Two evanescent fields were generated on prism surface by incidence of two laser beams from opposite side of the prism at total internal reflection angle. Using photon force of these two evanescent fields, a small particle can be moved backward and forward, and trapped on prism surface. The experimental result shows that a latex sphere of radius 10micrometers can be moved automatically between two points with an error of 9 micrometers . Trapping experiment also shows a clear effect on keeping the position of a small particle against the Brownian motion and flow of water.

Recent developments in genetic engineering and medical informatics offer enormous potential for biotechnology. However, key enabling technologies, such as medical instrumentation and analytical tools, are required to support further research in this field. The scanning near-field optical microscopy (SNOM) is one of the key instruments for research in these areas. In this paper, we review the synergy of the SNOM with other technologies for the imaging and characterization of biological materials. Based on this review, the components and systems design parameters are summarized.

In this work the dynamics of laser excited electrons in elliptic shaped silver nanoparticles were studied by means of the time-resolved two-photon-photoemission technique. The shape of the nanoparticles allows to distinguish between particle plasmon excitation and electron-hole pair excitation (intraband process) by simply changing the polarization of the laser pulse. These comparative studies, using the same experimental apparatus, enable us to study the respective role of collective and quasi-particle excitation in the electron dynamics of a metallic nanoparticle. The results are analyzed with a three level model according to the Liouville-von Neumann equation. The first measurements indicate that the electron dynamics vary considerably between these two excitation cases.

We investigate the possibility of using arrays of closely spaced metal nanoparticles as waveguides for electromagnetic energy below the diffraction limit of visible light. Coupling between adjacent particles sets up coupled plasmon modes that give rise to coherent propagation of energy along the array. A point dipole analysis predicts group velocities of energy transport that exceed 0.1c along straight arrays and shows that energy transmission through chain networks such as corners and tee structures is possible at high efficiencies. Although radiation losses into the far field are negligible due to the near-field nature of the coupling, resistive heating leads to transmission losses of about 3 dB/500 nm for gold and silver particles. We confirmed the predictions of this analytical model using numeric finite difference time domain (FDTD) simulations. Also, we have fabricated gold nanoparticle arrays using electron beam lithography to study this type of electromagnetic energy transport. A modified illumination near field scanning optical microscope (NSOM) was used as a local excitation source of a nanoparticle in these arrays. Transport is studied by imaging the fluorescence of dye-filled latex beads positioned next to the nanoparticle arrays. We report on initial experiments of this kind.

The fluorescence blinking of single CdSe/ZnS nanocrystals under different experimental conditions is investigated. We show that the blinking process is very sensitive to the particle environment even if the nanocrystals are covered with a few monolayers of ZnS. Especially the presence of oxygen leads to a shortening of the on-times but leaves the off-times almost unaffected. Therefore, oxygen which is adsorbed to the surface might act as a scavenger for photo generated electrons and leaves the particle in its (positively charged) dark state.

Nanoparticles (clusters) of type II-VI semiconductor materials (CdS, CdSe, CdTe) have been prepared with average diameters between 1 nm and 25 nm using precipitation methods in aqueous or organic solutions and deposited on oxidic substrates. The intrinsic electronic structure of these particles with sizes around the excitonic Bohr radius of the respective materials has been investigated by a combination of optical spectroscopy methods including reflection/transmission measurements, photoluminescence, Raman spectroscopy, absorption saturation and second harmonic generation (SHG) measurements. Together with supporting information on the morphology and the arrangement of the particles obtained from Transmission Electron Microscopy (TEM), Scanning Probe Microscopy and X-Ray diffraction we were able to determine the size dependence of excitonic excitations within the clusters, following in good agreement theoretical predictions derived from quantum mechanical, extended particle-in-a-box models.

