Study on the imaging characteristics of far-field superlens

The optical transfer function of the far-field superlens imaging system is established in this thesis to make it easy to describe the corresponding relation between the far-field angular spectrum and the near-field object superresolution information. We utilized the established optical transfer function to make detailed research on the imaging characteristics of the far-field superresolution, also reconstruct the near-field nano-information through the far-field angular spectrum, which proves that the resolution of the far-field superlens with structure coupled with metal grating can reach 50 nm, and provides a helpful reference for the study of the new optical microscope imaging of superresolution.     

Hybrid near-field optical memory and photofabrication in dye-doped polymer film

A hybrid near-field fluorescence microscopy, which combines near-field scanning optical microscopy and photon scanning tunneling microscopy, is demonstrated for nanoscale optical memory and photofabrication on spin-coated dye-doped polymer films. Storage capacity and readout signal-to-noise ratio with near-field one-photon and two-photon excitations are studied.     

Quantitative assessment of touch-screen panel by nondestructive inspection with three-dimensional real-time display optical coherence tomography

We investigated the use of optical coherence tomography (OCT) to measure several materials immersed in optical adhesives. The effects of variations in the concentration, physical characteristics, and thickness of the materials were studied, and these parameters were found to significantly affect the OCT measurement. The materials were selected for their distinct spectral properties in the infrared region. To ensure reliability, we acquired images using a scanning electron microscope after performing the semiconductor production process. We verified the feasibility of the application of OCT for defect inspection and product verification of touch-screen panels.     

远场光钳与近场光钳的发展

以经典光学为基础的光钳技术(又称"光镊")在生物、物理和化学等领域得到了广泛的发展和应用,但是该技术受到高倍显微物镜的尺寸和光学衍射极限等多种因素的制约,从而限制了其进一步发展。而远场光纤光钳和近场光钳技术,从不同方面克服了传统光钳的局限。回顾了传统光钳、远场光纤光钳和近场光钳的发展,着重讨论了各种方法的工作原理、实验方法和技术性能,对这几种光钳技术进行了深入地总结和细致地比较。     

Surface structure monitoring with plastic optical fiber

A sensor was designed using a plastic optical fiber to study the potential of detecting structural deformities and corrosion of metallic surfaces, in particular for applications in constricted areas such as pipes. The principle of the sensor is based on the collection of scattered light reflected by the surface imperfections. Several types of metallic materials in various surface profiles and stages of corrosion have been studied. The sensor was able to determine the position of ridges on the surface and corroded regions in all cases evaluated in the study. A sensitivity of 100 mV/mm was detectable for proximity and a vertical resolution of 1 mm has been measured.     

Near-field and far-field modeling of scattered surface waves. Application to the apertureless scanning near-field optical microscopy

The detection of surface waves through scanning near-field optical microscopy (SNOM) is a promising technique for thermal measurements at very small scales. Recent studies have shown that electromagnetic waves, in the vicinity of a scattering structure such as an atomic force microscopy (AFM) tip, can be scattered from near to far-field and thus detected. In the present work, a model based on the finite difference time domain (FDTD) method and the near-field to far-field (NFTFF) transformation for electromagnetic waves propagation is presented. This model has been validated by studying the electromagnetic field of a dipole in vacuum and close to a dielectric substrate. Then simulations for a tetrahedral tip close to an interface are presented and discussed.     

Resonant Raman scattering of optical phonons in self-assembled quantum dots

We have investigated the carrier relaxation mechanism in InGaAs/GaAs quantum dots by photoluminescence excitation (PLE) spectroscopy. Near-field scanning optical microscope successfully shows that a PLE resonance at a relaxation energy of 36 meV can be seen in all single-dot luminescence spectra, and thus can be attributed to resonant Raman scattering by a GaAs LO phonon to the excitonic ground state. In addition, a number of sharp resonances observed in single-dot PLE spectra can be identified as resonant Raman features due to localized phonons, which are observed in the conventional Raman spectrum. The results reveal the mechanism for the efficient relaxation of carriers observed in self-assembled quantum dots: the carriers can relax within the continuum states, and make transitions to the excitonic ground state by phonon emission.     

Direct observation of variations of optical properties in single quantum dots by using time-resolved near-field scanning optical microscope

We study the variations of optical properties of self-assembled In_0.5Ga_0.5As single quantum dots (QDs) in the spatial and time domains by combining a near-field scanning optical microscope with an ultrafast pulsed laser. Through the examinations of several tens of QDs, we find that the variations of photoluminescence (PL) intensity strongly depend on the condition of the initial carrier creation. The differences in quantum efficiency and those in the carrier flow rate into QDs cause the large distribution of PL intensity when the carriers are excited in the barrier layers. From the results of time-resolved PL decay measurements, we find that there are two types of QDs exhibiting quite different PL decay profiles.     

