Search

The mid‐infrared with a characteristic wavelength of 3–20 μm is important for a wealth of technologies. In particular, mid‐infrared spectroscopy can reveal material composition and structure information by fingerprinting chemical bonds' infrared resonances. Despite these merits, state‐of‐the‐art mid‐infrared techniques are spatially limited above tens of micrometers due to the fundamental diffraction law. Herein, recent progress in the scanning probe nanoscale infrared characterization of biochemical materials and natural specimens beyond this spatial limitation is reviewed. By leveraging the strong tip–sample local interactions, scanning probe nano‐infrared methods probe nanoscale optical and mechanical responses to disclose material composition, heterogeneity, orientation, fine structure, and phase transitions at unprecedented length scales. These advances, therefore, revolutionize the understanding of a broad range of biochemical and natural materials and offer new material manipulation and engineering opportunities close to the ultimate length scales of fundamental physical, chemical, and biological processes. [ABSTRACT FROM AUTHOR]

Achieving subwavelength optical focusing is of great importance in nanophotonics. However, achieving focusing with both a small focal spot size and a large focal length remains elusive so far. Here, a large focal length planar focusing device is presented, utilizing highly oriented Dyakonov polaritons in hyperbolic metamaterial with periodic silver rings as the excitation source. Experimental results show that by controlling the size of the excitation sources, the focal length can reach 6 λ 0 (where λ 0 is the illumination wavelength), and the focal spot size can be reduced to λ 0 /10. This method provides new prospects for planar polariton optical applications. [ABSTRACT FROM AUTHOR]

Guided waves are the perfect carriers of electromagnetic signals in planar miniaturized devices due to their high localization and controlled propagation direction. However, it is still a challenge to control the polarization of propagating guided waves. In this work, the broadband polarization TE‐TM degeneracy of highly localized guided waves propagating along an all‐dielectric metasurface and a subwavelength chain of dielectric high‐index cylinders is discovered, both theoretically and experimentally. Using the discovered near‐field polarization degree of freedom, the polarization transformation for guided waves propagating along a subwavelength chain of dielectric cylinders at any frequency within the finite spectral range is demonstrated experimentally. Namely, the simplest planar near‐field polarization device – the quarter‐wave‐retardation (linear‐to‐circular) polarization transformer of guided waves is implemented. The results obtained discover the polarization degree of freedom for guided waves paving the way toward numerous applications in flat optics and planar photonics. [ABSTRACT FROM AUTHOR]

Multilayer core–shell microparticles with a liquid core and a polycomposite light-absorbing shell (microcapsules) are important components of modern bio- and medical technologies. Opening of the microcapsule shell and payload release can be realized by optical radiation. The photophoretic force is due to the radiation-stimulated thermal gradient and arises from the temperature inhomogeneity of the microparticle. Photophoretic forces, as well as radiation pressure forces, are inherently mechanical forces and can cause microcapsules to move during the opening cycle. We numerically simulate the microcapsule photophoretic motion when illuminated by an intense laser pulse. Numerical calculations of the temperature field in a spherical microcapsule are carried out using the finite element method, taking into account the auxiliary nanoparticles, which are randomly distributed around the capsule and serve to enhance the heating of the capsule under short pulse exposure. The spatial distribution of the absorbed optical power as well as the temporal dynamics of microcapsule heating depending of its size are investigated in detail. We show, for the first time to our knowledge, that under the joint action of light pressure and photophoretic forces, the microcapsule can move along the laser incidence direction both forward and backward at the distance of several tens of nanometers depending on the particle size and conditions of optical absorption. [ABSTRACT FROM AUTHOR]

The mid‐infrared with a characteristic wavelength of 3–20 μm is important for a wealth of technologies. In particular, mid‐infrared spectroscopy can reveal material composition and structure information by fingerprinting chemical bonds’ infrared resonances. Despite these merits, state‐of‐the‐art mid‐infrared techniques are spatially limited above tens of micrometers due to the fundamental diffraction law. Herein, recent progress in the scanning probe nanoscale infrared characterization of biochemical materials and natural specimens beyond this spatial limitation is reviewed. By leveraging the strong tip–sample local interactions, scanning probe nano‐infrared methods probe nanoscale optical and mechanical responses to disclose material composition, heterogeneity, orientation, fine structure, and phase transitions at unprecedented length scales. These advances, therefore, revolutionize the understanding of a broad range of biochemical and natural materials and offer new material manipulation and engineering opportunities close to the ultimate length scales of fundamental physical, chemical, and biological processes.

