved by combining micro-nano characterization technologies. The inherent physical properties of 2D materials and photodetectors can be accurately characterized by Raman spectroscopy, transmission electron microscopy (TEM), and scattering scanning near-field optical microscope (s-SNOM). In particular, the precise probe of lattice defects, doping concentration, and near-field light absorption characteristics can promote the researches of low-noise and high-responsivity photodetectors. Scanning photocurrent microscope (SPCM) can show the overall spatial distribution of photocurrent and analyze the mechanism of photocurrent. Photoluminescence (PL) spectroscopy and Kelvin probe force microscope (KPFM) can characterize the material bandgap, work function distribution and interlayer coupling characteristics, making it possible to design high-performance photodetectors through energy band engineering. These advanced characterization techniques cover the entire process from material growth, to device preparation, and to performance analysis, and systematically reveal the development status of 2D material photodetectors. Finally, the prospects and challenges are discussed to promote the application of 2D material photodetectors.

Simulation on near-field light on recording medium generated by semiconductor ring resonator with metal nano-antenna for heat-assisted magnetic recording

Heat-assisted magnetic recording (HAMR) is a promising technology for achieving more than 10 Tbit/inch2 recording density. A near-field transducer (NFT), which forms a small light spot on a recording medium, is necessary in HAMR. However, the heat generated by the NFT would melt the NFT itself. To solve this problem, the authors have proposed a novel device, in which a metal nano-antenna is attached to a semiconductor ring resonator. In this paper, the near-field light generated by this device was analyzed through a numerical simulation based on a 3-dimensional model including the recording medium to optimize the structure of the device. It was found that how to excite a desired eigenmode selectively among some eigenmodes is important to make the device effective. A light spot with a diameter of about 25 nm, which corresponds to the recording density of 1 Tb/inch2, was obtained on the surface of the recording medium. It was also found that the design parameters of the device must be optimized considering the recording medium.

Strong Interaction of Slow Electrons with Near-Field Light Visited from First Principles.

Strong interaction between light and matter waves, such as electron beams in electron microscopes, has recently emerged as a new tool for manipulating the electron wave packets. Here, we systematically investigate electron-light interactions from first principles. We show that enhanced coupling can be achieved for systems involving slow electron wave packets interacting with plasmonic nanoparticles, due to simultaneous classical recoil and quantum mechanical photon absorption and emission processes. For slow electrons with longitudinal broadenings longer than the dimensions of nanoparticles, phase matching between slow electrons and plasmonic oscillations is manifested as an additional degree of freedom to control the strength of coupling. Our findings pave the way toward a systematic and realistic understanding of electron-light interactions beyond adiabatic approximations, and lay the ground for the realization of matter-wave interferometry and boson-sampling devices involving light and matter waves.

64‐2: Metrology of Non‐Planar Light Sources Using Near‐Field Goniometric Measurement Method

In this paper we study the metrology issues of non‐planar light sources (NPLSs). We use near‐field (NF) goniometric measurement method to characterize the NPLSs. By using the NF method, we obtain the luminance image, the intensity, the spectra and the color of the source as a function of the ray angle, i.e., the zenith and azimuth angles in spherical coordinate system. The NF light rays are used to obtain the characteristics of the light source at far‐fields by post processing. The results of the NPLS metrology and the features of the NF goniometric measurement system are reported.

High Performance and Efficiency Resonant Photo-Effect-Transistor by Near-Field Nano-Strip-Controlled Organic Light Emitting Diode Gate.

Phototriggered devices have attracted attention due to their exceptional characteristics, advanced multifunctionalities and unprecedented applications in optoelectronic systems. Here, we report a pioneer structural device, a resonant photoeffect-transistor (RPET) with a functionalized nanowire (NW) charge transport channel, modulated by a near-field nanostrip organic light emitting diode (OLED) and controlled by a gate bias to realize exceptional photoelectric properties. The RPET presents high-quality nanowire channel characteristics due to tunable optical cavities manifesting strong standing wave resonance under controlled light emission. To enhance performance, methodical analyses were carried out to determine the effects of the structural design, electric field distribution and charge carrier generation on photoresponsivity when light traverses a single or multiple nanoslit masks. The developed RPET yields stable photocurrents in the 105 range and generates current on/off ratios upward of 106 under the influence of intense electromagnetic distribution, effectively lending itself to promising opportunities in fully integrated optoelectronic devices.

