Specular Reflection Of Light Research Articles

Residual stress characterization during laser-based Directed Energy Deposition using in-situ digital image correlation based on specular light reflection on as-built surfaces of thin walls

Residual stresses present one of the major challenges within additive manufacturing as they lead to part distortion and cracking, production issues, scrapped parts and mechanically underperforming components. The current work presents a method to determine full-field residual stress information by deploying in-situ Digital Image Correlation during the Directed Energy Deposition process of thin walls. In an attempt not to disturb the process to apply the typical ‘speckle pattern’, the correlation analysis is based on the specular light reflection of active lighting on the as-built surface of thin walls under construction. This approach allows the continuous monitoring of the thermally induced stresses, both during the actual deposition process as well as during the subsequent cooldown phase. The method presents significant time-savings while providing maximized insight in the formation process of residual stresses. The manuscript presents the used test configuration, initial proof-of-concept results along with an accuracy estimation of the used method.

Why Is the Angle of Incidence Equal to the Angle of Reflection? An Activity

Students are often introduced to optics in their middle school years. The initial topics that are introduced through their lessons are laws of reflection and refraction of light. In the law of reflection, students do not often question why the angle of incidence is equal to the angle of reflection and why a light ray should follow this specific path. Here we encourage students to question this result and provide an exercise to facilitate instruction regarding specular reflection of light.

Ceramic technology. How to investigate surface finishing

Surface treatment techniques, that is, smoothing and burnishing, help to define the cultural, traditional, and economical state of an ancient society. They prove artistic feelings combined with practical skills were used to obtain more attractive and highly functional objects. This paper aims to prepare the reader to investigate ceramic surfaces and discern between different treatments. Interpretation of the finishing techniques is based mainly on a wide variety of surface topography. Both treatments plastically deform the surface and tend to diminish its roughness, but the results are strikingly different. A smoothed surface has still large irregularities and a dull or matte appearance due to the diffuse reflection of light. A burnished surface has only small-sized irregularities and is glossy/lustrous due to specular reflection of light. Smoothing slightly aligns the platy minerals only at the very surface, whereas, burnishing may create two separate individual levels: A burnish peel and a subsurface layer. The differences are evidenced by all applied analytical methods, such as macroscopy, optical microscopy, electron microprobe, scanning electron microscopy, and vertical scanning interferometry.

The dependence of ellipsometric parameters Δ and Ψ on refractive index of superficial film

The ellipsometrical analysis of external specular reflection of light on non-absorbing superficial films allows us to know factors which influence the ellipsometric measurement of the analyzed system. For optical non-absorbing superficial films the curves Δ = f(Ψ) are closed, the curves Δ = f(df) and Ψ = f(df) are periodical, while the curves Δ = f(nf) and Ψ = f(nf) are pseudo-periodic. Observations on the dependence of the ellipsometric parameters Δ and Ψ on nf are presented.

Spectroscopy of Plasmon-Excitons in Semiconductor-Metal Nanostructures

The results of the theory considering mixed plasmon-excitonic modes and their spectroscopy are presented. The plasmon-excitons are formed owing to strong Coulomb coupling between quasi-two-dimensional excitons of a quantum well and dipole plasmons of nanoparticles. The effective polarizability associated with a nanoparticle is calculated in a self-consistent approximation taking into account the local field determined by in-layer dipole plasmons and their image charges due to the excitonic polarization of a near quantum well. The spectra of elastic scattering and specular reflection of light are investigated in cases of a single silver nanoparticle and a monolayer of such particles situated in close proximity to a quantum well GaAs/AlGaAs. The optical spectra show a two-peak structure with a deep and narrow dip in the resonant range of plasmon-excitons. Propagation of plasmon-excitonic polaritons is discussed for periodic superlattices whose unit cell consists of a quantum well and a layer of metal nanoparticles. The superradiance regime originating in the Bragg diffraction of plasmon-excitonic polaritons by the superlattice is investigated. It is shown that the broad spectrum of plasmonic reflection depending on the number of unit cells in a superlattice also has a narrow dip at the exciton frequency.

Спектроскопия плазмон-экситонов в наноструктурах полупроводник-металл

AbstractThe results of the theory considering mixed plasmon-excitonic modes and their spectroscopy are presented. The plasmon-excitons are formed owing to strong Coulomb coupling between quasi-two-dimensional excitons of a quantum well and dipole plasmons of nanoparticles. The effective polarizability associated with a nanoparticle is calculated in a self-consistent approximation taking into account the local field determined by in-layer dipole plasmons and their image charges due to the excitonic polarization of a near quantum well. The spectra of elastic scattering and specular reflection of light are investigated in cases of a single silver nanoparticle and a monolayer of such particles situated in close proximity to a quantum well GaAs/AlGaAs. The optical spectra show a two-peak structure with a deep and narrow dip in the resonant range of plasmon-excitons. Propagation of plasmon-excitonic polaritons is discussed for periodic superlattices whose unit cell consists of a quantum well and a layer of metal nanoparticles. The superradiance regime originating in the Bragg diffraction of plasmon-excitonic polaritons by the superlattice is investigated. It is shown that the broad spectrum of plasmonic reflection depending on the number of unit cells in a superlattice also has a narrow dip at the exciton frequency.