Perylene- and phthalocyanine- pigment molecules were systematically modified and consequences were studied for their solid state properties. Thin films (1 - 150 nm) were prepared by physical vapor deposition. Intermolecular interactions were probed by optical measurements in absorption and emission. Atomic force microscopy served to analyze the morphology of films. Different interactions among the molecules and with the substrate surfaces allowed to prepare either crystalline or amorphous films. Crystalline films of perylene pigments were typically characterized by strong chromophore coupling leading to a characteristic splitting, well- defined shifts of the optical absorption bands and emission mainly from excimer species whereas the chromophore coupling in amorphous films was suppressed sufficiently to provide a significantly increased optical emission yield from uncoupled monomer states. Temperature-dependent optical emission experiments are presented which allow a detailed discussion of monomer vs. excimer emission. Decoupling of the chromophores could be obtained by appropriate chemical substitutions at the aromatic core system of phthalocyanines and perylene pigments that led to strong deviations from planarity. This was achieved by the introduction of bulky substituents in the bay position of the aromatic perylene core and by changes in the coordination number of the central group in phthalocyanines. The strategy led to a strongly enhanced optical emission for both classes of materials. This could be obtained, however, either in an amorphous arrangement of the molecules or under conservation of crystallinity, both offering alternative advantages.

Molecular sieves, such as nanoporous AlPO₄-5, can host a wide variety of laser-active dyes. Slim dyes like Coumarin40 or Oxazine 1, fitting into the channel pores, as well as bulky dyes like rhodamines and Oxazine 750, being located in defect sites of the molecular sieve structure, are embedded during microwave-assisted crystallization. The fast microwave-assisted crystallization offers a new procedure for the stable and monomeric encapsulation of organic dyes into molecular sieves without any degradation of the chromophores and enables the control of the morphology of the host material. Based on this class of materials a new form of microlasers has been created. Their properties depend on size and shape of the molecular sieve crystals. The microcrystals act as hexagonal ring resonators (whispering gallery mode). In dependence on the morphology of the crystals different laser properties have been observed in agreement with theoretical predictions. Large hexagonal crystals (diameter of the hexagonal plane > 7 micrometers ) revealed multiline laser emission, while smaller crystals (diameter about 5 micrometers ) oscillate on one single line. The laser threshold power density decreases with decreasing diameter of the crystals. In terms of pumping needed to reach lasing molecular sieve microlasers are comparable to quantum dot semiconductor lasers.

An electromagnetic field is characterized by an amplitude, a phase and a polarization state. In this paper, we intend to gain an understanding of the interaction of light with microstructures in order to determine their optical properties. Measurements of the amplitude and phase close to gratings are presented using a heterodyne scanning probe microscope. We discuss some basic properties of phase distributions. Indeed, coherent light diffracted by microstructures can give birth to phase dislocations, also called phase singularities. Phase singularities are isolated points where the amplitude of the field is zero. The position of these special points can lead us to information about the structure (shape, surface defects, etc), by comparing with rigorous diffraction calculation using e.g. the Fourier Modal Method (FMM). We present high-resolution measurements of such phase singularities and compare them with theoretical results. Polarization effects have been studied in order to understand the field conversion by the fiber tip.

The scattered electromagnetic near fields due to fluctuations in the surface height and/or lateral variations in the electromagnetic medium parameters are evaluated using a full wave approach. Since the scales of the height and medium fluctuations considered could be significantly smaller or larger than the electromagnetic wavelengths, the familiar perturbation and physical/geometrical optics solutions cannot be used nor is it possible to investigate sub-wavelength features based on far-field measurements. The full wave approach employs complete field expansion that include propagating and evanescent waves as well as lateral waves and surface waves. The lateral waves and surface waves are not accounted for in the perturbation and physical optics solutions. Unlike the physical optics and small perturbation approach, exact boundary conditions for the electric and magnetic fields are imposed at the rough interfaces. For irregular layered media the complete field expansions are associated with propagating and evanescent waves, the lateral wave term and surfaces waves guided by the stratified structure. The interfaces between the irregular stratified structures are not characterized by the approximate impedance boundary conditions. The modal expansions while complete, do not individually satisfy the correct boundary conditions, and they do not uniformly coverage the irregular boundaries, therefore term by term differentiation of the field expansions is avoided.

