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At least 631 records · Page 35Linked to original sources
PubMed1999

Orientation topography of layer 4 lateral networks revealed by optical imaging in cat visual cortex (area 18).

The functional specificity of corticocortical connections with respect to the topography of orientation selectivity was studied by optical imaging of intrinsic signals and bulk injections of fluorescent latex beads (green and red) and biocytin into layer 4. The distributions of retrogradely labelled cells and anterogradely labelled axon terminals were histologically reconstructed from all cortical laminae, and the resulting anatomical maps compared with the optically imaged functional maps. Layer 4 injections produced extensive horizontal labelling up to 2-3 mm from the injection centres albeit without the clear patchy pattern described after layer 2/3 injections (Gilbert & Wiesel 1989, J. Neurosci., 9, 2432-2442; Kisvárday et al. 1997, Cerebral Cortex, 7, 605-618). The functional (orientation) distribution of the labelled projections was analysed according to laminar location and lateral spread. With regard to the former, no major difference in the orientation topography between supragranular- (upper tier), granular- (middle tier) and infragranular (lower tier) layers was seen. Laterally, proximal and distal projections were distinguished and further dissected into three orientation categories, iso- (+/- 30 degrees ), oblique- (+/- 30-60 degrees ) and cross-orientations (+/- 60-90 degrees ) with respect to the orientation preference at the injection sites. The majority of distal connections (retrograde and anterograde) was equally distributed across orientations (35.4% iso-, 33.7% oblique-, and 30.9% cross-orientations) that are equivalent with a preponderance to dissimilar orientations (oblique- and cross-orientations, 64.6%). In one case, distal excitatory and inhibitory connections could be morphologically distinguished. For both categories, a marked bias to dissimilar orientations was found (excitatory, 63.7%; inhibitory, 86.6%). Taken together, these results suggest that the long-range layer 4 circuitry has a different functional role from that of the iso-orientation biased (52.9%, Kisvárday et al. 1997, Cerebral Cortex, 7, 605-618) layer 2/3 circuitry, and is perhaps involved in feature difference-based mechanisms, e.g. figure ground segregation.

Animals↗
PubMed2003

Correlation analysis of visual field thresholds and scanning laser ophthalmoscopic optic nerve head measurements in glaucoma.

In a cross-sectional study of 50 consecutive primary open-angle glaucoma cases, full threshold 30-2 visual fields on Humphrey Visual Field Analyser were correlated to stereometric parameters obtained using a scanning laser ophthalmoscope (HRT II). The strength of linear correlation between the stereometric parameters and visual thresholds was used to generate a correspondence map between the optic disc and the visual field. Rim/disc area ratio and cup/disc area ratio correlated with the visual thresholds at the highest number of points in the visual fields. Thresholds at superior hemifield locations correlated best with the rim/disc area ratio and cup/disc area ratio in the inferonasal sector and the ones in the inferior hemifield correlated best with the rim/disc area ratio and cup/disc area ratio in the superotemporal sector. Optic disc parameters correlated better with inferior field locations and non-edge points than superior field locations and edge points. The data indicate that rim/disc area ratio and cup/disc area ratio measurements on HRT II have a good correlation with visual field damage seen on automated visual fields.

Adult↗
PubMedDate not supplied

Retinal thickness assessed by optical coherence tomography (OCT) in pseudophakic macular edema.