Gloss Evaluation of Hairline-Finished Metal Surface Using Patterned Area Illumination Method: Relationship between Gloss Evaluation and Surface Roughness for the Estimation of Surface Roughness

The gloss of a metal surface is an important aspect for product quality evaluation. In general, gloss is influenced by specular reflection of light on a metal surface. Therefore, evaluating the specular reflection is almost the same as evaluating the gloss. We propose a method that uses patterned area illumination to evaluate specular reflection. In specular reflection, the angle of incidence equals the angle of reflection. Consequently, when light (ray) of the area illumination, which has a striped pattern, are projected on a glossy metal surface, a striped pattern forms on the reflected image as a mirror-like reflection, and the sharpness of the striped pattern of the image provides information about the specular reflection on the surface. This characteristic is applied to a metal with a hairline surface finish. A hairline surface presents different glossiness at different viewpoints. When the direction of the striped pattern of illumination is changed, the sharpness of striped pattern on the reflected image varies owing to the surface roughness of the hairline finish. Therefore, we can evaluate the glossiness in various directions by rotating the pattern. The rough relationships between gloss evaluation value and surface roughness were indicated in our study. In order to make the relationship between gloss evaluation and surface roughness for the estimation of surface roughness, we had tried the comparison for the gloss evaluation value and the surface roughness. The more precise relationship for seven directions on hairline-finished metal surface was measured. This report describes the results and considers the possibility of estimation of surface roughness by the gloss evaluation value.

Removing sun glint from optical remote sensing images of shallow rivers

AbstractSun glint is the specular reflection of light from the water surface, which often causes unusually bright pixel values that can dominate fluvial remote sensing imagery and obscure the water‐leaving radiance signal of interest for mapping bathymetry, bottom type, or water column optical characteristics. Although sun glint is ubiquitous in fluvial remote sensing imagery, river‐specific methods for removing sun glint are not yet available. We show that existing sun glint‐removal methods developed for multispectral images of marine shallow water environments over‐correct shallow portions of fluvial remote sensing imagery resulting in regions of unreliable data along channel margins. We build on existing marine glint‐removal methods to develop a river‐specific technique that removes sun glint from shallow areas of the channel without over‐correction by accounting for non‐negligible water‐leaving near‐infrared radiance. This new sun glint‐removal method can improve the accuracy of spectrally‐based depth retrieval in cases where sun glint dominates the at‐sensor radiance. For an example image of the gravel‐bed Snake River, Wyoming, USA, observed‐versus‐predicted R2 values for depth retrieval improved from 0.66 to 0.76 following sun glint removal. The methodology presented here is straightforward to implement and could be incorporated into image processing workflows for multispectral images that include a near‐infrared band. Copyright © 2016 John Wiley & Sons, Ltd.

Remote Sensing of the EnviSat and Cbers-2B satellites rotation around the centre of mass by photometry

During 2013–2015 the photometric observations of the EnviSat satellite, which became space debris after the failure in April 2012 in low Earth orbit, were performed. The rotation pole position and slow change in sidereal rotation period were updated on the basis of analysis of specular glints observed in 222 light curves using reduction of synodic periods. Apparently, there are minor oscillations of the rotation pole near the normal to the orbital plane. The sense of the EnviSat’s spinning is opposite to the sense of its orbital rotation. The sidereal period is best approximated by the second-order polynomial: Psid(sec)=0.000021534·T2+0.04936003·T+121.18195 where T is measured in days from the beginning of 2013. This method being applied to another representative of space debris, namely the Cbers-2B satellite, has shown a similar result: there is not precise solution for the rotation pole either as it undergoes oscillations with various time scale from several hours to several months. In 2014, the spin axis made the 10° angle with the normal to the orbital plane while the sense of spinning is direct in this case, i.e. coincides with the sense of orbital rotation. The sidereal period is best approximated by the following expression: Psid(sec)=0.000029543·T2+0.08094931·T+81.31775 where T is measured in days starting from March 10, 2014. This method allows of controlling slow changes in the spatial orientation of the rotation axis of the satellites in which specular reflection of light from flat faces of the surface is inherent.