Chiral Weyl fermions with linear energy-momentum dispersion in the bulk accompanied by Fermi-arc states on the surfaces prompt a host of enticing optical effects. While new Weyl semimetal materials keep emerging, the available optical probes are limited. In particular, isolating bulk and surface electrodynamics in Weyl conductors remains a challenge. We devised an approach to the problem based on near-field photocurrent imaging at the nanoscale and applied this technique to a prototypical Weyl semimetal TaIrTe4 As a first step, we visualized nano-photocurrent patterns in real space and demonstrated their connection to bulk nonlinear conductivity tensors through extensive modeling augmented with density functional theory calculations. Notably, our nanoscale probe gives access to not only the in-plane but also the out-of-plane electric fields so that it is feasible to interrogate all allowed nonlinear tensors including those that remained dormant in conventional far-field optics. Surface- and bulk-related nonlinear contributions are distinguished through their "symmetry fingerprints" in the photocurrent maps. Robust photocurrents also appear at mirror-symmetry breaking edges of TaIrTe4 single crystals that we assign to nonlinear conductivity tensors forbidden in the bulk. Nano-photocurrent spectroscopy at the boundary reveals a strong resonance structure absent in the interior of the sample, providing evidence for elusive surface states.

The underlying physics behind an experimental observation often lacks a simple analytical description. This is especially the case for scanning probe microscopy techniques, where the interaction between the probe and the sample is nontrivial. Realistic modeling to include the exact details of the probe is widely acknowledged as a challenge. Due to various complexity constraints, the probe is often only approximated in a simplified geometry, leading to a source for modeling inconsistencies. On the other hand, a well-trained artificial neural network based on real data can grasp the hidden correlation between the signal and the sample properties, circumventing the explicit probe modeling process. In this work we show that, via a combination of model calculation and experimental data acquisition, a physics-infused hybrid neural network can predict the probe-sample interaction in the widely used scattering-type scanning near-field optical microscope. This hybrid network provides a long-sought solution for accurate extraction of material properties from tip-specific raw data. The methodology can be extended to other scanning probe microscopy techniques as well as other data-oriented physical problems in general.

Phonon polaritons (PhPs) provide new prospects for the development of next generation nanophotonic devices due to the high optical confinement, low optical losses, and long lifetime. It is crucial to modulate the PhPs in already discovered materials in order to utilize PhPs efficiently and increase the device operability. In this work, oriented particle trace structures in α‐MoO3 are generated where the dielectric functions are broken by proton irradiation. Those particle trace structures act as in‐plane boundaries, launching and reflecting PhPs. In‐plane needle‐like PhPs in the intermediate state are obtained and finally the switching‐off of PhPs via increasing the irradiation fluences is achieved. Furthermore, the switching‐off PhPs are partly restored to original state by annealing. The method provides an opportunity to manipulate light at the nanoscale and construct in‐plane PhPs reflectors with the potential to be used for polaritonic devices and circuits. [ABSTRACT FROM AUTHOR]

Anisotropic hyperbolic phonon‐polaritons (HPhPs) in a van der Waals material, orthorhombic‐phase molybdenum trioxide (α‐MoO3), provide strategies in multiple dimensions to manipulate photons at the nanoscale. However, the nano‐imaging studies of the in‐plane HPhPs along orthogonal crystal orientations are still rare. In this work, the launching and propagating properties of HPhPs are studied in α‐MoO3 upon a holey silicon nitride microcavity through a photon‐induced force microscope (PiFM) over a broad tunable mid‐infrared region of 780–1010 cm−1. Near‐field patterns stemming from the orthogonal polariton momenta are observed in this spectral band. A simple model based on the geometrical optics of elliptic resonance cones is used to explain the near‐field phonon‐polariton features. These near‐field optical properties indicate abundantly possible operations and applications for nanophotonics. [ABSTRACT FROM AUTHOR]