PURPOSE: To evaluate the usefulness of the optical coherence tomography (OCT) retinal map in angiographic pseudophakic macular edema (ACME). METHODS: This is a prospective analysis of a group of 36 pseudophakic eyes at the fifth postoperative week, submitted to optical coherence tomography 2 macular map and fluorescein angiography on the same day and, a control group of twenty-two 20/20 vision eyes with a minimum 6-month postoperative period, submitted to optical coherence tomography 2 macular map only. Exclusion criteria were diabetes, any macular pathology and unreadable optical coherence tomography or angiogram. The angiograms were divided into three groups according to the edema intensity: Group I: level 0 (absence of angiographic pseudophakic macular edema); group II: levels 1 and 2 (incomplete and complete perifoveal angiographic pseudophakic macular edema respectively) and group III: levels 3 and 4 (up to one disc diameter and greater than one disc diameter angiographic pseudophakic macular edema area respectively). The nine zones of the optical coherence tomography macular map were compared between the control and the three subgroups of the study group and, between group I and groups II and III. RESULTS: Among the 36 eyes, 23 (64%) were classified as group I, 10 (28%) as group II and three (8%) as group III. The mean thickness of the fovea zone was 185+/-15 microm for the control group, 189+/-24 microm for group I, 213+/-33 microm for group II and 455+/-38 microm for group III. Significant differences: between group III and the control or group I for all zones (p<0.01) and, between group II and control or group I for the fovea and temporal inner zones (p<0.05). CONCLUSION: The optical coherence tomography retinal map is useful in angiographic pseudophakic macular edema diagnosis.

Adult↗
PubMed1975

Factors determining decussation at the optic chiasma by developing retinotectal fibres in Xenopus.

In Amphibia all primary retinotectal nerve fibres cross at the chiasma. To investigate why this decussation takes place, a series of embryological operations were performed in which one host eye was replaced by an eye from the opposite side of a donor in Xenopus laevis. The visual projections to the optic tecta were mapped electrophysiologically in these animals when adult to reveal to which side of the brain the nerve fibres had become connected. In the majority of cases the contralaterally grafted eyes had developed primary projections to both tecta, in others all the fibres had innervated the contralateral tectum and in 2 animals optic axons were detected only from the ipsilateral side. In 2 other animals optic nerve fibres from both the normal and operated eyes had innervated both tecta. Control experiments showed that section of the optic nerve and stalk without any misalignment of the eye and stalk did not disturb the normal decussation of the fibres. Neither did enucleation in the embryo affect the decussation of the fibres from the remaining eye. It is concluded that no "side specificity" has been shown to exist to determine the side of the brain into which retinotectal fibres develop; rather it seems that complete decussation depends on the developing optic nerve fibres being able to enter a normally aligned optic stalk as they leave the eye.

Animals↗
PubMed1995

Two dimensional mapping of the perfusion of the retina and optic nerve head.

AIM: To present a new non-invasive method of performing a high definition topography of perfused vessels of the retina and the optic nerve head with simultaneous evaluation of blood flow. METHOD: By a combination of a laser Doppler flowmeter with a scanning laser system the perfusion of the retina and the optic nerve head is visualised. The principles of measuring blood flow by laser Doppler flowmetry are based on the optical Doppler effect: laser light scattered by a moving particle is shifted in frequency by an amount delta f. Our data acquisition and evaluation system is a modified laser scanning tomograph. The technical data are retinal area of measurement 2.7 mm x 0.7 mm, 10 degrees field with 256 points x 64 lines, measurement accuracy 10 microns, wavelength 670 nm and 790 nm, light power 100 microW and 200 microW, data acquisition time 2.048 s. Every line is scanned 128 times by a line sampling rate of 4000 Hz. By performing a discrete fast Fourier transformation over 128 intensities of each retinal point the laser Doppler shift is calculated for each retinal point. With these data a two dimensional map with 256 x 64 points of the retinal perfusion is created. The brightness of the pixel is coded by the value of the Doppler shift. Offline capillary blood flow is estimated in arbitrary units according to the theory of laser Doppler flowmetry in every region of interest of the perfusion picture. We estimated the reliability and the validity of the method. Retinal blood flow was measured by scanning laser Doppler flowmetry (SLDF) while varying intraocular pressure by a suction cup of three healthy volunteers. Measurements of retinal blood flow performed in 47 eyes by the presented method (SLDF) were correlated with data gained by a commercially available laser Doppler flowmeter. Perfusion pictures of the superficial retinal layer and of deep prelaminar layers in the optic nerve head are presented. RESULTS: The reliability coefficients r1 of 'flow', 'volume', and 'velocity' were 0.84, 0.85, and 0.84 respectively. We found a significant linear relation between SLDF flow and the ocular perfusion pressure (r = 0.84, p < 0.001). Comparative measurements of the retinal blood flow by SLDF and a commercially available laser Doppler flowmeter showed a linear and significant relation (flow r = 0.6, p < 0.0001, volume r = 0.4, p < 0.01). Capillaries of the retinal superficial vasculature or deep ciliary sourced capillaries of the optic nerve head became visible with a high resolution by the confocal technique dependent on the focus. Offline, the blood flow variables of areas of 100 microns x 100 microns were calculated. CONCLUSION: SLDF enables the visualisation of perfused capillaries and vessels of the retina and the optic nerve head in high resolution by two dimensional mapping of perfusion variables which are encoded by the Doppler signal. This method achieves simultaneously qualitative and quantitative evaluation of capillary blood flow of distinct areas of the capillary meshwork.

