Pencil Of Light Research Articles

Identify the limits of geometric optics ray tracing by numerically solving the vector Kirchhoff integral.

The properties of a pencil of light as defined approximately in the geometric optics ray tracing method are investigated. The vector Kirchhoff integral is utilized to accurately compute the electromagnetic near field in and around the pencil of light with various beam base sizes, shapes, propagation directions and medium refractive indices. If a pencil of light has geometric mean cross section size of the order p times the wavelength, it can propagate independently to a distance p2 times the wavelength, where most of the beam energy diffuses out of the beam region. This is consistent with a statement that van de Hulst made in a classical text on light scattering. The electromagnetic near fields in the pencil of light are not uniform, have complicated patterns within short distances from the beam base, and the fields tend to converge to Fraunhofer diffraction fields far away from the base.

Halo and subsurface scattering in the transparent coating on top of a diffusing material.

Strongly scattering supports coated with thick transparent medium display a bright halo with a characteristic ring shape when illuminated in one point by a thin pencil of light. The halo, whose size is related to the coating thickness, is due to the Fresnel internal reflections of the light scattered by the diffusing support at the coating-air interface. The angular distribution of the reflected light strongly varies over the halo according to the distance from the point initially illuminated, a fact that cannot be observed when a large area of the surface is illuminated as in usual reflectance and bidirectional reflectance distribution function measurements. By considering a Lambertian background and a transparent layer on top of it, both of them being possibly absorbing, we develop a bidirectional subsurface scattering reflectance distribution function model, based on analytical equations and matrix numerical computation, which enables a detailed description of the spatial and angular distribution of the scattered light including the multiple reflections between the background and the coating-air interface. Some applications in which this subsurface scattering phenomenon can be an issue are addressed, such as the reflectance measurement, which can be undervalued when the geometry is not adapted to the coating thickness, or the impact of the phenomenon on heterogeneously colored surfaces such as coated or laminated halftone prints.

Readers offer their own magic moments with John Bell

Here are some memories of my own “magic moments” with John Bell. I first met John in 1962, when I spent a sabbatical year at CERN from MIT. We had fruitful discussions on longitudinal sum rules arising from moments of the density–density correlation function in N-body systems, which were later incorporated into my book on statistical mechanics.11. K. Huang, Statistical Mechanics, 2nd ed., Wiley (1987), sec. 13.7, app. A.4. 978-0-471-81518-1The second time I saw John was in 1964, I think, at the physics summer school at the University of Washington in Seattle. Rudolf Peierls was also present, and the three of us discussed a question I brought up: why a point source of light on a lake shore produces a point image in calm water but a long pencil of light when there are ripples. We did not reach a conclusive answer.On a weekend trip, I drove John and his wife, Mary, to visit Olympic National Park in Washington State. Coming back from a rest stop, John reported that a group of children had pointed at his beard and said, “Look! Hippie! Hippie!” John said children learn things fast because “childhood is boring.” We talked about various subjects on that trip. He was a vegetarian because of Mary, but one time on the road he had no choice but to stop at McDonald’s for a hamburger. “It was delicious,” he said.At the Pacific Ocean shore in the park, John decided he had to take a dip. We both waded in but could only stay a few minutes because the water was very cold. When we walked back to the car, there was another car beside mine, and an elderly couple had gotten out, apparently waiting to speak to us. The wife said that they saw the MIT parking sticker on my car; did I happen to know their son, a senior in physics at MIT? His name is Ising. I said, as a matter of fact, I did know a student named Ising. And she said, “This is my husband, Dr. Ising. He teaches physics at the Central College in Peoria, Illinois. Have you heard of the Ising model?” I said, “Of course! I wrote a textbook with a chapter devoted to it.” Dr. Ising was diffident and embarrassed.REFERENCESSection:ChooseTop of pageREFERENCES <<1. K. Huang, Statistical Mechanics, 2nd ed., Wiley (1987), sec. 13.7, app. A.4. 978-0-471-81518-1, Google Scholar© 2015 American Institute of Physics.

