Characterisation of the influence of multi-quantum barrier reflectors within GaInP/AlGaInP quantum well lasers using near-field imaging techniques

Using a near-field scanning optical microscope, near-field photocurrent and topographic imaging has measured the effect on intrinsic electric fields and photocurrent propagation resulting from inserting multi-quantum barrier (MQB) super-lattices into quantum well lasers. Measurements on devices at two different excitation wavelengths have highlighted the sensitivity of the near-field optical technique. Strong correlations were seen in the photocurrent response of the multi-quantum barrier regions when compared with simulations made on the electric field generated within the structure. As a result, photocurrent attenuation was attributed to carrier confinement in these barrier regions when compared to a control sample. The measurements illustrate the effectiveness of the MQB, in addition to the sensitivity and power of the near-field photocurrent technique.     

Near-field scanning optical microscopy studies of thin film surfaces and interfaces

In this article, the results of the modeling of topography related artifacts appearing in near-field scanning optical microscopy measurements are presented. The results obtained for near-field scanning optical microscope operation in reflection mode with off-axis far field detector position are compared with experimental results. It is shown that the chosen numerical method - Finite Difference in Time Domain method (FDTD) - can be used for efficient modeling of main topography related artifact. It is also seen that the far field detector position can have large influence on the resulting reflection mode optical images.     

Optical near-field microscopy of light focusing through a photonic crystal flat lens

We report here the direct observation by using a scanning near-field microscopy technique of the light focusing through a photonic crystal flat lens designed and fabricated to operate at optical frequencies. The lens is fabricated using a III-V semiconductor slab, and we directly visualize the propagation of the electromagnetic waves by using a scanning near-field optical microscope. We directly evidence spatially, as well as spectrally, the focusing operating regime of the lens. At last, in light of the experimental scanning near-field optical microscope pictures, we discuss the lens ability to focus light at a subwavelength scale.     

Laser nanotraps and nanotweezers for cold atoms: 3D gradient dipole force trap in the vicinity of scanning near-field optical microscope tip

Using a two-dipole model of an optical near-field of scanning near-field optical microscope tip, i.e., taking into account contributions of magnetic and electric dipoles, we propose and analyze a new type of 3D optical nanotrap found for certain relations between electric and magnetic dipoles. Electric field attains a minimum value in vacuum in the vicinity of the tip and hence such a trap is quite suitable for manipulations with cold atoms.     

Near-field optical microscopy using an integrating sphere

A scanning near-field optical microscope using an integrating sphere is demonstrated. The images from a usual near-field optical microscope often include contrasts caused by the sample structure because the reflection and transmission angles of signal waves depend on the size and shape of the sample. The observation angle dependency of signals can be avoided by using an integrating sphere. Background signals resulting from using the sphere can be reduced by using lock-in detection synchronously with modulation of tip–sample distance. The whole detection system is possibly useful for observing the distribution of the refractive index and/or the absorption coefficient. Received: 27 October 2000 / Final version: 29 August 2001 / Published online: 7 November 2001     

新型扫描近场微波显微术

简要回顾了近场显微术,特别是扫描近场微波显微术的发展历史;简要介绍了一种新型扫描近场微波显微镜的结构、工作原理以及相应的微波近场显微波近场显微理论;介绍了它在超导材料、铁电材料、高密度存储技术研究中的应用。     

Near-field optical microscope with a multiheight scanning imaging mode

A near-field scanning optical microscope has been developed to yield optical images with various gap distances between the probe and the sample surface. The microscope uses an apertureless metallic probe, the position of which is controlled by regulation of the tunneling-electron current from the probe to the sample and by computer-generated bias voltage. Experimental results of near-field optical imaging with the developed microscope at different gap distances are shown. Thirteen images at gap distances of 0 to 500nm demonstrate that the near-field image depends strongly on the gap distance. The imaging characteristics of a near-field imaging system are shown with the spatial-frequency spectra of images. Future investigation of the developed microscope is also discussed.     

基于迈克耳孙干涉仪的近场光学实验

介绍了一种以迈克耳孙干涉仪作为操作平台的近场光学实验系统.该系统可以测量棱镜内表面全内反射产生的隐失场,观察两维光栅样品的近场光学结构,还可以用于光子扫描隧穿显微镜(PSTM)的原理性实验,有助于学生深入了解隐失场的结构和近场光学显微镜的基本工作原理.该装置具有结构简单可靠,操作简便等特点,十分适用于物理实验教学.     

Laser-tweezer-controlled solid immersion microscopy in microfluidic systems

We describe the creation and implementation of a near-field scanning solid immersion microscope that is specifically tailored for use in microfluidic systems. The microscope comprises a newly fabricated Weierstrass solid immersion lens (SIL), which is detached from its substrate and is free floating in the fluid, and a laser optical tweezer, which serves both as a trapping beam for alignment and positioning of the SIL and as a near-field scanning beam that images the sample through the SIL. A discussion of the SIL's fabrication method is presented along with experimental results that demonstrate the effectiveness of our microscope design.     

Hard disk magnetic domain nano-spatial resolution imaging by using a near-field scanning microwave microscope with an AFM probe tip

A near-field scanning microwave microscope (NSMM) incorporating an atomic force microscope (AFM) probe tip was used for the direct imaging of magnetic domains of a hard disk under an external magnetic field. We directly imaged the magnetic domain changes by measuring the change of reflection coefficient S₁₁ of the NSMM at an operating frequency near 4.4 GHz. Comparison was made to the magnetic force microscope (MFM) image. Using the AFM probe tip coupled to the tuning fork distance control system enabled nano-spatial resolution. The NSMM incorporating an AFM tip offers a reliable means for quantitative measurement of magnetic domains with nano-scale resolution and high sensitivity.     