Laser-induced periodic surface structures: Arbitrary angles of incidence and polarization states

We demonstrate that the finite-difference time-domain (FDTD) method can be used to study the formation of laser-induced periodic surface structures (LIPSSs) under oblique incidence and arbitrary polarization states. The inhomogeneous energy absorption below a rough surface at oblique incident angle is studied by the FDTD method and compared to the analytical efficacy theory developed by Sipe et al. [Phys. Rev. B 27, 1141 (1983)10.1103/PhysRevB.27.1141]. The two approaches show excellent agreement. The surface topographies of both low-spatial-frequency LIPSSs (LSFLs) and high-spatial-frequency LIPSSs (HSFLs) at oblique incidence and various polarization states (linear, circular, radial, and azimuthal) are simulated by taking into account topography-driven interpulse feedback effects. For s- and mixed s- and p-polarized beams at large incident angles, the simulated LSFLs show orientations that are neither perpendicular nor parallel to the laser polarization. Their physical origin is explained by a nonzero angle between the in-plane wave vector of the incident light and the scattered light. By using circularly-polarized beams, the simulated surface topographies are further shown to be in excellent agreement with the triangular LSFLs and the fine-dot nanoscaled structures reported in the literature. In addition, the simulation of HSFLs suggests that their periods have almost no dependence on the incident angle nor the polarization angle, while their surface topographies resemble that of blazed gratings at large incident angles for p-polarized and mixed s- and p-polarized beams. The origin is explained by the appearance of asymmetry in the scattered near-field light. The extension to oblique incidence and arbitrary polarization states demonstrates that the FDTD approach on LIPSSs is a highly versatile and powerful technique which has the potential to be one of the foundations for a complete modeling and understanding of LIPSSs under various irradiation conditions.

Ultra-High-Responsivity Vertical Nanowire-based Phototransistor under Standing-Wave Plasmon Mode Interaction Induced by Near-Field Circular OLED.

High-responsivity photodevices are strongly desired for various demanding applications, such as optical communications, logic circuits, and sensors. The use of quantum and photon confinement has enabled a true revolution in the development of high-performance devices. Unfortunately, many practical optoelectronic devices exhibit intermediate sizes where resonant enhancement effects seem to be insignificant. Here we design and fabricate an ultra-high-responsivity organic-light-emitting-diode-induced nanowire resonance phototransistor (ONRPT) based on standing-wave resonance in the nanoscale cavity, subjected to a near-field light. Observations of the ONRPT in standing-wave resonance mode indicate a >104 enhancement in the on/off ratio and a six times higher subthreshold slope when compared with the ONRPT in non-resonance mode. The ONRPT, which leads itself to outstanding electrical and favorably stable performance, opens up a plethora of opportunities for high-efficiency energy devices and allows for nanowire applications in the solar cell, piezo-photonic detectors, and optical modulators.

Optical modulation of repaired damage site on fused silica produced by CO2 laser rapid ablation mitigation**Project supported by the National Natural Science Foundation of China (Grant Nos. 51775147 and 51705105), the Science Challenge Project of China (Grant No. TZ2016006-0503-01), the Young Elite Scientists Sponsorship Program by CAST (Grant No. 2018QNRC001), the China Postdoctoral Science Foundation funded project (Grant Nos. 2018T110288

CO2 laser rapid ablation mitigation (RAM) of fused silica has been used in high-power laser systems owing to its advantages of high efficiency, and ease of implementing batch and automated repairing. In order to study the effect of repaired morphology of RAM on laser modulation and to improve laser damage threshold of optics, an finite element method (FEM) mathematical model of 351 nm laser irradiating fused silica optics is developed based on Maxwell electromagnetic field equations, to explore the 3D near-field light intensity distribution inside optics with repaired site on its surface. The influences of the cone angle and the size of the repaired site on incident laser modulation are studied as well. The results have shown that for the repaired site with a cone angle of 73.3°, the light intensity distribution has obvious three-dimensional characteristics. The relative light intensity on z-section has a circularly distribution, and the radius of the annular intensification zone increases with the decrease of z. While the distribution of maximum relative light intensity on y-section is parabolical with the increase of y. As the cone angle of the repaired site decreases, the effect of the repaired surface on light modulation becomes stronger, leading to a weak resistance to laser damage. Moreover, the large size repaired site would also reduce the laser damage threshold. Therefore, a repaired site with a larger cone angle and smaller size is preferred in practical CO2 laser repairing of surface damage. This work will provide theoretical guidance for the design of repaired surface topography, as well as the improvement of RAM process.

曲面近场发光二极管阵列照度均匀性分析与设计

曲面近场发光二极管阵列照度均匀性分析与设计

Derivation and Experimental Verification of the Near-field 2D and 3D Optical Intensities From a Finite-size Light Emitting Diode (LED)

We derive the near-field light intensity distributions of an inorganic LED on its surface and in volumetric space. Our closed-form solution for 3D intensity distribution for a finite-size LED is consistent with Lambert's Cosine Law, which provides the 3D intensity distribution for an infinitesimal, flat light source. We also derive the formula for the 2D intensity distribution on a diode surface showing its similarity to a Gaussian function, which is typically used to approximate the surface light intensity profile for an LED and a laser diode. Our 2D intensity distribution function produces light propagation similar to the Gaussian beam propagation in space. However, unlike the Gaussian approximation, our formula invariably produces this behavior without assuming the refractive index inside the diode follows a quadratic function of the transverse spatial domains. Our 2D and 3D spatial intensity formulas in near-field for LEDs offer a unique way to calculate the peak intensity that occurs at the center of the flat LED source. We demonstrate, as expected, that the peak intensity increases with the size of the LED source as well as the brightness of each radiative electron-hole pair, which is a function of the drive current and quantum efficiency of the LED.