The effect of fine and grapho-motor skill demands on preschoolers’ decoding skill

Previous correlational research has found indications that fine motor skills (FMS) link to early reading development, but the work has not demonstrated causality. We manipulated 51 preschoolers’ FMS while children learned to decode letters and nonsense words in a within-participants, randomized, and counterbalanced single-factor design with pre- and posttesting. In two conditions, children wrote with a pencil that had a conical shape fitted to the end filled with either steel (impaired writing condition) or polystyrene (normal writing condition). In a third control condition, children simply pointed at the letters with the light pencil as they learned to read the words (pointing condition). Results indicate that children learned the most decoding skills in the normal writing condition, followed by the pointing and impaired writing conditions. In addition, working memory, phonemic awareness, and grapho-motor skills were generally predictors of decoding skill development. The findings provide experimental evidence that having lower FMS is disadvantageous for reading development.

On the gravity of light

A solution of the old problem raised by Tolman, Ehrenfest, Podolsky and Wheeler, concerning the lack of attraction of two light pencils ‘moving parallel’, is proposed, considering that the light can be a source of nonlinear gravitational waves corresponding (from a quantum point of view) to spin-1 massless particles.

Elastic Fully Three‐dimensional Microstructure Scaffolds for Cell Force Measurements

2010 WILEY-VCH Verlag Gm Mechanical interactions between cells and their environment play an important role in regulating many cellular functions, such as migration, differentiation, and proliferation. They are also involved in complex processes like tissue formation during development of multicellular organisms. During the last two decades, several methods have been developed to visualize and measure traction forces produced by single cells. Initial experiments were performed by growing fibroblasts on a thin silicon rubber substrate that was deformed by forces exerted by migrating cells. Subsequently, elastic polyacrylamide substrates embedded with fluorescent latex beads were used to get an insight into the force vectors exerted by the cells. These methods were further improved by producing regular arrays of traceable markers in the elastic substrates allowing a quantification of traction forces exerted by adhering cells. A different approach has used arrays of elastic posts positioned on a flat 2D substrate, coated with extracellular-matrix (ECM)molecules. Because each post effectively acts like a harmonic spring, local traction forces at multiple cell adhesion sites could then be measured by simply monitoring post deflections. A modification of this assay was recently applied to measure contraction forces of single cardiomyocytes. Although these different approaches have provided valuable insight into our understanding of cellular forces, they have the disadvantage that the cells are forced into a 2D growth pattern, which significantly differs from the in vivo situation. Therefore, the development of in vitro model systems that capture more of the complexity present in 3D tissue scaffolds are highly desirable. Technologies for fabricating macroscopic tissue architectures in the millimeter and micrometer range have become available only during recent years. In contrast, methods to reliably produce flexible 3D cellular environments in the micrometer to nanometer range are still missing. Ideally, these scaffolds should have a controllable distribution of cell-substrate contact sites and an adjustable stiffness. In this Communication, we show that such biocompatible scaffolds can be fabricated by means of direct laser writing (DLW) and subsequent surface functionalization. We furthermore demonstrate that these scaffolds can be rhythmically deformed by single beating cardiomyocytes. In addition, we quantitatively evaluate the involved contraction forces by calibrating these structures using atomic force microscopy (AFM). In particular, with the method presented here, beamlike structures with defined geometries and physiologically relevant stiffness values can be produced; thus, these scaffolds structurally and mechanically mimic large macromolecules surrounding cells in 3D tissues, such as collagen fibrils. In essence, DLW (see the Experimental section) can be thought of as a pencil of light in three dimensions. Any connected structure envisioned on a computer can easily be implemented by scanning a photoresist relative to the focus of a femtosecond-laser beam (Fig. 1a). After development of a negative resist, sufficiently exposed regions correspond to the remaining polymer (Fig. 1b). Lithography of 3D polymeric templates by DLW with lateral feature sizes down to the 100 nm range has become routine in the field of nanophotonics. Along these lines, fully 3D (Fig. 1c) scaffolds can be fabricated. Sample footprints of mm up to cm dimensions can be realized by combining 300mm 300mm areas that are accessible within the piezo scanning range. The height of the structures is limited only by the working distance of the microscope lens (80mm in our case). Typical writing times for the structures shown in this Communication are less than 10min. Here, we employ the commercially available resist system Ormocomp (obtained from Micro Resist Technology GmbH). Ormocomp is a member of Ormocer, a class of inorganic (Si O Si)–organic hybrid polymer systems, previously developed at the Fraunhofer Institute for Silica Research (Wurzburg, Germany). Its detailed chemical composition is proprietary. With Ormocomp as a photoresist, complex fully 3D structures (Fig. 1a–c) can be easily manufactured and, after functionalization with fibronectin, directly used for cell culture (Fig. 1d). To demonstrate that single cells can lead to noticeable deformation of the 3D Ormocomp scaffolds, primary cardiomyocytes are isolated from chicken embryos (see the

