A magneto-optic Kerr effect scanning near-field optical microscope is used to image a stripe domain wall in a Co/Pt multilayer sample. The microscope is an improved version of a type previously reported, which uses light scattering from surface plasmons in 20 - 40 nm Ag particles as a near-field probe. Data is presented for both the probe intensity and polarization contrast as a function of probe/sample spacing. Oscillatory behavior in both sets of data is reasonably explained with a simplified model of optical interference.

A theory is developed for the magneto-optic Kerr effect (MOKE) excited via an optical near field. The model under consideration includes a semi-infinite ferromagnet and a small non- magnetic metal particle which is located nearby and possesses a long-living surface plasmon. A multiple-scattering formulation of the problem is given. Considering the Rayleigh scattering of light and the magneto-optical light polarization conversion as elementary events, all the essential optical processes are classified, and those which contribute to the near-field MOKE are treated separately. An effective particle polarizability, responsible for a near-field excitation, is treated self-consistently to all orders in light-matter scattered light field is discussed with special emphasis on the change of optical polarization due to MOKE.

An expression of evanescent field of the scanning near-field optical microscope (SNOM) and a few effects on the resolving power are given. The concept about degrees of freedom of light information transmitted and resolution of SNOM are reviewed.

The foundation for the invention of the photon scanning tunneling microscope (PSTM) are the near field scanning optical microscope, the optical fiber technique, the total internal reflection, high sensitive opto-electronic detecting technique and computer technique etc. Recent research results show the subwavelength resolution of 1 - 3 nm is obtained. How to explain the PSTM has got such high subwavelength resolution? What value is the PSTM's limiting of subwavelength resolution? For resolving these problems this paper presented a photon theory hypothesis about PSTM that is based on the following two basic laws: (1) Photon is not only a carrier bringing energy and optical information, but also is a particle occupied fixed space size. (2) When a photon happened reflection, refraction, scattering, etc., only changed its energy and optical information carried, its particle size doesn't change. g (DOT) p_photon equals constant. Using these two basic laws to PSTM, the `evanescent field' is practically a weak photon distribution field and the detecting fiber tip diameter is practically a `gate' which size controlled the photon numbers into fiber tip. Passing through some calculation and inference, the following three conclusions can be given: (1) Under the PSTM's detection system sensitivity is high enough, the diameter D of detecting fiber tip and the near field detecting distance Z are the two most important factors to decide the subwavelength resolution of PSTM. (2) The limiting of PSTM's resolution will be given upon the conditions of D equals p_photon and Z equals p_photon, where p_photon is one photon size. (2) The final resolution limit R of PSTM will be lim R equals p_photon, D yields p_photon, Z yields p_photon.

Near-field Scanning Optical Microscopy (NSOM) is a true optical microscopic technique allowing fluorescence, absorption, reflection and polarization contrast with the additional advantage of nanometer lateral resolution, unlimited by diffraction and operation at ambient conditions. NSOM based on metal coated adiabatically tapered fibers, combined with shear force feedback and operated in illumination mode, has proven to be the most powerful NSOM arrangement, because of its true localization of the optical interaction, its various optical contrast possibilities and its sensitivity down to the single molecular level. In this paper applications of `aperture' NSOM to Fluorescence In Situ Hybridization of human metaphase chromosomes are presented, where the localized fluorescence allows to identify specific DNA sequences. All images are accompanied by the simultaneously acquired force image, enabling direct comparison of the optical contrast with the sample topography on nanometer scale, far beyond the diffraction limit. Thus the unique combination of high resolution, specific optical contrast and ambient operation offers many new direction possibilities in biological studies.

Although the advance of near field optics gives us the ability to achieve sub-wavelength resolution in microscopy, so far its application to chemistry and biology has been mostly limited to fluorescence and transmission imaging. In this study we propose a new method, namely using the nonlinear near field optics properties to study the material interactions directly, by wave-mixing the near field and the external pumping field. Using this method, one can study the rich non-linear spectroscopic properties of many systems with the added bonus of near field resolution.