Humans↗
PubMed1999

Changes in optic nerve head blood flow and retrobular hemodynamics following calcium-channel blocker treatment of normal-tension glaucoma.

BACKGROUND: Because calcium channel blockers reduce vascular resistance, they may have a clinical application in the treatment of normal-tension glaucoma (NTG). This study investigates changes in both the optic disc blood flow and the hemodynamics of retrobulbar vessels in NTG patients after the systemic administration of a calcium channel blocker. METHODS: Twelve eyes of 12 NTG patients (mean age 57.6 +/- 15.3 years) were examined before and after a 4-week treatment with 2 mg b.i.d. oral nilvadipine, an L-typc calcium channel blocker. By scanning laser-Doppler flowmetry (SLDF), we obtained the velocity, flow, and volume from within a 10 x 10 pixel window placed on the temporal rim region of the optic disc perfusion map. By ultrasound color Doppler imaging (CDI), we measured the peak systolic velocity (PSV) and the end diastolic velocity (EDV) of the ophthalmic artery (OA), central retinal artery (CRA), nasal posterior ciliary artery (NPCA), and temporal posterior ciliary artery (TPCA). We then calculated a resistance index (RI) for each vessel. RESULTS: After treatment, the flow and velocity of the optic disc blood flow significantly increased (P < 0.05). Nilvadipine also significantly reduced RIs of the CRA, NPCA, and TPCA (P < 0.05), and increased both the PSV of the NPCA and the EDVs of the CRA, NPCA, and TPCA. The percent change in velocity correlated significantly with the percent changes of the CRA RI and NPCA RI. CONCLUSIONS: Oral nilvadipine appears to reduce orbital vascular resistance, which consequently increases the optic disc blood flow.

Adult↗
PubMed1994

Functional mapping of horizontal connections in developing ferret visual cortex: experiments and modeling.

In cat striate cortex, patchy horizontal axonal projections link columns of similar orientation specificity. To assess the physiological correlates of such clustered projections, a new multisite stimulation technique was used to functionally map the pattern of horizontal synaptic inputs onto single layer 2/3 cells within tangential slices of developing ferret visual cortex. Twenty-four separate sets of horizontal fibers were stimulated within a 1200 microns strip of cortex, while evoked synaptic responses were recorded using whole-cell patch methods. For most cells, input maps demonstrated the presence of clustered horizontal connections in which multiple strong and weak synaptic responses were alternately evoked across the stimulated cortical region. Recordings from up to nine cells in a single slice revealed that patterns of synaptic input were closely correlated for cells in close proximity, and that this correlation decreased with distance, with no correlation at distances greater than 500 microns. To determine whether these physiological results were consistent with the known anatomical linkage of iso-orientation columns by clustered horizontal connections, mathematical analysis and computer simulations were performed upon orientation tuning maps obtained from optical imaging of activity-dependent intrinsic signals in mature ferret visual cortex. Optical imaging revealed an organization of iso-orientation domains consisting of broad regions of cortex across which orientation preference smoothly varied, together with "orientation centers" around which orientation preference was arranged in a pinwheel manner. The distribution of synaptic connections between different cortical sites was simulated by a model of functionally linked iso- orientation columns. Simulated synaptic input maps, generated by the same stimulation and recording arrangements used in our experimental protocol, accurately reproduced the observed patterns of clustered inputs onto experimentally recorded cells. These results indicate that even at the time of eye opening, prior to extensive visual experience, most cells receive patterns of synaptic inputs consistent with a clustered organization of horizontal connections that functionally link iso-orientation columns.