CYCLADIC IDYLL: AN APOLOGIA

9 2 Y C Y C L A D I C I D Y L L A N A P O L O G I A S T E P H E N Y E N S E R ‘‘I don’t know why you don’t just go over to Catalina.’’ – Bill Edinger 1 I come here for the views. I come because there is no news. Because things have been arranged. Because I have no other plans. Because there are no plans for me. Because I do not have to choose. I come here for the arid, aromatic, aromantic emptiness – where one might ‘‘get a grip’’ and ‘‘sort things out.’’ Add them up. Make some sum. Compose oneself – like a concerto for flute and strings. I come to be alone. Because I am alone. Out of season. Like the few midges left. Adrift on a stony island no known poet hails from. Enisled. Outlandish as that term. (Annihiled is di√erent but only by a smidge.) To remind myself how simple things can be. Simple as the music of the marble figures of the harpist – and the unique double-reed player. Not to mention concepts. To remind myself how when it comes to things like concepts, Heraclitus and Plato had all we would ever need. (Pythagoras I set aside for now.) 9 3 R I come here to learn to speak clearly. To make carefully with the right mouthparts the sounds for thing and nothing, for bread and wine, for come and go, here and now and then and there. For good evening and farewell. Because my own language has become extravagant and tra-la, tra-la. Tralatitious, one might say. And – the olives everywhere remind me – indecently indehiscent. Because I want fewer such words to weigh. To be less weighword, so to say. Therefore less wayward and less spendthrift. Less spindrift, in a word. Not to mention grave, preponderant, and dark. (I come here to be struck by lightening !) Because here in the right place a thésis can be a good flat stone to sit on and not a lizardlike thing to nail down then argue with. Because here amid abandoned villages’ abundant dilapidation there is no reason for reason, no urge to originality. Because as I wait to be transported by the bus I read on small trucks that ply the main road the descriptor Metaphorá. I come here to sit at length and read some Whitman, who adored words plain as stones, regardless of those exultant exaltations of ‘‘eidolons.’’ To browse idly, to idle on in a brief, worn lexicon, to let it lead me on. Because I need new old sayings. Because the good ones die too soon. Because bean by bean fills the bag. Because I will save time, because it will not save me, here where it twists on itself like the walkways to waylay laid-up freebooters like me and my dead friend. 9 4 Y E N S E R Y 2 I come back to stop in on the way to see this time by appointment Edward Lear’s watercolors in the Gennadius, Because he did them as sketches for oils he could paint then sell back home, so they were valueless themselves, so they were kept unmatted and loose in cartons pulled o√ shelves thirty years ago for improvident visitors like me and my friend who was my guide to shuΔe through and take quick notes like these on his. Because even this delicate, vehicular medium meant fixity, his nemesis, so in hopes that glazed and scumbled oils could get the shifty shades right, he jotted in light pencil across the images descriptions, shot through with nonce terms and puns fleeting as pains taken, rubbed and faded, sometimes indecipherable, wishful notes written on washes disappearing before our eyes, which follow them, into sea, cli√, olive stand, distant temple, dovecote, asphodel. ‘‘catch gold light grass’’ ‘‘all turquoisy & Byzantine bluesy’’ ‘‘O poppies!’’ ‘‘very olivish’’ 3 I come here not to contemn my city’s columbaria of condominiums and book emporia with their stacks of fresh books on chocolate chockablock with guides to the Galápagos and Godot and...

‘The calotype’

