bluuebunny/crossref_metadata_2025_split huggingface dataset:
Probing highly confined optical fields in the focal region of a high NA parabolic mirror with subwavelength spatial resolution
Authors: Debus C. , Lieb M. A. , Drechsler A. , Meixner A. J. 
Published: June 2003

SummaryParabolic mirrors with a high numerical aperture can be conveniently used to produce highly confined optical fields in the focal region. Furthermore, these fields can have interesting polarization behaviour due to the high numerical aperture. In particular, if the mirror is illuminated with a size matched radially polarized or azimuthally polarized doughnut mode, the electric field has in the focal region almost exclusively a longitudinal or a transverse polarization component. Such field distributions are interesting for applications in confocal or near‐field optical microscopy. Here we present experimental results where we have probed some of these field distributions by raster scanning a fine gold tip in nanometer steps through the focal region and detecting the scattered light intensity. The measured intensity patterns are compared with corresponding vector‐field calculations.
Plasmon‐coupled tip‐enhanced near‐field optical microscopy
Authors: Bouhelier A. , Renger J. , Beversluis M. R. , Novotny L. 
Published: June 2003

SummaryNear the cut‐off radius of a guided waveguide mode of a metal‐coated glass fibre tip it is possible to couple radiation to surface plasmons propagating on the outside surface of the metal coating. These surface plasmons converge toward the apex of the tip and interfere constructively for particular polarization states of the initial waveguide mode. Calculations show that a radially polarized waveguide mode can create a strong field enhancement localized at the apex of the tip. The highly localized enhanced field forms a nanoscale optical near‐field source.
Current‐sensing scanning near‐field optical microscopy using a metal probe for nanometre‐scale observation of electrochromic films
Authors: Iwata F. , Mikage K. , Sakaguchi H. , Kitao M. , Sasaki A. 
Published: June 2003

SummaryA novel technique for scanning near‐field optical microscopy capable of point‐contact current‐sensing was developed in order to investigate the nanometre‐scale optical and electrical properties of electrochromic materials. An apertureless bent‐metal probe was fabricated in order to detect optical and current signals at a local point on the electrochromic films. The near‐field optical properties could be observed using the local field enhancement effect generated at the edge of the metal probe under p‐polarized laser illumination. With regard to electrical properties, current signal could be detected with the metal probe connected to a high‐sensitive current amplifier. Using the current‐sensing scanning near‐field optical microscopy, the surface topography, optical and current images of coloured WO3 thin films were observed simultaneously. Furthermore, nanometre‐scale electrochromic modification of local bleaching could be performed using the current‐sensing scanning near‐field optical microscopy. The current‐sensing scanning near‐field optical microscopy has potential use in various fields of nanometre‐scale optoelectronics.
Excitation dynamics in a three‐quantum dot system driven by optical near‐field interaction: towards a nanometric photonic device
Authors: Kobayashi K. , Sangu S. , Shojiguchi A. , Kawazoe T. , Kitahara K. , Ohtsu M. 
Published: June 2003

SummaryUsing density operator formalism, we discuss interdot excitation energy transfer dynamics driven by the optical near‐field and phonon bath reservoir, as well as coherent excitation dynamics of a quantum dot system. As an effective interaction between quantum dots induced by the optical near‐field, the projection operator method gives a renormalized dipole interaction, which is expressed as a sum of the Yukawa functions and is used as the optical near‐field coupling of quantum dots. We examine one‐ and two‐exciton dynamics of a three‐quantum dot system suggesting a nanometric photonic switch, and numerically obtain a transfer time comparable with the recent experimental results for CuCl quantum dots.
Large‐area topography analysis and near‐field Raman spectroscopy using bent fibre probes
Authors: Prikulis J. , Murty K. V. G. K. , Olin H. , Käll M. 
Published: June 2003