Siliceous diatom frustules present a huge variety of shapes and nanometric pore patterns. A better understanding of the light modulation by these frustules is required to determine whether or not they might have photobiological roles besides their possible utilization as building blocks in photonic applications. In this study, we propose a novel approach for analyzing the near-field light modulation by small pennate diatom frustules, utilizing the frustule of Gomphonema parvulum as a model. Numerical analysis was carried out for the wave propagation across selected 2D cross-sections in a statistically representative 3D model for the valve based on the finite element frequency domain method. The influences of light wavelength (vacuum wavelengths from 300 to 800 nm) and refractive index changes, as well as structural parameters, on the light modulation were investigated and compared to theoretical predictions when possible. The results showed complex interference patterns resulting from the overlay of different optical phenomena, which can be explained by the presence of a few integrated optical components in the valve. Moreover, studies on the complete frustule in an aqueous medium allow the discussion of its possible photobiological relevance. Furthermore, our results may enable the simple screening of unstudied pennate frustules for photonic applications. [ABSTRACT FROM AUTHOR]

Second harmonic generation (SHG) is a nonlinear optical response arising exclusively from broken inversion symmetry in the electric‐dipole limit. Recently, SHG has attracted widespread interest as a versatile and noninvasive tool for characterization of crystal symmetry and emerging ferroic or topological orders in quantum materials. However, conventional far‐field optics is unable to probe local symmetry at the deep subwavelength scale. Here, near‐field SHG imaging of 2D semiconductors and heterostructures with the spatial resolution down to 20 nm is demonstrated using a scattering‐type nano‐optical apparatus. It is shown that near‐field SHG efficiency is greatly enhanced by excitons in atomically thin transition metal dichalcogenides. Furthermore, by correlating nonlinear and linear scattering‐type nano‐imaging, nanoscale variations of interlayer stacking order in bilayer WSe2 are resolved, and the stacking‐tuned excitonic light–matter interactions are revealed. This work demonstrates nonlinear optical interrogation of crystal symmetry and structure–property relationships at the nanometer length scales relevant to emerging properties in quantum materials. [ABSTRACT FROM AUTHOR]

We study how nanophotonic structures can be used for determining the position of a nearby nanoscale object with subwavelength accuracy. Through perturbing the near-field environment of a metasurface transducer consisting of nano-apertures in a metallic film, the location of the nanoscale object is transduced into the transducer’s far-field optical response. By monitoring the scattering pattern of the nanophotonic near-field transducer and comparing it to measured reference data, we demonstrate the two-dimensional localization of the object accurate to 24 nm across an area of 2 × 2 μm. We find that adding complexity to the nanophotonic transducer allows localization over a larger area while maintaining resolution, as it enables encoding more information on the position of the object in the transducer’s far-field response.

Optical metamaterials offer precise control over the properties and interactions of light at the nanoscale, attracting interest in many new fields of research including chemical and molecular sensing, magnetic antennas, and photovoltaic elements. By utilizing the phenomenon of extraordinary optical transmission (EOT) plasmonic devices enable the detection of minute changes in the local, near‐surface, dielectric properties of materials, opening up a wide range of different applications. Characterization of the optoelectronic properties of ultra‐thin films is of paramount importance for a wide range of electronic applications including integrated circuit production. However, it is often extremely difficult to achieve using conventional imaging techniques. Here, it is demonstrated that plasmonic color filters can be used for the direct optical imaging and characterization of ion implantation in thin films. A model system consisting of variable doses of gallium ions implanted within titanium oxide thin films is used. It is observed that the ion implantation dose leads to a variation in the measured plasmon resonance spectra, which can be further enhanced through the use of bimodal nanopixel arrays. Using Monte Carlo simulations and the Maxwell‐Garnett relation, the observed plasmon resonance spectra in terms of the gallium ion implantation dose is quantitatively interpreted. [ABSTRACT FROM AUTHOR]