The Effect of Sunglint on Benthic Habitats Mapping in Pari Island Using Worldview-2 Imagery

Sunglint is a specular reflection of light from water surfaces that may cause misclassification and poor accuracy for benthic habitats mapping. The aim of this research was to investigate sunglint intensity for each benthic habitats and compared the accuracy result before and after sunglint correction from worldview-2 imagery. Hedley method and analysis coefficient of variation (COV) was used to estimate and remove the glint radiance component, while Mahalanobis distance was used to classify before and after sunglint correction from those imagery. The result showed that the average of sunglint intensity on benthic habitats was 38,9%. The highest sunglint intensity effect found in coral reef class (44%) and the lowest one in sand class (34%). The overall accuracy before and after sunglint correction were 53% and 60%. Sunglint correction well to do in reducing the effect of sunglint and increase the overall accuracy till 7%.

Spectroscopic sensing of reflection optical activity in achiral AgGaS₂.

Optical activity is a fundamental effect of electrodynamics that was discovered more than 200 years ago. While optical activity is typically recognized by the rotation of the polarization of light as it propagates through a bulk medium, in certain configurations, the specular reflection of light on the surface of a material is also sensitive to its optical activity. Here, we show that the ellipsometric analysis of the light reflected at the surface of a gyrotropic but achiral crystal of AgGaS(2) allows the spectroscopic determination of its optical activity above the bandgap, where transmission methods are not applicable. This is the first clear spectroscopic determination of reflection optical activity in a crystal, and the values obtained are, to the best of our knowledge, the largest ever reported for a natural material. We also demonstrate that normal incidence transmission and reflection measurements probe different aspects of optical activity.

The Ellipsometrical Analysis of External Reflection of Light on Superficial Films on Solid Substrates

The ellipsometrical analysis of the external specular reflection of light on nonabsorbing superficial films allows us to know factors which influence the ellipsometric measurement of the analyzed system. For optical nonabsorbing superficial films the curves =f(d_f) and =f(d_f) are periodical, while the curves =f() are closed. The paper presents observations on the dependence of the ellipsometric parameters  and  on d_f. The analysis of the periodicity of these curves allows us to correctly determine the film thickness for thicknesses greater than d_min. The value of d_min depends on the refractive index n_f of the surface film, the incidence angle φ0 and the wavelength λ of the incident radiation. The dependence of d_min on n_f, φ0 and λ is analyzed. From the curve shape we can draw conclusions with respect to the domain of small errors, allowing us to correctly determine the thickness and refraction index of superficial films.

Investigation of starburst phenomenon using ray tracing for touch screen panels

We investigate the effect of the metal pattern shape (i.e., square, hexagonal, and random grids) on the starburst phenomenon of touch screen panels (TSPs) based on opaque metallic grids. It is demonstrated that a standalone random metal grid can suppress the starburst phenomenon to a great extent. By way of ray tracing simulation, we have found that specular reflection of light on the gentle slope of the patterned edges of metallic grids contributes to the generation of starburst patterns. It is also addressed that employing a light-absorbing material and increasing metal grid spacing can reduce the intensity of starburst patterns.

Enhancing stereo matching performance by colour normalisation and specularity removal

A method to enhance the performance of stereo matching is presented. The position of the specular light reflection on an object surface varies due to the change in the position of the camera, light source, object or all combined. Additionally, there may be situations exhibiting a colour shift owing to a change in the light source chromaticity or camera white balance settings. These variations cause misleading results when stereo matching algorithms are applied. In this reported work, a single-image-based statistical method is used to normalise source images. This process effectively eliminates non-saturated specularities regardless of their positions on the object. The effect of specularity removal is tested on stereo image pairs.

Sun Glint Correction of High and Low Spatial Resolution Images of Aquatic Scenes: a Review of Methods for Visible and Near-Infrared Wavelengths

Sun glint, the specular reflection of light from water surfaces, is a serious confounding factor for remote sensing of water column properties and benthos. This paper reviews current techniques to estimate and remove the glint radiance component from imagery. Methods for processing of ocean color images use statistical sea surface models to predict the glint from the sun and sensor positions and wind data. Methods for higher resolution imaging, used in coastal and shallow water mapping, estimate the glint radiance from the near-infrared signal. The effects of some current methods are demonstrated and possibilities for future techniques are briefly addressed.