Near-Field Fluorescence and Topography Characterization of a Single Nanometre Fluorophore by Apertureless Tip-Enhanced Scanning Near-Field Microscopy

Tip-enhanced near-field fluorescence and topography characterization of a single nanometre fluorophore is conducted by using an apertureless scanning near-field microscopy system. A fluorophore with size 80hm is mapped with a spatial resolution of 10hm. The corresponding near-field fluorescence data shows significant signal enhancement due to the apertureless tip-enhanced effect. With the nanometre spatial resolution capability and nanometre local tip-enhanced effect, the apertureless tip-enhanced scanning near-field microscopy may be further used to characterize a single molecule by realizing the local near-field spectrum assignment corresponding to topography at nanometre scale.     

Theoretical near-field optical properties of branched plasmonic nanoparticle networks

Extended branched networks of single-nanoparticle chains have recently been self-assembled from colloidal suspensions. In particular, gold nanoparticle linear chains and complex chain networks have revealed unique signatures of plasmon modes in their extinction spectra. In this Letter, we investigate theoretically their near-field optical properties and show that a real space mapping of these modes can be achieved with a photon scanning tunneling microscope setup. A distinct subwavelength patterning of the optical near-field gives rise to well-resolved photon scanning tunneling microscope images that can be used to identify the network segments able to efficiently carry optical energy.     

The role of propagating and evanescent waves in scanning near-field optical microscopy

Theoretical study on the image formation in scanning near-field optical microscopy is carried out in the framework of the direct moment method. Information brought, respectively, by the propagating and evanescent components in the optical near field that is collected by a scanning fiber tip with a sub-wavelength aperture is numerically and systematically analyzed in the light of the resolution achieved by the microscope. The analyses reveal that resolutions beyond the diffraction limit can be achieved even in the absence of the evanescent waves. That is, it is incorrect or at least incomplete to believe that a microscope that collects only the propagating waves is limited by the diffraction. Our studies show that a scanning near-field optical microscope can achieve resolutions beyond the diffraction limit by collecting only the propagating waves.     

Imaging the local density of states of optical corrals

This paper reports the experimental observation, at optical frequencies, of the electromagnetic local density of states established by nanostructures corresponding to the recently introduced concept of optical corral [G. Colas des Francs et al., Phys. Rev. Lett. 86, 4950 (2001)]. The images obtained by a scanning near-field optical microscope under specific operational conditions are found in agreement with the theoretical maps of the optical local density of states. A clear functionality of detection by the scanning near-field optical microscope is thereby identified since the theoretical maps are computed without including any specific tip model.     

Characterization of strong electromagnetic field confinement on gold nanostructures by apertureless scanning near-field optical microscopy

We report on the detection of the optical near field of a 1D gold particle array by using an apertureless scanning near-field optical microscope. The strong near-field confinement measured above the grating proves unambiguously the near-field origin of the detected optical signal. Comparing the experiment with theory leads us to assign the optical near field to the first diffracted order of the grating, which is evanescent.     

SNOM Observations of Surface Plasmon Polaritons on Metal Heterostructures

We observe surface plasmon polariton （SPP） refraction on a metal heterostructured sample with a scattered-type scanning near-field optical microscope （SNOM）. The sample consists of AI and Au in-plane whose boundary is smooth enough with proper etching time. SPPs excited on the AI film travel to the boundary and a portion of SPPs propagates into the Au film. In addition, interference fringes appear in the SNOM image bent at the boundary. The result is analysed with effective index method and the refracted angle is explained by Shell＇s law.     

Review of near-field optical microscopy

This review has introduced a new near-field optical microscope (NOM)—atomic force microscope combined with photon scanning tunneling microscope (AF / PSTM). During scanning, AF/PSTM could get two optical images of refractive index image and transmissivity image, and two AFM images of topography image and phase image. A reflected near-field optical microscope (AF/RSNOM) has also been developed on AF/PSTM platform. The NOM has been reviewed in this paper and the comparison between AF/PSTM & RSNOM and the commercial A-SNOM & RNOM has also been discussed. The functions of AF/PSTM & RSNOM are much better than A-SNOM & RNOM.     

Development of Scanning Near-Field Optical Microscope Working under Cryogenic Temperature and Strong Magnetic Field

We report on the development of a cantilever-based scanning near-field optical microscope (SNOM) working in an extreme environment, at cryogenic temperature around 10 K and under strong magnetic field up to 7 T. We designed a new optical system based on an infinite conjugate microscope, which extracts the near-field signal from a small aperture through a narrow chamber into free space as collimated light. Using this system, we successfully measured near-field and topographical images of a metal-hole sample simultaneously. Combining the local optical accessing technique with the external control of the electronic state, this SNOM system will be a powerful tool to study optical properties of semiconductor nanostructures.     

Surface plasmon mediated near-field imaging and optical addressing in nanoscience

We present an overview of recent progress in "plasmonics". We focus our study on the observation and excitation of surface plasmon polaritons (SPPs) with optical near-field microscopy. We discuss in particular recent applications of photon scanning tunnelling microscope (PSTM) for imaging of SPP propagating in metal and dielectric wave guides. We show how near-field scanning optical microscopy (NSOM) can be used to optically and actively address remote nano objects such as quantum dots. Additionally we compare results obtained with near-field microcopy to those obtained with other optical far-field methods of analysis such as leakage radiation microscopy (LRM).