We propose a nanospaser made of an achiral plasmonic–metal nanodisk and a two-dimensional chiral gain medium – a monolayer nanoflake of a transition-metal dichalcogenide (TMDC). When one valley of the TMDC is selectively pumped (e.g. by a circular-polarized radiation), the spaser (surface plasmon amplification by stimulated emission of radiation) generates a mode carrying a topological chiral charge that matches that of the gain valley. There is another, chirally mismatched, time-reversed mode with exactly the same frequency but the opposite topological charge; it is actively suppressed by the gain saturation and never generates, leading to a strong topological protection for the generating matched mode. This topological spaser is promising for use in nano-optics and nanospectroscopy in the near field especially in applications to biomolecules that are typically chiral. Another potential application is a chiral nanolabel for biomedical applications emitting in the far field an intense circularly polarized coherent radiation.

The electromagnetic properties of ordered hole nanostructures in very thin metal films are characterized using CdSe/CdS nanocrystals (NCs) as nanoprobes. The characterization of the local density of optical states (LDOS) on the nanostructure is possible by the measurement of their photoluminescence decay rate. Statistical measurements are performed in the far field to show the average increase of optical modes. A determinist approach using an active single NC nanoprobe in the near field gives access to a more precise characterization of the LDOS. The optical properties of the structure come from the coupling between localized surface plasmons created by the holes and surface plasmon polaritons. A strong concentration of optical modes is observed around the holes thanks to the active near-field nanoprobe. With different NC orientations, the strong influence of the component perpendicular to the surface in the very near field of the LDOS is observed. Finite differential time domain simulations of the different components of the electric field in the very near field of the structure confirm that the localization of the electric field around the holes is only due to the normal component as observed with the nanoprobe.

Siliceous diatom frustules present a huge variety of shapes and nanometric pore patterns. A better understanding of the light modulation by these frustules is required to determine whether or not they might have photobiological roles besides their possible utilization as building blocks in photonic applications. In this study, we propose a novel approach for analyzing the near-field light modulation by small pennate diatom frustules, utilizing the frustule of Gomphonema parvulum as a model. Numerical analysis was carried out for the wave propagation across selected 2D cross-sections in a statistically representative 3D model for the valve based on the finite element frequency domain method. The influences of light wavelength (vacuum wavelengths from 300 to 800 nm) and refractive index changes, as well as structural parameters, on the light modulation were investigated and compared to theoretical predictions when possible. The results showed complex interference patterns resulting from the overlay of different optical phenomena, which can be explained by the presence of a few integrated optical components in the valve. Moreover, studies on the complete frustule in an aqueous medium allow the discussion of its possible photobiological relevance. Furthermore, our results may enable the simple screening of unstudied pennate frustules for photonic applications.

Abstract Background In recent years, our group has developed electro-optical remote sensing methods for the monitoring and classification of aerofauna. These methods include active lidar methods and passive, so-called dark-field methods that measure scattered sunlight. In comparison with satellite- and airborne remote sensing, our methods offer a spatiotemporal resolution several orders of magnitude higher, and unlike radar, they can be employed close to ground. Whereas passive methods are desirable due to lower power consumption and ease of use, they have until now lacked ranging capabilities. Results In this work, we demonstrate how passive ranging of sparse insects transiting the probe volume can be achieved with quadrant sensors. Insects are simulated in a raytracing model of the probe volume, and a ranging equation is devised based on the simulations. The ranging equation is implemented and validated with field data, and system parameters that vary with range are investigated. A model for estimating insect flight headings with modulation spectroscopy is implemented and tested with inconclusive results. Insect fluxes are retrieved through time-lag correlation of quadrant detector segments, showing that insects flew more with than against the wind during the study period. Conclusions The presented method demonstrates how ranging can be achieved with quadrant sensors, and how it can be implemented with or without active illumination. A number of insect flight parameters can be extracted from the data produced by the sensor and correlated with complementary information about weather and topography. The approach has the potential to become a widespread and simple tool for monitoring abundances and fluxes of pests and disease vectors in the atmosphere.