Some problems in a near-field scanning optical microscope (NSOM) system for observing biological living specimens is discussed. The NSOM system works based on the principle of nano-optics and near-field optics. Propagating characteristics of evanescent wave field, the effects of absorption, polarization changes, fluorescence, optical density, refractive index, luminescence and incident angle are analyzed. Methods eliminating pseudo-image in specimens are proposed. NSOM will be employed to conduct investigation of single molecule of living biological specimen and make precision metrology researches in nanometer scale.

Light emitted from the aperture of a near-field optical probe in the close vicinity of a dielectric object propagates in classically `forbidden' as well as `allowed' directions; the two zones are separated by the critical angle for total internal reflection. The new `tunnel' near-field optical microscopy (TNOM) technique makes use of forbidden and allowed radiation, in contrast to standard scanning near-field optical microscopy (SNOM or NSOM), which records only the allowed light. Scan images obtained with allowed and forbidden light are complementary to some extent; the latter, however, provide high contrast and resolution even in situations in which standard SNOM/NSOM shows little or no contrast. The influence of topography on image formation is analyzed and discussed.

In a recent paper we have developed a new technique allowing to control the distance separation between a tapered metal coated optical fiber tip and the surface of a sample. This technique is based on a piezo-electric tuning fork as a shear force sensor and is found to be suitable for the operation of near-field scanning optical microscope. We present in this article a review of the recent results concerning this new technique. In particular, we present hydrodynamic measurements performed in order to evaluate the shear (or viscous drag) forces picked up by the piezo-electric tuning fork sensor.

This paper describes the design and applications to optical processing and recording of a Scanning Near-field Optic/Atomic-force Microscope (SNOAM). A sharpened and bent optical fiber was used as a near-field optical probe as well as an atomic force microscope probe in a vertical vibrating mode. SNOAM provides simultaneous topographical and optical images with high resolution beyond the diffraction limit. As an example of an application to optical processing, near-field exposures have been demonstrated by a SNOAM. We produced pit and line patterns exposed and developed in commercial photoresist film. In the processing mode, the pit and line patterns down to a width of 100 nm have been fabricated on a Si wafer through the Integrated Circuits process.

We describe a new system for controlling the tip-to-sample separation in a Near Field Scanning Optical Microscope. A tapered Al coated fiber was glued to a high-Q Si paddle mechanical oscillator. The paddle is capacitively driven at one of its resonances, and the amplitude of the movement is detected through another electrode. As the tip approaches the surface, the viscous drag acting on its increases, causing the amplitude of oscillation of the paddle-tip system to reduce. A signal proportional to the amplitude of oscillation is used as feedback to control the tip-to-sample distance. This is accomplished in the 0 - 200 nm range, with a stability better than 1 nm. We present a complete characterization of the system. In order to determine the capabilities of our setup we provide shear force images of different samples as well as simultaneous topographic and near field images of GaAs/AlGaAs 1.55 micrometers waveguides.

In measurements of sample temporal response with a near-field scanning optical microscope, or NSOM, one must account for the temporal response of the probe. The coupling of thermal and temporal effects in an NSOM fitted with a coated tapered fiber probe is considered. Study of the perturbation of cw infrared light by a pulse of visible light simultaneously sent through an illumination mode NSOM allows one to separate the relatively slow thermal response of the probe from the appreciably faster response of a silicon sample imaged with the probe. Temporal and thermal contrast in NSOM imaging are discussed in terms of the results.

A Fluorescence Scanning Near-Field Optical Microscope operated in reflection is presented. A pulled optical fiber is used both as an emitter for the exciting light and a collector for the generated fluorescence. The advantage of this set-up is the use of the fiber tip as an emitter and a collector. The sample is locally illuminated and no extra optical elements are needed for the detection. We will describe the shear force set-up which is used to control the tip to surface distance. Direct correlation between force map and optical signal is thus possible. Fluorescence images have been obtained on Langmuir-Blodgett films where we estimate the resolution at 200 nm. Moreover the anisotropic property of the monolayer allows polarization contrast measurements. Thus, we show true optical contrast due to fluorescence and polarization is applicable to this configuration. Artifacts in LB films shear force image are discussed. Shear force approach curves obtained on glass and polymer domains are presented to explain the chemical origin of the phenomenon.