There are some two or three slight advantages which real merit has, that fictitious merit has not; among the rest, an especial advantage, which, we think, should recommend it to at least the quieter members of society — the advantage of being unobtrusive and modest. It presses itself much less on public notice than its vagabond antagonist, and makes much less noise; it walks, for a time at least, as if slippered in felt, and leaves the lieges quite at freedom to take notice of it or no, as they may feel inclined. It is content, in its infancy, to thrive in silence. It does not squall in the nursery, to the disturbance of the whole house, like ‘the major roaring for his porridge’. What, for instance, could be quieter or more modest, in its first stages, than the invention of James Watt? What more obtrusive and noisy, on the contrary, than the invention of Mr Henson? And we have illustrations of the same truth in our Scottish metropolis at the present moment that seem in no degree less striking. Phrenomesmerism and the calotype have been introduced to the Edinburgh public at much the same time; but how differently have they fared hitherto! A real invention, which bids fair to produce some of the greatest revolutions in the fine arts of which they have ever been the subject, has as yet attracted comparatively little notice; an invention which serves but to demonstrate that the present age, with all its boasted enlightenment, may yet not be very unfitted for the reception of superstitions the most irrational and gross, is largely occupying the attention of the community and filling column after column in our public prints. We shall venture to take up the quieter invention of the two as the genuine one — as the invention that will occupy the most space a century hence — and direct the attention of our readers to some of the more striking phenomena which it illustrates and some of the purposes which it may be yet made to subserve. There are few lovers of art who have looked on the figures or landscapes of a camera obscura without forming the wish that, among the hidden secrets of matter, some means might be discovered for fixing and rendering them permanent. If nature could be made her own limner, if by some magic art the reflection could be fixed upon the mirror, could the picture be other than true? But the wish must have seemed an idle one — a wish of nearly the same cast as those which all remember to have formed at one happy period of life, in connection with the famous cap and purse of the fairy tale. Could aught seem less probable than that the forms of the external world should be made to convert the pencils of light which they emit into real bona fide pencils, and commence taking their own likenesses? Improbable as the thing may have seemed, however, there were powers in nature of potency enough to effect it, and the newly discovered art of the photographer is simply the art of employing these. The figures and landscapes of the camera obscura can now be fixed and rendered permanent — not yet in all their various shades of colour, but in a style scarcely less striking, and to which the limner, as if by anticipation, has already had recourse. The connoisseur unacquainted with the results of the recent discovery would decide, if shown a set of photographic impressions, that he had before him the carefully finished drawings in sepia of some great master. The stronger lights, as in sketches done in this colour, present merely the white ground of the paper; a tinge of soft warm brown indicates the lights of lower tone; a deeper and still deeper tinge succeeds, shading by scarce perceptible degrees through all the various gradations, until the darker shades concentrate into an opaque and dingy umber that almost rivals black in its intensity. We have at the present moment before us — and very wonderful things they certainly are — drawings on which a human pencil was never employed. They are strangely suggestive of the capabilities of the art.

Infrared thermographic image processing for the operation and control of heterogeneous combustion chambers

The measurement of temperature in a combustion chamber, using conventional devices such as thermocouples, can be misleading. An infrared thermographic camera can achieve a non-intrusive measure. Having acquired a still image of, for example, a klin, it can be used to produce a map of the effective temperature of the waste bed, walls, and combustion gases. This paper describes a technique for processing an infrared image to identify what really happens within such a combustion chamber. The use of a thermographic camera, to produce a temperature map of a combustion chamber, can be helpful, particularly for control purposes. This paper addresses the criteria adopted in the selection of the thermographic system, in terms of both wavelength sensitivity and geometric location within the chamber. Moreover, a detailed description of the zonal method is reported, together with the identification procedure adopted to infer the temperature map from an infrared image. As a matter of fact, the presence of soot and fly-ash within the combustion chamber does complicate the radiative model, because a gray gas analogy must be accounted for. Soot and fly-ash give rise to a foggy and diffusive effect on the image with a consequent apparent homogeneous temperature profile. To simulate the effective radiative energy flux entering the camera lens and impinging on the CCD photoelectric cell, a raytracing technique has been developed. Each discrete area and volume, within the combustion chamber, emits a pencil of radiation, which after passing through the hot gases, reaches the CCD device. Such a light pencil is generated by the energy emitted and reflected from the discrete surfaces, plus all the energies emitted by the volumes of gas distributed along the path, minus any attenuation. The total energy balance equations, coming from the zonal method, must be coupled with the temperature-energy maps acquired by the infrared camera to identify the unknown effective temperatures. Once the temperatures of the walls and bed are known, it is possible to use them to improve the control strategy by means of a set of new measures and combustion efficiency indexes, which are usually unavailable when conventional thermocouples are adopted. Finally, a validation of the proposed procedure is presented with an online application to an incinerator for industrial solid waste. The combustion dynamics within the primary kiln is analyzed and quantified, in terms of both absolute temperatures and characteristic times.