Animals↗
PubMed1999

The critical period for ocular dominance plasticity in the Ferret's visual cortex.

Microelectrode recordings and optical imaging of intrinsic signals were used to define the critical period for susceptibility to monocular deprivation (MD) in the primary visual cortex of the ferret. Ferrets were monocularly deprived for 2, 7 or >14 d, beginning between postnatal day 19 (P19) and P110. The responses of visual cortical neurons to stimulation of the two eyes were used to gauge the onset, peak, and decline of the critical period. MDs ending before P32 produced little or no loss of response to the deprived eye. MDs of 7 d or more beginning around P42 produced the greatest effects. A rapid decline in cortical susceptibility to MD was observed after the seventh week of life, such that MDs beginning between P50 and P65 were approximately half as effective as those beginning on P42; MDs beginning after P100 did not reduce the response to the deprived eye below that to the nondeprived eye. At all ages, 2 d deprivations were 55-85% as effective as 7 d of MD. Maps of intrinsic optical responses from the deprived eye were weaker and less well tuned for orientation than those from the nondeprived eye, with the weakest maps seen in the hemisphere ipsilateral to the deprived eye. Analysis of the effects of 7 d and longer deprivations revealed a second period of plasticity in cortical responses in which MD induced an effect like that of strabismus. After P70, MD caused a marked loss of binocular responses with little or no overall loss of response to the deprived eye. The critical period measured here is compared to other features of development in ferret and cat.

Aging↗
PubMed1993

Clinical implications of the fibre order in the optic pathway of primates.

Traditional neuro-ophthalmologic accounts of the optic pathway in primates stipulate that two half-retinal maps, one from each optic nerve, are combined within the chiasmatic region to yield a single, unified representation of the contralateral visual hemi-field in each optic tract. Yet visual disturbances produced by compromise to the visual pathways in the region of the describes recent neuroanatomical studies in monkeys that contradict those classical accounts but are consistent with the incongruous field defects and the functionally selective visual impairments documented in the clinical literature.

Animals↗
PubMedDate not supplied

Superimposed maps of the monocular visual fields in the caudolateral optic tectum in the frog, Rana pipiens.

The superficial layers of the frog optic tectum receive a projection from the contralateral eye that forms a point-to-point map of the visual field. The monocular part of the visual field of the contralateral eye is represented in the caudolateral region of the tectum while the binocular part of the visual field is represented in the rostromedial tectum. Within the representation of the binocular field (rostromedial tectum), the maps of visual space from each eye are aligned. The tectal representation of the binocular visual field of the ipsilateral eye is mediated through a crossed projection from the midbrain nucleus isthmi. This isthmotectal projection also terminates in the caudolateral region of the optic tectum, yet there has been no indication that it forms a functional connection. By extracellular recording in intermediate layer 7 of the caudolateral tectum, we have discovered electrical activity driven by visual stimulation in the monocular visual field of the ipsilateral eye. The units driven from the ipsilateral eye burst upon initial presentation of the stimulus. At individual layer 7 recording sites in the caudolateral tectum, the multiunit receptive field evoked from the ipsilateral eye is located at the mirror image spatial location to the multiunit receptive field driven by the contralateral eye. Thus, as revealed electrophysiologically, there are superimposed topographic maps of the monocular visual fields in the caudolateral tectum. The ipsilateral eye monocular visual field representation can be abolished by electrolytic ablation of contralateral nucleus isthmi.