Uncertainty in tip morphology of aluminum coated, fiber-optic near-field probes, and the large difference between the physical probe diameter and (smaller) optical diameter, lead to serious imaging artifacts in transmission mode near-field microscopy. Various dielectric materials of different topographies have been studied to develop an understanding of normal and anomalous contrast modes mainly characterized by topographically induced contrast.

The refractive index profile of a straight channel phosphosilicate glass planar optical waveguide is obtained with high spatial resolution (approximately 0.25 micrometers ) using near- field scanning optical microscopy (NSOM). The optical intensity profile of the waveguide mode is measured by NSOM and the refractive index distribution is calculated from the measured intensity. The calculated refractive index distribution is in agreement with that expected from the fabrication procedure and provides evidence for phosphorous diffusion between the core and cladding regions.

A `stand-alone' Photon Scanning Tunneling Microscope combined with an Atomic force Microscope, using a micro-fabricated silicon-nitride probe, is applied to the imaging of field distribution in integrated optical ridge waveguides. The electric field on the waveguide is locally probed by coupling to the evanescent wave. Application to direct observation of TM and TE modal field distributions, both in lateral and vertical direction, mode beating between low and higher order modes, and behavior of a Y-junction wavelength (de)multiplexer is demonstrated.

Near field microscopy has been used to investigate the guided mode intensity distribution in a variety of optical channel waveguide structures. We have studied the optical field intensity distribution in channel waveguides, directional couplers, and Y-branches above the surface of the structures scanning transverse to the waveguide propagation direction. Single mode channel waveguides are formed by etching a ridge in Si₃N₄/SiO₂ structures and excited at a wavelength of 833 nm. Measurements of the intensity distribution transverse to a channel waveguide reveal a cosine squared variation of intensity above the ridge region and an exponential decay away from the ridge region, in agreement with theoretical expectations. For more complicated structures, for instance the directional coupler, measurements along the two waveguides of the coupler provide a detailed view of optical power transfer from one waveguide to the other. Measurements also provide a detailed view of the evolution of the optical power in the Y-junction.

In this paper we present a simplified but general theoretical model of the interaction of a near- field probe with evanescent fields. The predicted behavior exhibits some interesting features. We also describe an experiment to test these models and report our first results.

To determine the feasibility of coupling the output of a single-mode optical fiber into a single- mode rib waveguide in a temperature varying environment, a theoretical calculation of the coupling efficiency between the two was investigated. Due to the complex geometry of the rib guide, there is no analytical solution to the wave equation for the guided modes, thus, approximation and/or numerical techniques must be utilized to determine the field patterns of the guide. In this study, three solution methods were used for both the fiber and rib guide fields; the effective-index method, Marcatili's approximation, and a Fourier method. These methods were utilized independently to calculate the electric field profile of each component at two temperatures, 20 degree(s)C and 300 degree(s)C, representing a nominal and high temperature. Using the electric field profile calculated from each method, the theoretical coupling efficiency between an elliptical-core optical fiber and a rib waveguide was calculated using the overlap integral and the results were compared. It was determined that a high coupling efficiency can be achieved when the two components were aligned. The coupling efficiency was more sensitive to alignment offsets in the y direction than the x, due to the elliptical modal field profile of both components. Changes in the coupling efficiency over temperature were found to be minimal.

Scanning near-field optical microscopy has been used to study birefringent banded polymer spherulites. The bands and their sub-structure is seen to correlate directly with the topography verifying established spherulite morphology theories. Block co-polymer examination of a poly(styrene)-poly(2-vinyl pyridine) have revealed sharp contrast for dielectric structures. This contrast is thought to be due to topographic diffraction effects. Ring like structures seen in some of the near-field images are thought to correspond to the accepted structure of this polymer.