Using literature to help troubled teenagers cope with end-of-life issues

Introduction Helping Teens Cope through Sharing Their Stories about Death Discovering Life in Death: Confronting AIDS-related End-of-Life Giving Words to the Grief: Using Two Moons in August, Saying It Out Loud, and Tiger Eyes to Explore the Death of a Parent Making Sense of Sibling Loss: Using A Summer to Die as a Guide through the Grief Journey Legacies of Our Lives: Exploring the Loss of a Grandparent with A Ring of Endless Light Pencils, Books and Guns: Violence Goes to School The Year Without Michael: Unresolved End-of-Life Issues Remembering the Good Times: Making a Life Memorable After Suicide Index

Global Doctrine and Local Knowledge: Law in South East Asia

The relationship between the global and the local is one of critical importance to all regions of the world. In the resolution of the tension between the irresistible surge of globalisation and the undeniable facts of society as it actually exists in the various localities which together comprise the very world which is presumably the object or the subject-matter of globalisation, law lies at the forefront. It is, one might say, the very intellectual battlefield which we have selected for the resolution of the major problem facing human society at the turn of the century. The purpose of this article is therefore to investigate, in a somewhat narrative fashion the relationship between the global and the local in the context of law in South East Asia. The topic is clearly too large to be dealt with in a short space with the rigour and articulation it really deserves, but it is hoped that the approach adopted will provide some kind of a frame of reference for regarding, studying, and hopefully improving, the law in the South East Asian region; and will perhaps focus a pencil of light on the problems of the global and the local in this particular regional context.

On image quality of microlens arrays in diurnal superposition eyes

High-resolution compound eyes of the superposition type have been found in some diurnal insects, suggesting high-quality optics. Here we study whether a superposition eye could potentially achieve a higher resolution than that of a single, diffraction-limited facet, like in modern optical instruments made of a number of facets. We have developed a schematic diffractional model of the particularly acute superposition eye of the diurnal lepidopteran agaristid moth Phalaenoides Tristifica, and estimated the amount of aberrations required to fit the experimental data. Our results show that if the ommatidia were perfect (aberration-free) and perfectly aligned towards a common centre O, the resolution of the superposition image would be about 10 times higher than that provided by a single facet, and this in spite of the large phase lags between the pencils of light stemming from neighbouring ommatidia, due to the spherical geometry of the eye. In the insect species taken as a model system here, however, retinal sampling is too coarse to take full advantage of the high spatial frequency content of the superposition image. We show that the experimental data can be fitted if aberrations such as misalignment are introduced. A corollary of these results is that a superposition compound eye which was better constructed and avoided misalignment would provide its host with a better resolution than its `apposition eye counterpart'. This might explain why some diurnal compound eyes such as that of the fast-flying lepidopteran Macroglossum can afford sampling the focal image with a number of rhabdom exceeding the number of ommatidia (Warrant et al 1998 J. Exp. Biol. at press).

Nonlinear optical beam propagation and solitons in photorefractive media

The last few years have witnessed a great renewal of interest in the photorefractive effect thanks to the realization of the possibility of propagating stable 2D spatial solitons at very low optical powers in PR crystals. This result, besides possessing a great scientific relevance in itself, associated with the first experimental demonstration of a non-diffracting two-dimensional pencil of light, has also an interesting applicative potential thanks to the guidance properties of the waveguide associated with the soliton, which survives in the dark also after the soliton has been turned off. In this paper, we have tried to present a self-contained approach to the theory of self-trapped nonlinear propagation, which is far from being definitive, together with the most important experimental demonstrations obtained in the last few years. The novelty of the field, and the fact that it is still undergoing a rapid growth, has made our task not an easy one and we apologize to the readers for the many inevitable omissions both in the subjects we have chosen to emphasize and in the references.

Aberrations and Relative Efficiency of Light Pencils in the Living Human Eye

Aberrations and Relative Efficiency of Light Pencils in the Living Human Eye

Aberrations and relative efficiency of light pencils in the living human eye.

We propose a new method for ray tracing in the living human eye. It consists of delivering a narrow light pencil from an unexpanded laser beam and recording the integrated energy and position of the aerial image formed by the outgoing beam (after reflection off the retina and passage through the fully open pupil of the eye and camera lens). The lateral displacement of the aerial image is proportional to the geometrical aberration (displacement) of the incoming ray at the retina. In addition, its integrated energy is proportional to retinal reflectance that is highly directional [related to the Stiles-Crawford (SC) effect and to the effective pupil transmittance]. This method permits us, by delivering rays through different equispaced positions at the pupil plane, to sample the complex pupil function: its magnitude is a measure of the effective pupil transmission and its phase is the wave aberration. Experimental results, aberrations, and reflectometric directionality for four subjects are consistent with previous findings.