THz near-field optical imaging by a local source

A new THz imaging system based on a local illumination by a near-field source is presented. Model object is imaged, and sub-wavelength spatial resolution is demonstrated for the first time to our knowledge with this configuration. The contrast and the resolution are confirmed by a theoretical study based on the diffraction in near-field zone.     

A new positioning approach of fiber probe for near-field scanning optical microscope

A fiber probe-based positioning scan approach was established, whose precision can reach as high as 0.8 μm. And a set of modified microscope system was designed utilizing this approach, in which the scanning probe microscope (SPM) combined with an optical microscope was manipulated. The optical microscope and scanning probe can conveniently be switched through a switch panel. The observation period of samples can significantly be shortened. And more reliable images can be provided using this approach. Our design can effectively solve the inherent disadvantages of SPM technology, which makes SPM scan and image more reliably, conveniently, safely and rapidly.     

Inspection of orientation of micro fibres in dried wood by a diffractive optical element

Orientation of micro fibres in dried wood was investigated by using diffractive optical element (DOE)-based sensor. Correlation between the visibility of the images of the DOE sensor and small-angle X-ray diffraction responses was observed.     

有孔探针近场拉曼光谱和成像技术进展

基于有孔探针SNOM的近场拉曼光谱和成像技术的出现使得拉曼光谱的分辨率突破了光学衍射极限,从而提供了一个有力的工具对样品亚波长尺度之下的化学信息进行表征。文章讨论了探针性质对实现近场拉曼光谱的影响,并全面地介绍了有孔探针近场拉曼光谱发展十余年来在纳米尺度化学分辨成像、液-液界面性质研究、微观层面解释SERS增强机理、图像化反映SERS热点分布等诸多领域的研究进展。     

Light extraction from a light emitting diode with photonic structure in the surface layer investigated by NSOM

We present a light emitting diode with a two-dimensional photonic crystal structure prepared by interference lithography at the light emitting diode surface. The emission maximum is at 850 nm. The two-dimensional photonic crystal structure enhanced the light extraction efficiency by a factor of 1.39. The photonic crystal light emitting diode surface morphology was analyzed by atomic force microscopy. The enhanced extraction efficiency of the photonic crystal diode was documented from L(I) dependencies and was confirmed by near-field studies.     

Near-field optical microscopy of nonlinear susceptibilities

Local probing of second-order susceptibilities with a near-field optical microscope is demonstrated for the first time. Using an uncoated fiber tip as a light source, near-field images of a surface of y-cut LiNbO₃ crystal and of a multilayer Langmuir–Blodgett film of 2-docosylamino-5-nitropyridine are obtained at the fundamental pump and second harmonic wavelengths while simultaneously recording surface topography. It is shown that optical second-harmonic images for different polarizations of the pump light reflect the difference in magnitude of the corresponding components of the second-order susceptibility tensor. Various degrees of correlation in contrast of optical (fundamental and second harmonic) and topographical images are observed and discussed.     

Nano-optical imaging and spectroscopy of order,phases, and domains in complex solids

The structure of our material world is characterized by a large hierarchy of length scales that determines material properties and functions. Increasing spatial resolution in optical imaging and spectroscopy has been a long standing desire, to provide access, in particular, to mesoscopic phenomena associated with phase separation, order, and intrinsic and extrinsic structural inhomogeneities. A general concept for the combination of optical spectroscopy with scanning probe microscopy emerged recently, extending the spatial resolution of optical imaging far beyond the diffraction limit. The optical antenna properties of a scanning probe tip and the local near-field coupling between its apex and a sample provide few-nanometer optical spatial resolution. With imaging mechanisms largely independent of wavelength, this concept is compatible with essentially any form of optical spectroscopy, including nonlinear and ultrafast techniques, over a wide frequency range from the terahertz to the extreme ultraviolet. The past 10 years have seen a rapid development of this nano-optical imaging technique, known as tip-enhanced or scattering-scanning near-field optical microscopy (s-SNOM). Its applicability has been demonstrated for the nano-scale investigation of a wide range of materials including biomolecular, polymer, plasmonic, semiconductor, and dielectric systems.