Gloss Evaluation Method for Metal Surface with Hairline Using Patterned Area Illumination

Gloss evaluation of a metal surface is important for the quality as the product. In general, gloss of a metal surface is influenced by specular reflection of light on the surface. Therefore to evaluate the specular reflection is almost the same as the evaluation of the gloss. We propose the method to evaluate the specular reflection using patterned area illumination. In the specular reflection, the angle of incidence is equal to the angle of reflection. Consequently when lights (rays) of the area illumination which has a stripe pattern are projected to a glossy metal surface, the stripe pattern occurs on the reflection image by the mirror-like reflection and the sharpness of the stripe pattern of the image has information of the specular reflection on the surface. This character is applied for the metal surface with hairline. The metal surface with hairline has different gloss feeling at different point of view. When the direction of the stripe pattern of the illumination is changed, the sharpness of stripe pattern on the reflection image varies owing to the surface roughness of hairline. Therefore we can evaluate the glossiness for various directions by rotating the stripe pattern. This paper shows the availability of the proposed method through the experiment.

Gloss Evaluation Method for Metal Surface with Hairline Using Patterned Area Illumination

Gloss evaluation of a metal surface is important for the quality as the product. In general, gloss of a metal surface is influenced by specular reflection of light on the surface. Therefore to evaluate the specular reflection is almost the same as the evaluation of the gloss. We propose the method to evaluate the specular reflection using patterned area illumination. In the specular reflection, the angle of incidence is equal to the angle of reflection. Consequently when lights (rays) of the area illumination which has a stripe pattern are projected to a glossy metal surface, the stripe pattern occurs on the reflection image by the mirror-like reflection and the sharpness of the stripe pattern of the image has information of the specular reflection on the surface. This character is applied for the metal surface with hairline. The metal surface with hairline has different gloss feeling at different point of view. When the direction of the stripe pattern of the illumination is changed, the sharpness of stripe pattern on the reflection image varies owing to the surface roughness of hairline. Therefore we can evaluate the glossiness for various directions by rotating the stripe pattern. This paper shows the availability of the proposed method through the experiment.

Roughness of pigment coatings and its influence on gloss

A robust method is used for analyzing roughness at a wide range of lateral length scales. The method is based on two-point correlation where both the amplitude and lateral spacing of surface heights are considered when determining the roughness. Atomic force microcopy and confocal optical microscopy images were captured for a set of pigment-coated samples. The effects of sampling interval, image size and filtering on surface roughness were studied. Isotropy and periodicity of roughness were determined by analyzing the angular distribution of the correlation length ( T) and the autocorrelation function (ACF). A clear dependence of root mean square (RMS) roughness ( σ) on T was established for randomly distributed surfaces. By taking into account the σ– T dependence it was possible to obtain σ for various length scales for each sample and thus attaining the most relevant σ for a certain surface function, which in this study was specular reflection of light (gloss). The roughness analysis showed that a small amount of DPP coating was sufficient to completely cover and change the surface of the substrate, while kaolin coatings gave a different response.

Diffraction mechanism of specular reflection of light from photonic crystals

The spectra of specular reflection and diffraction of light for a resonant two-dimensional photonic crystal consisting of semiconductor cylinders embedded in a dielectric matrix, as well as the exciton-polariton band structure of this crystal, are studied theoretically. It is shown that specular reflection of light from a photonic crystal can be considerably enhanced by diffraction in the photonic crystal and reflection from its inner boundary with vacuum.

Development of a Robust Photogrammetric Metrology System for Monitoring the Healing of Bedsores

AbstractA three‐camera close range photogrammetric system for robust and precise measurement of bedsores has been designed and constructed. MEDPHOS (MEDical PHOtogrammetric System) consists of three synchronised cameras with convergent optical axes. A light projector is fixed in the centre of the rig that holds the cameras. A special dot pattern is projected onto the surface to be measured, to compensate for the lack of natural texture on the wound surface. The proposed algorithm consists of the following steps: the cameras and projector are calibrated so that all interior and exterior parameters are known; tailored image segmentation procedures are developed and applied for the detection of the projected pattern dots from the uneven background of the images using morphologic operators; and watershed transformation is used to tackle the problem of overlapping pattern dots. To reduce the effects of non‐uniform illumination and specular reflection of light due to humidity (often the case with wounds), a homomorphic transformation is developed and applied to the images. After segmentation of the images, a connected‐component labelling procedure is used to establish the points for matching. The centroids of these components were precisely calculated. Intensity‐based image matching has been tested without yielding satisfactory results due to the significant deviation from the Lambertian reflection assumption used for solving the correspondence problem. This problem is reliably solved by developing a new algorithm based on geometric constraints that allow feature‐based matching and do not need approximate values of the location of the targets in the images. This robust three‐focal constraint is found to be very effective for matching provided the necessary conditions for the system configuration are met. Auxiliary photometric constraints together with the calibrated projector (which is treated like an active camera) also serve as additional sources of information for reducing the number of remaining ambiguities and checking the consistency of the results. Almost all of the required biometric information can be obtained rapidly, robustly and easily using MEDPHOS. Experimental results showed the effectiveness of the proposed technique.