Cupid's Pencil of Light: Julia Margaret Cameron and the Maternalization of Photography

When one thinks of Victorian images of come-hither children, it is Lewis Carroll that one probably thinks of first, but in fact it is Julia Margaret Cameron, the good mother and grandmother, who has left us with the more obsessive, the more insistent, and I think the more perverse record of a fascination with the allure of childish bodies. (Just one example would be Cameron's Infant Undine of 1864, with that pseudononchalant, crossed-foot pose, that slightly sullen, almost sultry look, that sliding slip, and its revelation of plumped baby flesh, recalled in contemporary images, such as Sally Mann's snapshotty yet Hollywoodish photograph of her daughter, Virginia at 3, which verge on child pornography, so people felt at the time of their exhibition.)' In fact, the image of the child was central to Cameron's practice right from the beginning, when she took up her camera in 1864 at the matriarchal age of forty-nine and recorded a village girl, Annie Philpot, as her first success in photography. Right from the start, the eroticized child was a mainstay--indeed, it is to 1864 that a good share of such pictures are dated (it is the year of The Infant Undine, The Double Star, and The Infant Bridal, for instance).

On the use of light sheet methods in the presence of refraction by flames

When a light sheet traverses a flame, refraction caused by optical density variations alters theillumination intensity downbeam. This can be a serious limitation for optical methods that presuppose a uniform intensity initially (or a distribution otherwise established by prior calibration) for the purposes of recording, for example, Mie or Rayleigh scattering, or planar laser-induced fluorescence. The theory of the light deflection is analyzed in terms of premixed flame parameters, and the consequent intensity redistribution is predicted as a function of distance downbeam. This indicates the magnitude of the problem and corresponds to observations on the experimental records that first drew attention to the phenomenon. The effects of temperature and pressure are predicted. The use of the theory to correct the results is assessed and, since that may prove a somewhat difficult process, various methods of correcting or avoiding the problem are put forward. They include optimizing the beam insertion, defining regions over which averaging conserves incident light energy, as well as a simple experimental technique based on breaking the sheet into individual thin beams, for example by introducing interference fringes in its plane. Their spacing may be varied so as to avoid overlap, and the recording system then operates on the total output from each pencil of light.

Methyl radical measurement by cavity ring-down spectroscopy

Cavity ring-down spectroscopy has been used to measure the absorbance of methyl radicals near 216 nm. The methyl radicals are generated by a hot tungsten filament heated to 2300 K in a mixture of 0.5% CH 4 in H 2 slowly flowing through the reactor at 20 Torr total pressure. CH 3 absorbances are detected with a noise-equivalent sensitivity of two parts in 10 5 using a narrow pencil of UV light 0.5 mm in diameter, which allows measurement of spatial profiles of CH 3 for column densities of 3×10 12 radicals/cm 2 (3×10 12 radicals/cm 3×1 cm absorption pathlength).

A pencil of light in the Bonnor-Melvin universe

On the basis of the approach to generation of Einstein-Maxwell fields proposed by Jan Horský and Nikolai Mitskievich, a magnetization of the pencil-of-light space-time is performed yielding a superposition of the fields of a spinning pencil of light and of the Bonnor-Melvin universe. An interplay of Petrov's types in this superposition is revealed. A generalization of Wald's theorem on test electromagnetic fields on a vacuum space-time background is achieved thus explaining applicability of our approach to space-times of the Levi-Civita type.

Optical fiber alignment using cleaved-edge diffracted light

We describe a simple technique for aligning optical fibers prior to fusion splicing. The technique relies on the fact that well-cleaved fiber ends have extremely sharp edges. By making the narrow pencil of light emerging from one fiber scan laterally over the entrance face of a second fiber, and by monitoring the light diffracted past its sharp edges, we can locate precisely the geometric center of the output fiber. With this technique, we have aligned fiber cores with a mean lateral offset of 0.81 μm, the major part of this offset caused by the eccentricity of the core relative to the cladding's circular perimeter.