SummaryWe present a method for combined far‐field Raman imaging, topography analysis and near‐field spectroscopy. Surface‐enhanced Raman spectra of Rhodamine 6G (R6G) deposited on silver nanoparticles were recorded using a bent fibre aperture‐type near‐field scanning optical microscope (NSOM) operated in illumination mode. Special measures were taken to enable optical normal‐force detection for control of the tip–sample distance. Comparisons between far‐field Raman images of R6G‐covered Ag particle aggregates with topographic images recorded using atomic force microscopy (AFM) indicate saturation effects due to resonance excitation.
Scanning near‐field optical microscopy using semiconductor nanocrystals as a local fluorescence and fluorescence resonance energy transfer source
Authors: Shubeita G. T. , Sekatskii S. K. , Dietler G. , Potapova I. , Mews A. , Basché T. 
Published: June 2003

SummaryLocal fluorescence probes based on CdSe semiconductor nanocrystals were prepared and tested by recording scanning near‐field optical microscopy (SNOM) images of calibration samples and fluorescence resonance energy transfer SNOM (FRET SNOM) images of acceptor dye molecules inhomogeneously deposited onto a glass substrate. Thousands of nanocrystals contribute to the signal when this probe is used as a local fluorescence source while only tens of those (the most apical) are involved in imaging for the FRET SNOM operation mode. The dip‐coating method used to make the probe enables diminishing the number of active fluorescent nanocrystals easily. Prospects to realize FRET SNOM based on a single fluorescence centre using such an approach are briefly described.
Near‐field radiation of bow‐tie antennas and apertures at optical frequencies
Authors: Şendur K. , Challener W. 
Published: June 2003

SummaryWe investigate the ability of the bow‐tie slot antenna to generate intense optical spots below the diffraction limit. A commercially available finite‐difference time‐domain electromagnetic modelling software is used in the numerical simulations. The finite‐difference time‐domain software is first compared to analytical results at optical frequencies to verify its accuracy. We then present numerical simulations for various geometries involving apertures on thin films and the bow‐tie antenna. The transmission efficiency and optical spot size of the bow‐tie antenna are compared with those of rectangular and circular apertures on thin metal films. We also investigate the effects of material composition, frequency, and antenna geometry on the near‐field radiation pattern using numerical simulations.
Scanning near‐field optical microscopy of a cell membrane in liquid
Authors: Höppener C. , Molenda D. , Fuchs H. , Naber A. 
Published: June 2003

SummaryThe applications of scanning near‐field optical microscopy to biological specimens under physiological conditions have so far been very rare since common techniques for a probe–sample distance control are not as well suited for operation in liquid as under ambient conditions. We have shown previously that our own approach for a distance control, based on a short aperture fibre probe and a tuning fork as force sensor in a tapping mode, works well even on soft material in water. By means of an electronic self‐excitation circuit, which compensates for changes of the resonance frequency due to evaporation of liquid, the stability of the force feedback has now been further improved. We present further evidence for the excellent suitability of the tapping‐mode‐like distance control to an operation in liquid, for example, by force‐imaging of double‐stranded DNA. Moreover, we demonstrate that a nuclear envelope in liquid can be imaged with a high optical resolution of ∼70 nm without affecting its structural integrity. Thereby, single nuclear pores in the nuclear envelope with a nearest neighbour distance of ∼120 nm have been optically resolved for the first time.
A versatile multipurpose scanning probe microscope
Authors: Cefalì E. , Patanè S. , Gucciardi P. G. , Labardi M. , Allegrini M. 
Published: June 2003

SummaryA combined scanning probe microscope has been developed that allows simultaneous operation as a non‐contact/tapping mode atomic force microscope, a scattering near‐field optical microscope, and a scanning tunnelling microscope on conductive samples. The instrument is based on a commercial optical microscope. It operates with etched tungsten tips and exploits a tuning fork detection system for tip/sample distance control. The system has been tested on a p‐doped silicon substrate with aluminium depositions, being able to discriminate the two materials by the electrical and optical images with a lateral resolution of 130 nm.
Study of the focused laser spots generated by various polarized laser beam conditions
Authors: Fu Y. H. , Ho F. H. , Lin W. C. , Liu W.‐C. , Tsai D. P. 
Published: June 2003