We provide a general review of the development, fundamental imaging mechanisms, and different implementations of s-SNOM, and discuss its potential for providing nanoscale spectroscopic including femtosecond spatio-temporal information. We discuss possible near-field spectroscopic implementations, with contrast based on the metallic infrared Drude response, nano-scale impedance, infrared and Raman vibrational spectroscopy, phonon Raman nano-crystallography, and nonlinear optics to identify nanoscale phase separation (PS), strain, and ferroic order. With regard to applications, we focus on correlated and low-dimensional materials as examples that benefit, in particular, from the unique applicability of s-SNOM under variable and cryogenic temperatures, nearly arbitrary atmospheric conditions, controlled sample strain, and large electric and magnetic fields and currents. For example, in transition metal oxides, topological insulators, and graphene, unusual electronic, optical, magnetic, or mechanical properties emerge, such as colossal magneto-resistance (CMR), metal–insulator transitions (MITs), high-T _C superconductivity, multiferroicity, and plasmon and phonon polaritons, with associated rich phase diagrams that are typically very sensitive to the above conditions. The interaction of charge, spin, orbital, and lattice degrees of freedom in correlated electron materials leads to frustration and degenerate ground states, with spatial PS over many orders of length scale. We discuss how the optical near-field response in s-SNOM allows for the systematic real space probing of multiple order parameters simultaneously under a wide range of internal and external stimuli (strain, magnetic field, photo-doping, etc.) by coupling directly to electronic, spin, phonon, optical, and polariton resonances in materials. In conclusion, we provide a perspective on the future extension of s-SNOM for multi-modal imaging with simultaneous nanometer spatial and femtosecond temporal resolution.     

Carrier-diffusion-limited remote optical addressing of single quantum dots

We present a scheme for remotely addressing single quantum dots (QDs) by means of near-field optical microscopy that simply makes use of the polarization of light. A structure containing self-assembled CdTe QDs is covered with a thin metal film presenting sub-wavelength holes. When the optical tip is positioned some distance away from a hole, surface plasmons in the metal coating are generated which, by turning the polarization plane of the excitation light, transfer the excitation towards a chosen hole and induce emission from the underlying dots. In addition, our procedure gives valuable insight into the diffusion of photo-excited carriers in the QD plane that can put limits to the addressing scheme.     

光偶极天线的远场方向性研究

用时域有限差分方法模拟了两种光偶极天线模型的场分布,研究了光偶极天线的远场辐射特性随其长度增加而变化的规律以及影响其远场方向性的因素,发现光偶极天线的远场方向性随其长度增加而变化的规律类似于经典对称振子天线的相应规律.但高阶局域表面等离激元模式的存在使得光偶极天线的远场辐射图更快地出现了旁瓣.这些发现对于提高光天线的性能具有重要意义. 关键词： 光偶极天线 局域表面等离激元 金纳米粒子 远场方向性     

Near-field optical characterization of GaN and InxGa1−xN/GaN heterostructures grown on freestanding GaN substrates

Using near-field scanning optical microscopy (NSOM), we report the spatial distribution of photoluminescence (PL) intensity in III-nitride-based semiconductor layers grown on GaN substrates. Undoped GaN, In_0.11Ga_0.89N, and In_0.13Ga_0.87N/GaN multi-quantum wells (MQWs) were grown by metal organic chemical vapor deposition (MOCVD) on freestanding GaN substrates. Micro-Raman spectroscopy has been used to evaluate the crystalline properties of the GaN homoepitaxial layers. The variation of the PL intensity from the NSOM imaging indicates that the external PL efficiency fluctuates from 20% to 40% in the 200 nm InGaN single layer on freestanding GaN, whereas it fluctuates from 20% to 60% in InGaN/GaN MQWs. In the NSOM-PL images, bright island-like features are observed. After deconvolution with the spatial resolution of the NSOM, the size of these features is estimated to be in the range of 150–250 nm.     

Imaging quality analysis and evaluation of optical polarization imaging system with optical transfer matrix

An optical transfer matrix (OTM) is introduced and proposed to analyze the performance of optical polarization imaging systems. This 4 × 4 OTM describes the frequency transfer characteristics of the optical system for each Stokes parameter. It includes the transfer functions and the crosstalk functions. The transfer functions can be used to analyze the imaging quality of the system for each polarization component, while crosstalk functions indicate the polarization errors. We calculate the modulation transfer matrix as an example and numerically simulate the Stokes vector imaging for a polarization imaging system with a singlet and rotating polarization elements. The simulated imaging results show conformance with the analysis.     

Scanning Near-Field Optical Microscopy and Microspectroscopy of Green Fluorescent Protein in Intact Escherichia coli Bacteria

Scanning near-field optical microscopy (SNOM) yields high-resolution topographic and optical information and constitutes an important new technique for visualizing biological systems. By coupling a spectrograph to a near-field microscope, we have been able to perform microspectroscopic measurements with a spatial resolution greatly exceeding that of the conventional optical microscope. Here we present SNOM images of Escherichia coli bacteria expressing a mutant green fluorescent protein (GFP), an important reporter molecule in cell, developmental, and molecular biology. Near-field emission spectra confirm that the fluorescence detected by SNOM arises from bacterially expressed GFP molecules.