Three-dimensional diffraction of a thin metallic cylinder illuminated in conical incidence: application to diameter estimation

Sanchez‐Brea, Luis Miguel; Salgado-Remacha, Francisco Javier

doi:10.1364/ao.47.004804

Cited by 6 publications

(8 citation statements)

References 10 publications

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“…Firstly, it is known that in the diffraction of a beam on a transparent dielectric cylinder, a series of arcs centered around the cylinder appears in the forward direction due to reflection from the cylinder's surface as well as refraction and transmission [45][46][47]. In the latter case, the cylinder works as a one-dimensional lens.…”

Section: Discussionmentioning

confidence: 99%

White-light generation control with crossing beams of femtosecond laser pulses

et al. 2016

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We investigated the variations in generated white-light when crossing two femtosecond laser beams in a Kerr medium. By changing the relative delay of two interacting intense femtosecond laser pulses, we show that white-light generation can be enhanced or suppressed. With a decrease of the relative delay an enhancement of the white-light output was observed, which at even smaller delays was reverted to a suppression of white-light generation. Under choosen conditions, the level of suppression resulted in a white-light output lower than the initial level corresponding to large delays, when the pulses do not overlap in time. The enhancement of the white-light generation takes place in the pulse that is lagging. We found that the effect of the interaction of the beams depends on their relative orientation of polarization and increases when the polarizations are changed from perpendicular to parallel. The observed effects are explained by noting that at intermediate delays, the perturbations introduced in the path of the lagging beam lead to a shortening of the length of filament formation and enhancement of the white-light generation, whereas at small delays the stronger interaction and mutual rescattering reduces the intensity in the central part of the beams, suppressing filamentation and white-light generation.

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Section: Discussionmentioning

confidence: 99%

White-light generation control with crossing beams of femtosecond laser pulses

et al. 2016

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“…Typically, Equation 1 assumes that Babinet's principle applies in the far field, i.e. the hair, wire or other cylindrical body can be equivalently substituted by an aperture within a screen whose dimension and position matches that of a two dimensional projection of the body into the plane of observation [21]. However, students might query how the light can diffract from the edge of the shaded area of the cylinder without somehow crossing through some of the cylinder material, since the tangent at the surface is aligned with the direction of the incident ray.…”

Section: Conceptual Issues Arising From Eqnmentioning

confidence: 99%

Bringing the magic of light to remote areas where resources are scarce: beautiful demonstrations of interference patterns using laser pens and fibres

Mignard¹

2016

Phys. Educ.

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The training of physics teachers in remote areas in the developing world require s dedicated trainers (who typically are volunteers), as well as robust logistics. The latter must include the supply of equipment for experiments in the classroom. This task is greatly aided by the use of cheap, safe and readily available consumer goods that do not require local power supplies. In this paper, a simple experiment using a laser pointer pen and samples of hair as well as wire and transparent thin fibre is presented, reproducing a variant of Thomas Youngs' famed double slit experiment. The spread of the interference pattern as it projects itself on a screen is sufficiently large to catch the interest of students, and its orientation being perpendicular to that of the hair is also strikingly counterintuitive. The students are then encouraged to apply the simplified Fraunhofer equation to the various samples to find out the width of their hair. Ideally, these samples would also include calibrating materials like fibres and wires of known diameters, the use of which should give confidence in the model by confirming that it can predict the sample diameter. A fruitful discussion supported by diagrams can also be conducted on the differences that coul d be expected between a straight edge and a rounded edge, the latter throwing an unexpected challenge to the initial model. However, the use of a transparent fibre also clearly illustrate the limitations of this model, a perception that is amplified by the particularly wide and bright interference pattern that it produces. This mismatch between the model and the real system should prompt the students to further refine their description of the physical system and the resulting model. Throughout the session, their reasoning may be helped by encouraging them to produce diagrams showing the path of optical rays.

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“…In this methodology a CCD camera is used to record the Fraunhofer diffraction pattern of the wire and diameter is estimated from separation between successive diffraction minima. However, it is found that Classical Fraunhofer diffraction based diameter measurements result in an overestimation of wire diameters by one wavelength [4][5][6] . Also it is observed that accuracy of diameter measurement decreases for smaller diameters %-10% for d = 3 , due to more pronounced scattering effects.…”

Section: Introductionmentioning

confidence: 99%

“…Most of these optical methods, for measuring the diameters of thin opaque wires and fibers with high accuracy, are usually based on principles of optical diffraction 1-7 , polarization 8 , interferometry 9-10 , Optical microscopy 11 and laser beam scanning 12 . In past few decades optical diffractometry under Fraunhofer approximation has been widely used as an automated industrial inspection technique for dimension estimation [1][2][3][4][5][6][7] . In this methodology a CCD camera is used to record the Fraunhofer diffraction pattern of the wire and diameter is estimated from separation between successive diffraction minima.…”

Section: Introductionmentioning

confidence: 99%

“…As a result several methods to increase the resolution of diameter estimation under Conventional Fraunhofer diffraction using modified fringe spacing algorithms, wide-angular range of measurements, consideration of 3-D model of the object etc have been proposed in recent years 2,4,5,7,8 . However for most of the methods the diameters of wires under inspection range from 100-it is observed that errors in measurement through these methods increase greatly as diameter approaches the wavelength of light.…”

Section: Introductionmentioning

confidence: 99%

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A novel method for diameter estimation of small opaque objects using Fraunhofer diffraction

Vyas

Lolla

2010

Reflection, Scattering, and Diffraction From Surfaces II

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A novel optical method is proposed and demonstrated, for real-time dimension estimation of thin opaque cylindrical objects. The methodology relies on free-space Fraunhofer diffraction principle. The central region, of such tailored diffraction pattern obtained under suitable choice of illumination conditions, comprises of a pair of 'equal intensity maxima', whose separation remains constant and independent of the diameter of the diffracting object. An analysis of 'the intensity distribution in this region' reveals the following. At a point symmetrically located between the said maxima, the light intensity varies characteristically with diameter of the diffracting object, exhibiting a relatively stronger intensity modulation under spherical wave illumination than under a plane wave illumination. The analysis reveals further, that the said intensity variation with diameter is controllable by the illumination conditions. Exploiting these 'hitherto unexplored' features, the present communication reports for the first time, a reliable method of estimating diameter of thin opaque cylindrical objects in real-time, with nanometer resolution from single point intensity measurement. Based on the proposed methodology, results of few simulation and experimental investigations carried-out on metall is well-suited for high resolution on-line monitoring of ultrathin wire diameters, extensively used in micro-mechanics and semiconductor industries, where the conventional diffraction-based methods fail to produce accurate results.

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Three-dimensional diffraction of a thin metallic cylinder illuminated in conical incidence: application to diameter estimation

Cited by 6 publications

References 10 publications

White-light generation control with crossing beams of femtosecond laser pulses

White-light generation control with crossing beams of femtosecond laser pulses

Bringing the magic of light to remote areas where resources are scarce: beautiful demonstrations of interference patterns using laser pens and fibres

A novel method for diameter estimation of small opaque objects using Fraunhofer diffraction

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