SummaryIn this work, three‐dimensional near‐field imaging of the focused laser spot was studied theoretically and experimentally. In the theoretical simulation, we use the electromagnetic equivalent of the vectorial Kirchhoff diffraction integral to calculate the intensity distribution of the focal region, and a high depolarization is found in high numerical aperture systems (NA = 0.85). The experimental set‐up is based on a near‐field scanning optical microscope (NSOM) system. A high‐NA objective lens is used to focus incident light of various polarizations, and a tapered near‐field optical fibre probe of the NSOM system is used to determine the intensity of the focal field. The results show an asymmetric distribution of the focused intensity with the linear polarized laser beam.
Simulation of an aperture in the thick metallic screen that gives high intensity and small spot size using surface plasmon polariton
Authors: Tanaka K. , Tanaka M. 
Published: June 2003

SummaryThe optical wave behaviour around a subwavelength aperture in a thick metallic screen is examined through three‐dimensional computer simulation. Treating the metallic screen as a dielectric slab with complex‐valued permittivity, it is possible to design an aperture that simultaneously provides high intensity and small spot size through the excitation of surface plasmon polaritons on the side walls of the aperture.
Transient optical elements: application to near‐field microscopy
Authors: Simanovskii D. , Palanker D. , Cohn K. , Smith T. 
Published: June 2003

SummaryWe report methods of near‐field infrared microscopy with transient optically induced probes. The first technique – a transient aperture (TA) – uses photoinduced reflectivity in semiconductors to generate a relatively large transient mirror (TM) with a small aperture at its centre. We report the optical properties of the TM and TA and experiments performed on near‐field imaging with the TA. The second technique is based on solid immersion microscopy, in which high resolution is achieved when light is focused inside a solid with a high refractive index. By creating a transient Fresnel lens on the surface of a semiconductor wafer via photoinduction, we were able to form a solid immersion lens (SIL) for use as a near‐field probe. The use of transient probes eliminates the need for mechanical scanning of the lens or sample, and thus provides a much faster scanning rate and the possibility to work with soft and liquid objects.
Photo‐initiated energy transfer in nanostructured complexes observed by near‐field optical microscopy
Authors: Wurtz G. A. , Hranisavljevic J. , Wiederrecht G. P. 
Published: June 2003

SummaryWe report an apertureless near‐field optical study on nanostructured objects formed by J‐aggregates adsorbed on silver (Ag) nanoparticles. Near‐field images reveal that the enhanced near‐field from the dressed particle's (DP) resonantly excited plasmon oscillation is efficiently absorbed by the J‐aggregates. The sensitivity of the near‐field images recorded at the harmonics of the probe vibration frequency suggests that the DP is releasing part of the absorbed energy radiatively upon interaction with the probe. The role of the probe in providing this new radiative relaxation channel is further confirmed as fluorescence from the J‐aggregates on the particle is detected on the particle location only. We based the interpretation of our results on the near‐field optical response from a bare Ag particle excited at the plasmon resonance as well as on far‐field emission and transient absorption experiments.
How light gets through periodically nanostructured metal films: a role of surface polaritonic crystals
Authors: Zayats A. V. , Salomon L. , De Fornel F. 
Published: June 2003

SummaryThe physical origin of the enhanced optical transmission of periodically structured films related to surface plasmon polaritons is discussed from first principles. The enhancement of transmission through smooth, randomly rough and periodically nanostructured films is considered. Analysis shows that any metal (or dielectric) nanostructured film can exhibit enhanced transmission in certain spectral ranges corresponding to surface plasmon (or phonon) polariton Bloch mode states on a periodic structure. Resonant tunnelling via these states is responsible for the transmission enhancement. The properties of surface polaritonic crystals are analogous to those of photonic crystals and can find numerous applications for scaling down optical devices to nanometric dimensions as well as for designing novel nanostructured materials whose optical properties are determined by surface polariton interaction in a periodic structure.
Bessel beams as virtual tips for near‐field optics
Authors: Grosjean T. , Courjon D. , Van Labeke D. 
Published: June 2003