Animals↗
PubMed1997

Short-term functional plasticity of cortical and thalamic sensory representations and its implication for information processing.

We studied phenomena, constraints, rules, and implications of cortical plastic reorganization produced by input coactivation patterns in primary somatosensory cortex of adult rats. Intracortical microstimulation (ICMS) and an associative pairing of tactile stimulation (PPTS) induced plastic changes within minutes to hours that were fully reversible. Reorganization of receptive fields and topographic maps was studied with electrophysiologic recordings, mapping techniques, and optical imaging of intrinsic signals. Utilizing the specific advantages of local application of ICMS, we investigated lamina-specific properties of cortical representational plasticity, revealing a prominent role of the input layer IV during plastic reorganization. To study subcortical plasticity, we compared ICMS and intrathalamic microstimulation (ITMS), revealing robust thalamic reorganizations that were, however, much smaller than cortical changes. Using PPTS, we found significant reorganizational processes at the cortical level, including receptive fields, overlap, and cortical representational maps. The protocol was similarly effective at the perceptual level by enhancing the spatial discrimination performance in humans, suggesting that these particular fast plastic processes have perceptual consequences. The implications were discussed with respect to parallel changes of information processing strategies. We addressed the question of the possible role of RF size and size of cortical area, inhibitory mechanisms, and Hebbian and non-Hebbian learning rules. The short time scale of the effects and the aspect of reversibility support the hypothesis of fast modulations of synaptic efficiency without necessarily involving anatomic changes. Such systems of predominantly dynamically maintained cortical and adaptive processing networks may represent the neural basis for life-long adaptational sensory and perceptual capacities and for compensational reorganizations following injuries.

Animals↗
PubMed1994

Dynamics of propagating waves in the olfactory network of a terrestrial mollusk: an electrical and optical study.

1. The procerebral (PC) lobe of the terrestrial mollusk Limax maximus contains a highly interconnected network of local olfactory interneurons that receives ipsilateral axonal projections from superior and inferior noses. This network exhibits an approximately 0.7-Hz intrinsic oscillation in its local field potential (LFP). 2. Intracellular recordings show that the lobe contains at least two classes of neurons with activity phase locked to the oscillation. Neurons in one class produce periodic bursts of spikes, followed by a period of hyperpolarization and subsequently a depolarizing afterpotential. There is a small but significant chance for a second burst to occur during the depolarizing afterpotential; this leads to a double event in the LFP. Bursting neurons constitute approximately 10% of the neurons in the lobe. 3. Neurons in the other class fire infrequently and do not produce periodic bursts of action potentials. However, they receive strong, periodic inhibitory input during every event in the LFP. These nonbursting cells constitute the major fraction of neurons in the lobe. There is a clear correlation between the periodic burst of action potentials in the bursting neurons and the hyperpolarization seen in nonbursting neurons. 4. Optical techniques are used to image the spatially averaged transmembrane potentials in preparations stained with voltage-sensitive dyes. The results of simultaneous optical and electrical measurements show that the major part of the optical signal can be interpreted as a superposition of the intracellular signals arising from the bursting and nonbursting neurons. 5. Successive images of the entire PC lobe show waves of electrical activity that span the width of the lobe and travel its full length along a longitudinal axis. The direction of propagation in the unperturbed lobe is always from the distal to the proximal end. The wavelength varies between preparations but is on the order of the length of the preparation. 6. One-dimensional images along the longitudinal axis of the lobe are used to construct a space-time map of the optical activity, from which we calculate the absolute contribution of bursting and nonbursting neurons to the optical signal. The contribution of the intracellular signals from the two cell types appears to vary systematically across the lobe; bursting cells dominate at middle and proximal locations, and nonbursting cells dominate at distal locations. 7. The direction and form of the waves can be perturbed either by microsurgical manipulation of the preparation or by chemical modulation of its synaptic and neuronal properties.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2006

Subsurface Raman spectroscopy and mapping using a globally illuminated non-confocal fiber-optic array probe in the presence of Raman photon migration.