Two-dimensional (2D) semiconductors, such as transition metal dichalcogenides, have emerged as important candidate materials for next-generation chip-scale optoelectronic devices with the development of large-scale production techniques, such as chemical vapor deposition (CVD). However, 2D materials need to be transferred to other target substrates after growth, during which various micro- and nanoscale defects, such as nanobubbles, are inevitably generated. These nanodefects not only influence the uniformity of 2D semiconductors but also may significantly alter the local optoelectronic properties of the composed devices. Hence, super-resolution discrimination and characterization of nanodefects are highly demanded. Here, we report a near-field nanophotoluminescence (nano-PL) microscope that can quickly screen nanobubbles and investigate their impact on local excitonic properties of 2D semiconductors by directly visualize the PL emission distribution with a very high spatial resolution of ∼10 nm, far below the optical diffraction limit, and a high speed of 10 ms/point under ambient conditions. By using nano-PL microscopy to map the exciton and trion emission intensity distributions in transferred CVD-grown monolayer tungsten disulfide (1L-WS 2 ) flakes, it is found that the PL intensity decreases by 13.4% as the height of the nanobubble increases by every nanometer, which is mainly caused by the suppression of trion emission due to the strong doping effect from the substrate. In addition to the nanobubbles, other types of nanodefects, such as cracks, stacks, and grain boundaries, can also be characterized. The nano-PL method is proven to be a powerful tool for the nondestructive quality inspection of nanodefects as well as the super-resolution exploration of local optoelectronic properties of 2D materials.

Abstract A review of recent progress in optical recording of surface relief structures in the films of two classes of photoresponsive non-crystalline materials (azobenzene-containing polymers and amorphous chalcogenides) is presented. Various aspects related to light-driven macroscopic effects for these materials where stimulated surface patterning through selective mass transport process due to the interaction of matter with polarized light are discussed. Self-assembling processes initiated by polarized light illumination resulting in the formation of multiscale periodic reliefs on the photosensitive material surface are analyzed. Extensive experimental data describing different aspects of photomanipulated surface relief patterning using vectorial optical fields and structured light beams are summarized. Anisotropic nanoscale motion in amorphous azopolymer and chalcogenide films induced by a tightly focused polarized laser beam is considered. Similarities and differences in the manifestation of competition and cooperation between polarization-driven and intensity-driven mechanisms responsible for material displacement in chalcogenide glasses and amorphous azopolymers are analyzed. Possibilities for optimization and speeding up the process of holographic recording of periodic relief gratings in amorphous azopolymer and chalcogenide films at various configurations for combination of optical beams to produce 2D and 3D relief architecture on the film surface are discussed. Highlights • Optical patterning in azopolymers and amorphous chalcogenides is reviewed. • Self-assembling due to polarized light illumination results in periodic reliefs. • Polarization- and intensity-driven mechanisms are responsible for mass transport [ABSTRACT FROM AUTHOR]

Plasmonic optical tweezers can overcome the diffraction limits of conventional optical tweezers and enable the trapping of nanoscale objects. Extension of the trapping and manipulation of nanoscale objects with nanometer position precision opens up unprecedented opportunities for applications in the fields of biology, chemistry and statistical and atomic physics. Potential applications include direct molecular manipulation, lab-on-a-chip applications for viruses and vesicles and the study of nanoscale transport. This paper reviews the recent research progress and development bottlenecks and provides an overview of possible future directions in this field.