SummaryIn the previous NFO meeting, we proposed the use of confined evanescent light beams as ‘virtual’ or ‘immaterial’ tips. Unfortunately, this technique was hindered by the need for perfectly radially polarized light beams. In this communication, we propose a simple, stable and cheap method allowing the generation of beams of any polarization and more especially of purely radially polarized light beams. We also demonstrate both theoretically and experimentally that for near‐field imaging systems polarization is a limiting factor of resolution and light confinement. Finally, we present the very first experimental results dealing with virtual tips.
Performance of visible and mid‐infrared scattering‐type near‐field optical microscopes
Authors: Taubner T. , Hillenbrand R. , Keilmann F. 
Published: June 2003

SummaryWe describe the principles of two scattering‐type near‐field optical microscopes (s‐SNOMs), one operating at 633 nm wavelength, the other at selectable wavelengths in the range 7.3–11.3 µm, and compare the measurement experience. Both use interferometric detection of scattered radiation, and are therefore capable of amplitude and phase‐contrast imaging. In this study both instruments use the same or even identical commercial probe tips, and measure a single, three‐component, test sample. Our results show that the imaging process of s‐SNOM is wavelength‐independent, namely, that the resolution is determined by the properties of the tip only, and that the contrast is given by the complex refractive index of the sample, predictable from a simple, analytical model of tip–sample interaction. A novel, ‘edge‐darkening’ artefact is described which may appear in s‐SNOM and that is wavelength‐independent.
Experimental studies of surface plasmon polariton band gap effect
Authors: Volkov V. S. , Bozhevolnyi S. I. , Leosson K. , Boltasseva A. 
Published: June 2003

SummarySurface plasmon polaritons (SPPs) propagation at a gold film surface covered by periodic arrays of ∼40‐nm‐high scatterers arranged in a triangular lattice of different periods containing straight line defects is studied using collection scanning near‐field optical microscopy. The results reveal the dependence of the SPP band gap (SPPBG) effect manifested via the SPP reflection and guiding (along line defects) on the parameters of the surface structures (period, filling factor and lattice orientation). We find that the SPPBG effect is stronger along ΓK direction for all investigated periodic structures. Our results demonstrate that the SPPBG effect becomes less pronounced with a decrease of the filling factor and disappears for a filling factor close to 0.2. We also observe that the centre of the SPPBG shifts towards longer wavelengths with an increase of the lattice period.
Visual discrimination by the honeybee (Apis mellifera): the position of the common centre as the cue
Authors: Horridge Adrian 
Published: June 2003

Abstract. Bees can be trained to discriminate between a target with a 20° spot above a 10° spot of the same colour, and another target with the spots exchanged in position. Tests show that they do not remember the separate positions of spots of the same colour (including black) on the same target. The bees discriminate the difference in positions, in the vertical direction, of the common centres of the spots taken together, with or without green contrast.Similar results are obtained in discriminations of a fixed T shape, each composed of two broad black bars subtending 8 by 24°, vs the same shape inverted. The trained bees fail to discriminate between the T shapes when the centroids are at the same level in the vertical direction. Moving the shapes in the horizontal direction in tests has less effect. Quite different results are obtained when the two bars of the T shape differ in colour. The bees discriminate the positions of the two colours separately, but they still fail to discriminate the shape of the T. The results can be explained by filters that detect the intensities within their fields, irrespective of shape, and weigh them according to their vertical angles from the horizontal midline. The normal function of these filters could be to detect the levels of objects relative to the horizon when the bee is in flight.
Predicting epidemics of yellow rust (Puccinia striiformis) on the upper canopy of wheat from disease observations on lower leaves
Authors: Young C. S. , Paveley N. D. , Vaughan T. B. , Thomas J. M. , Lockley K. D. 
Published: June 2003