We report the use of a fiber-optic probe with global illumination and an array of 50 collection fibers (PhAT probe, Kaiser Optical Systems, Inc.) to obtain Raman spectra and 50 spatial element maps of polymers through overlayers of other polymers that are highly scattering. Band target entropy minimization (BTEM) is used to recover the spectra of the subsurface components and generate maps of their distributions. This approach to subsurface mapping is tested with model systems consisting of two or three layers of polyethylene, polytetrafluoroethylene (Teflon), and polyoxymethylene (Delrin) arranged in different geometries. Raman spectra and maps were obtained through overlayer thicknesses of up to 13 mm. Subsurface spatial resolution is achieved because each fiber views an asymmetric distribution of Raman scattered light from surface and subsurface components that depends on the position of the fiber relative to the depth and position of a component and the extent of photon diffusion through the system.

Equipment Design↗
PubMed1986

Map of retinal position onto the cross section of the optic pathway of goldfish.

The position of a retinal cell is defined by the two polar coordinates: r, the distance from the optic disc, and theta, the angular (or clock-face) position. Axons of similar theta value were labeled by the punctate application of horseradish peroxidase (HRP) to optic axons in the retina, and axons of similar r-value were labeled by the application of this same marker to a tectal fascicle. Labeled axons were traced in serial transverse sections of the optic pathway from the retina to the tectum to learn the map of the retinal surface onto the cross section of the pathway. Retinas were flat-mounted and treated for HRP to show the retinal origins of the labeled axons. Axons of similar r were clustered together, and the fraction of the pathway's cross-sectional area occupied by the cluster was about the same as the fraction of the retinal area occupied by the group of labeled somata. Axons of similar theta were also clustered, but the fraction of the cross-sectional area they occupied was larger than the fraction of retinal area occupied by their somata. The geometry of the clusters of labeled axons depended on the proximodistal location in the pathway. Near the retina both were strip-shaped, but the location and orientation of the strip varied. Both an r-strip and a theta-strip were labeled in some pathways by dual applications of HRP; the two strips were mutually orthogonal at all levels. Each of r and theta mapped onto a separate axis. The axons from most peripheral retina (largest r) were everywhere adjacent to the pia, and axons of progressively more central retina (smaller r) were progressively more separated from the pia (except in the nerve, where the secondary fasciculation complicates the geometry by wrapping old axons in new pia). The map of the circular variable, theta, onto a line, required a discontinuity, the location of which differed, depending on the proximodistal level. From the retina to the chiasm, the discontinuity was at the ventral retinal radius (i.e., the right retinal clock-face positions were ordered 6-9-12-3-6 o'clock across the line); just central to the chiasm, the fibers reordered to put the discontinuity at the nasal radius (clock-face positions ordered 3-6-9-12-3); at the brachial bifurcation, the 3-6-9 half turned dorsally, the 9-12-3 half, ventrally.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2006

Mapping arrhythmias in the failing heart: from Langendorff to patient.