The terahertz (THz) frequency range is key to studying collective excitations in many crystals and organic molecules. However, due to the large wavelength of THz radiation, the local probing of these excitations in smaller crystalline structures or few-molecule arrangements requires sophisticated methods to confine THz light down to the nanometer length scale, as well as to manipulate such a confined radiation. For this purpose, in recent years, taking advantage of hyperbolic phonon polaritons (HPhPs) in highly anisotropic van der Waals (vdW) materials has emerged as a promising approach, offering a multitude of manipulation options, such as control over the wavefront shape and propagation direction. Here, we demonstrate the THz application of twist-angle-induced HPhP manipulation, designing the propagation of confined THz radiation between 8.39 and 8.98 THz in the vdW material α-molybdenum trioxide (α-MoO 3 ), hence extending twistoptics to this intriguing frequency range. Our images, recorded by near-field optical microscopy, show the frequency- and twist-angle-dependent changes between hyperbolic and elliptic polariton propagation, revealing a polaritonic transition at THz frequencies. As a result, we are able to allocate canalization (highly collimated propagation) of confined THz radiation by carefully adjusting these two parameters, i.e. frequency and twist angle. Specifically, we report polariton canalization in α-MoO 3 at 8.67 THz for a twist angle of 50°. Our results demonstrate the precise control and manipulation of confined collective excitations at THz frequencies, particularly offering possibilities for nanophotonic applications.

Abstract: The ability to manipulate small objects with focused laser beams has opened a venue for investigating dynamical phenomena relevant to both fundamental and applied sciences. However, manipulating nano‐sized objects requires subwavelength field localization, provided by auxiliary nano‐ and microstructures. Particularly, dielectric microparticles can be used to confine light to an intense beam with a subwavelength waist, called a photonic nanojet (PNJ), which can provide sufficient field gradients for trapping nano‐objects. Herein, the scheme for wavelength‐tunable and nanoscale‐precise optical trapping is elaborated, and the possibility of lateral nanoparticle movement using the PNJ's side lobes is shown for the first time. In addition, the possibility of subwavelength positioning using polarization switching is shown. The estimated stability with respect to Brownian motion is higher compared to conventional optical trapping schemes. [ABSTRACT FROM AUTHOR]

This paper is concerned with the inverse problem of reconstructing small and local perturbations of a planar surface using the field interaction between a known plasmonic particle and the planar surface. The aim is to perform a super-resolved reconstruction of these perturbations from shifts in the plasmonic frequencies of the particle-surface system. In order to analyse the interaction between the plasmonic particle and the planar surface, a well-chosen conformal mapping, which transforms the particlesurface system into a coated structure, is used. Then the even Fourier coefficients of the transformed domain are related to the shifts in the plasmonic resonances of the particle-surface system. A direct reconstruction of the perturbations of the planar surface is proposed. Its viability and limitations are documented by numerical examples. [ABSTRACT FROM AUTHOR]

Abstract: Photonic jets are normally generated in transmission mode and are represented as a spatially localized high‐intensity region on the shadow side of a particle‐lens, with a background to medium refractive index contrast of 1.3–1.7 while illuminated by a plane wave. Here, a photonic jet is discovered in the opposing plane wave propagation direction and lies in the area in the upper boundary of a near‐unity refractive index sphere on a high refractive index dielectric substrate. The redistribution of the power flow is inhibited during the reflected wave passing the near‐unity refractive index sphere. This has led to a unique effect on the focus position and shape of the produced photonic jet in reflection mode which can be maximally maintained near the sphere regardless of the modulation of the refractive index for the dielectric substrate material. [ABSTRACT FROM AUTHOR]

Abstract: A particle can function as a refractive lens to focus a plane wave, generating a narrow, high intensive, weak‐diverging beam within a sub‐wavelength volume, known as the ‘photonic nanojet’. It is known that apodization method, in the form of an amplitude pupil‐mask centrally situated on a particle‐lens, can further reduce the waist of a photonic nanojet, however, it usually lowers the intensity at the focus due to blocking the incident light. In this paper, the anomalously intensity‐enhanced apodization effect was discovered for the first time via numerical simulation of focusing of the axially illuminated circular‐column particle‐lenses, and a greater than 100% peak intensity increase was realised for the produced photonic nanojets. [ABSTRACT FROM AUTHOR]