Data from field experiments were used to test whether disease observations on lower leaves of wheat were good predictors of future epidemic development in the upper canopy. Fungicide treatments to replicated plots in 1994 and 1995 caused variation in levels of initial inoculum of urediniospores of yellow rust (Puccinia striiformis). Observations of symptom severity were made on individual leaf layers throughout the season. Sporulating lesions on lower leaves were considered to be a measure of inoculum source strength for transfer to upper culm leaves. Low source strengths were associated with delays in epidemic development on the upper leaves, as quantified by a location parameter, tm, the time at which severity reached half of the asymptote value in logistic fits to disease progress data on the upper leaves. However, there was much unexplained variation, probably due to extraneous variation in upward transfer efficiency of inoculum and rates of epidemic development. Vanderplank's sanitation ratio theory was used to account for variation in inoculum transfer and epidemic rate. The analysis revealed that if the aim is to predict disease on a newly emerged culm leaf, during the period when it can be treated effectively with fungicide, then observations of disease two leaves further down the culm were of the greatest predictive value (R2 = 86%). These observations, however, need to be integrated with information about factors affecting upward inoculum transfer and rates of epidemic development if acceptable predictive precision is to be achieved.
Tomato leaf curl geminivirus in Australia: occurrence, detection, sequence diversity and host range
Authors: Stonor J. , Hart P. , Gunther M. , DeBarro P. , Rezaian M. A. 
Published: June 2003

The occurrence of whitefly transmitted geminiviruses in Australia was studied using a mixed DNA probe capable of detecting a range of distinct geminiviruses. The only geminivirus species detected was Tomato leaf curl virus (TLCV), which is spread across a vast geographical region of far‐northern coastal Australia, an area inhabited by the Australasian‐Oceania biotype of Bemisia tabaci. The newly introduced silverleaf whitefly, B. tabaci biotype B, forms high population densities in the eastern coastal region of Queensland and is currently located approximately 150 km from the nearest known TLCV‐infected area. The viral host range appeared to be narrow and of 58 species of crop plants and weeds inoculated using the B biotype, only 11 became infected with the virus, including five that did not show foliar symptoms. A DNA fragment of 694 nt, including the complete C4 open reading frame (ORF), the overlapping N‐terminal part of the C1 ORF and the viral iterons involved in replication, was amplified from 11 TLCV field isolates and sequenced. Sequence analysis revealed an overall sequence variation of up to 14% in this region, as well as the presence of distinct viral iterons.
Nematicidal activity of essential oils and organic amendments from Asteraceae against root‐knot nematodes
Authors: Pérez M. P. , Navas‐Cortés J. A. , Pascual‐Villalobos M. J. , Castillo P. 
Published: June 2003

The essential oil of Chrysanthemum coronarium flowerheads showed strong nematicidal activity in vitro and in growth‐chamber experiments. Essential oil concentrations of 2, 4, 8 and 16 µL mL−1, significantly reduced hatch, J2 survival (determined by final value and area under curves of cumulative percentage hatch or mortality) and reproduction rate of Meloidogyne artiellia in vitro, with the lowest values occurring at 16 µL mL−1. In pot trials with chickpea cv. PV 61, essential oil concentrations of 10–40 µL per 500 cm3 soil, applied on sterile cotton pellets, also significantly reduced the nematode's reproduction rate. The biological processes of mortality and hatching/reproduction were adequately described by the monomolecular and expanded negative exponential models, respectively. Effectiveness of soil amendment with either flowers, leaves, roots or seeds of C. coronarium, and flowers from several species of Asteraceae (Chrysanthemum segetum, Calendula maritima, Calendula officinalis and Calendula suffruticosa) at 5 g per 500 cm3 soil was tested for suppression of M. artiellia and growth of chickpea cv. PV 61 under growth‐chamber conditions. In these tests, flowers of all five Asteraceae species and various parts of C. coronarium significantly reduced reproduction rates of M. artiellia, by 83·0–95·9%, with the minimum rates occurring in infected chickpea plants amended with flowers of C. officinalis and C. suffruticosa. The in vitro and in planta results suggest that the essential oil of C. coronarium and organic amendments from Asteraceae species may serve as nematicides.