Non-intrusive laser-spectroscopical methods for the diagnostics of the gas-surface interaction in the near-field of a dielectric surface have been developed both experimentally and theoretically. The techniques base on either two-photon evanescent wave excitation or combined evanescent-volume wave excitation. Spectra obtained for sodium atoms at a glass-vacuum interface are quantitatively reproduced by a rigorous theoretical approach. In the case of pure evanescent wave excitation the excitation conditions can be chosen such that either the velocity distribution of desorbing atoms is determined or that atom-surface interaction parameters (polarizability of the adsorbed atoms, desorption rate, sticking coefficient) are obtained from the Autler- Townes splitting of the two-photon lines. By the use of combined evanescent-volume wave excitation one is able to distinguish optically between different groups of atoms interacting with the surface and one can extract their two- dimensional velocity distributions. In addition, information is obtained about superelastic scattering of the atoms interacting with the dielectric substrate.

The ability to characterize the sub-surface mechanical properties of a bulk or thin film material at the sub-micron level has applications in the microelectronics and thin film industries. In the microelectronics industry, with the decrease of line widths and the increase of component densities, sub-surface voids have become increasingly detrimental. Any voids along an integrated circuit (IC) line can lead to improper electrical connections between components and can cause failure of the device. In the thin film industry, the detection of impurities is also important. Any impurities can detract from the film's desired optical, electrical, or mechanical properties. Just as important as the detection of voids and impurities, is the measurement of the elastic properties of a material on the nanometer scale. These elastic measurements provide insight into the microstructural properties of the material. We have been investigating a technique that couples the high-resolution surface imaging capabilities of the apertureless near-field scanning optical microscope (ANSOM) with the sub-surface characterization strengths of high-frequency ultrasound. As an ultrasonic wave propagates, the amplitude decreases due to geometrical spreading, attenuation from absorption, and scattering from discontinuities. Measurement of wave speeds and attenuation provides the information needed to quantify the bulk or surface properties of a material. The arrival of an ultrasonic wave at or along the surface of a material is accompanied with a small surface displacement. Conventional methods for the ultrasound detection rely on either a contact transducer or optical technique (interferometric, beam deflection, etc.). However, each of these methods is limited by the spatial resolution dictated by the detection footprint. As the footprint size increases, variations across the ultrasonic wavefront are effectively averaged, masking the presence of any nanometer-scale sub-surface or surface mechanical property variations. The use of an ANSOM for sensing ultrasonic wave arrivals reduces the detection footprint allowing any nanometer scale variations in the microstructure of a material to be detected. In an ANSOM, the ultrasonic displacement is manifested as perturbations on the near-field signal due to the small variations in the tip-sample caused by the wave arrival. Due to the linear dependence of the near-field signal on tip-sample separation, these perturbations can be interpreted using methods identical to those for conventional ultrasonic techniques. In this paper, we report results using both contact transducer (5 MHz) and laser-generated ultrasound.

An approach to the optical investigation of probes for scanning near-field optical microscopes (SNOM tips) and recognition of their near-field parameters by far-field measurements is considered. The comparison of approximate calculations of vector light field diffracted by a subwavelength aperture with more rigorous calculations of the light field passing through tapered end of a SNOM tip is presented. A numerical iterative procedure of the SNOM tip aperture reconstruction by the analytical continuation of the emerging light Fourier spectrum is presented. The approach is based on the use of plane waves covering a wide range of spatial frequencies. The results of experimental measurements and far-field data treatment with the definition of a subwavelength aperture are discussed.

We suggest two methods attaching tip to the quartz crystal resonator to be applied to a near-field optical scanning microscope probe. High-speed near-field scanning optical microscopy images obtained with the quartz crystal resonator probe are presented. We have achieved fast scanning imaging at the scanning speed of 1.3 mm/s without any compromise of spatial lateral resolution. Applying a concept of the acoustic wave, the topographic image of soft sample with the quartz crystal resonator probe is interpreted.

We report on the application as well as microfabrication process of batch-fabricated optical near-field sensors using cantilevered scanning force microscopy tips. The process includes implementation of a coaxial conductive geometry into a silicon sensor tip, along with electrical connections on the cantilever and chip body. The coaxial guide structure is used as electric lead to a sub-micron Schottky photodetector at the end of the tip, formed at the junction of the protruding silicon core and a recessed aluminum coating. The I-V curves of these sensors are consistent with numerical studies for such constricted geometries. Optical near-field data gathered by this sensor in topography-following mode is presented.