Typical measurements of light in the near-field utilize a photodetector such as a photomultiplier tube or a photodiode, which is placed remotely from the region under test. This kind of detection has many draw-backs including the necessity to detect light in the far-field, the influence of background propagating radiation, the relatively narrowband operation of photodetectors which complicates the operation over a wide wavelength range, and the difficulty in detecting radiation in the far-IR and THz. Here we review an alternative near-field light measurement technique based on the detection of optically induced forces acting on the scanning probe. This type of detection overcomes some of the above limitations, permitting true broad-band detection of light directly in the near-field with a single detector. The physical origins and the main characteristics of optical force detection are reviewed. In addition, intrinsic effects of the inherent optical forces for certain operation modalities of scanning probe microscopy are discussed. Finally, we review practical applications of optical force detection of interest for the broader field of the scanning probe microscopy.

An overview of near-field optics is presented with a focus on the fundamental advances that have been made in the field since its inception 30 years ago. A focus is placed on the advancements that have been achieved in instrumentation. These advances have led to a greater generality of use with ultra-low mechanical and optical noise and the ultimate in force sensitivity with near-field optical probes. An emphasis is placed on the importance of fully integrating near-field optics with other imaging and spectroscopic modalities including Raman spectroscopy and electron/ion beam imaging. Important directions in probe design, force feedback methods and scanner flexibility are described. These developing avenues provide considerable optimism for an ever increasing incorporation of near-field optics to help resolve critical problems in fundamental and applied science.

Two-dimensional (2D) materials provide a platform for strong light-matter interactions, creating wide-ranging design opportunities via new-material discoveries and new methods for geometrical structuring. We derive general upper bounds to the strength of such light-matter interactions, given only the optical conductivity of the material, including spatial nonlocality, and otherwise independent of shape and configuration. Our material figure-of-merit shows that highly doped graphene is an optimal material at infrared frequencies, whereas single-atomic-layer silver is optimal in the visible. For quantities ranging from absorption and scattering to near-field spontaneous-emission enhancements and radiative heat transfer, we consider canonical geometrical structures and show that in certain cases the bounds can be approached, while in others there may be significant opportunity for design improvement. The bounds can encourage systematic improvements in the design of ultrathin broadband absorbers, 2D antennas, and near-field energy harvesters. [ABSTRACT FROM AUTHOR]

An electromagnetic theory of thermal radiation is outlined, based on the fluctuation electrodynamics of Rytov and co-workers. We discuss the basic concepts and the status of different approximations. The physical content is illustrated with a few examples on near-field heat transfer. [ABSTRACT FROM AUTHOR]

Collimated Gaussian beams are efficiently localized at the apex of a metal-coated axicon prism by surface plasmon excitations. We observed the light scattered at the apex and the light reflected by the prism. Intense scattered light was observed with the radial polarization incidence. Further, each incidence of the radial, azimuthal, and linear polarizations provided field distributions of bright and dark intensities in the reflected images according to the surface plasmon excitation. We have demonstrated that surface plasmon waves are excited at the sides of the prism in the Kretschmann configuration and that they converge to its apex.

We have developed a novel nanoscale temperature-measurement method using fluorescence in the near-field called Fluorescence Near-field Optics Thermal Nanoscopy (Fluor-NOTN). Fluor-NOTN enables the temperature distributions of nanoscale materials to be measured in vivo/in situ. The proposed method measures temperature by detecting the temperature dependent fluorescence lifetimes of Cd/Se Quantum Dots (QDs). For a high-sensitivity temperature measurement, the auto-fluorescence generated from a fiber probe should be reduced. In order to decrease the noise, we have fabricated a novel near-field optical-fiber probe by fusion-splicing a photonic crystal fiber (PCF) and a conventional single-mode fiber (SMF). The validity of the novel fiber probe was assessed experimentally by evaluating the auto-fluorescence spectra of the PCF. Due to the decrease of auto-fluorescence, a six- to ten-fold increase of S/N in the near-field fluorescence lifetime detection was achieved with the newly fabricated fusion-spliced near-field optical fiber probe. Additionally, the near-field fluorescence lifetime of the quantum dots was successfully measured by the fabricated fusion-spliced near-field optical fiber probe at room temperature, and was estimated to be 10.0 ns.