Sudden cardiac death due to ventricular arrhythmias is a major cause of mortality in patients with heart failure (HF). As HF develops, a host of changes occur at multiple levels, spanning the spectrum from subcellular/molecular to organ-system levels. These changes, collectively referred to as "cardiac remodeling," predispose to electrical disturbances via multiple mechanisms. In humans, most arrhythmias are reentrant by nature, involving circulatory wavefront(s) that excite the heart in rapid, irregular succession. Hence, by definition, reentrant excitation occurs at the multicellular intact tissue level, and therefore, a complete understanding of its dynamics and underlying mechanisms requires investigation of electrophysiological properties (such as action potentials and calcium transients) in intact tissue preparations where cells are electrically coupled to one another. While molecular and cellular studies are critical for identifying changes in individual myocytes, only recently have we begun to understand how these complex changes can create an environment ripe for arrhythmias. In particular, the integrative technique of optical action potential mapping was used in recent years to address key questions regarding changes in network electrical properties of the failing myocardium. In the present manuscript, we review recent findings from mapping studies in the experimental laboratory as they relate to the characterization of the arrhythmic substrate of the failing heart, followed by a discussion of clinical mapping approaches used to identify key characteristics of atrial and ventricular arrhythmias in patients with HF.

Animals↗
PubMed2006

Localized measurement of the optical thickness of a transparent window: application to the study of the photosensitivity of organic polymers.

The development of an optical setup that permits us to carry out high-resolution mappings of the absolute optical thickness of plane-parallel transparent windows is described. This measurement is based on the recording and processing of the spectral transmission of the wafer between 1,520 and 1,570 nm and has a relative precision better than 10(-6). Hence it is used for the characterization of the photosensitivity of two organic photopolymers (cationic ring opening polymer and poly(methylmethacrylate)). The refractive index change dynamics for both materials and the spontaneous evolution of the optical thickness are demonstrated.

Journal Article↗
PubMed2006

Thermal radiation scanning tunnelling microscopy.

In standard near-field scanning optical microscopy (NSOM), a subwavelength probe acts as an optical 'stethoscope' to map the near field produced at the sample surface by external illumination. This technique has been applied using visible, infrared, terahertz and gigahertz radiation to illuminate the sample, providing a resolution well beyond the diffraction limit. NSOM is well suited to study surface waves such as surface plasmons or surface-phonon polaritons. Using an aperture NSOM with visible laser illumination, a near-field interference pattern around a corral structure has been observed, whose features were similar to the scanning tunnelling microscope image of the electronic waves in a quantum corral. Here we describe an infrared NSOM that operates without any external illumination: it is a near-field analogue of a night-vision camera, making use of the thermal infrared evanescent fields emitted by the surface, and behaves as an optical scanning tunnelling microscope. We therefore term this instrument a 'thermal radiation scanning tunnelling microscope' (TRSTM). We show the first TRSTM images of thermally excited surface plasmons, and demonstrate spatial coherence effects in near-field thermal emission.

Journal Article↗
PubMed2004

Near-field microscopy by elastic light scattering from a tip.

We describe ultraresolution microscopy far beyond the classical Abbe diffraction limit of one half wavelength (lambda/2), and also beyond the practical limit (ca. lambda/10) of aperture-based scanning near-field optical microscopy (SNOM). The 'apertureless' SNOM discussed here uses light scattering from a sharp tip (hence scattering-type or s-SNOM) and has no lambda-related resolution limit. Rather, its resolution is approximately equal to the radius a of the probing tip (for commercial tips, a < 20 nm) so that 10 nm is obtained in the visible (lambda/60). A resolution of lambda/500 has been obtained in the mid-infrared at lambda = 10 microm. The advantage of infrared, terahertz and even microwave illumination is that specific excitations can be exploited to yield specific contrast, e.g. the molecular vibration offering a spectroscopic fingerprint to identify chemical composition. S-SNOM can routinely acquire simultaneous amplitude and phase images to obtain information on refractive and absorptive properties. Plasmon- or phonon-resonant materials can be highlighted by their particularly high near-field signal level. Furthermore, s-SNOM can map the characteristic optical eigenfields of small, optically resonant particles. Lastly, we describe theoretical modelling that explains and predicts s-SNOM contrast on the basis of the local dielectric function.

Equipment Design↗