Scatterometer of visible light for 2D rough surfaces (original) (raw)
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Assessment of Scattering of Plane Waves on Optically Illuminated Area of Rough Surface
Progress In Electromagnetics Research B
In this paper, a new robust computational method that applies the geometrical theory of diffraction (GTD) in conjunction with the ray tracing (RT) technique is developed to evaluate the electromagnetic scattering pattern due to a plane wave incident on a rough surface of quite arbitrary statistical parameters. The Fresnel reflection model is applied under the assumption of arbitrary electrical and optical properties of the rough surface material to obtain the scattering patterns for both the power reflected to the upper half-space and the power transmitted into the medium covered by the rough surface. Also the polarization of the plane wave primarily incident on the rough surface is taken into consideration. The algorithm developed in the present work accounts for multiple bounces of an incident ray and, hence, it can be considered arbitrary higher-order GTD-RT technique. The accuracy of the obtained results is verified through the comparison with the experimental measurements of the scattering pattern of a light beam incident on rough sheets with specific statistical properties. Also, some of the obtained results are compared to other published results using the geometrical optics (GO) and the second-order Kirchhoff's approximation. The numerical results of the present work are concerned with investigating the dependence of the scattering pattern on the surface roughness, refractive index, angle of incidence, and the resolution of the geometric model of the rough surface. Also, it is shown that for limited resolution of the rough surface model, the accuracy of the calculated scattered field depends on the angle of incidence of the primary beam and the surface roughness.
Treatment of light scattering by a rough surface in terms of its three-dimensional spectrum
Proceedings of SPIE, 1993
It is demonstrated that scattering by a rough surface can be described in terms of its 3-D spectrum and the coherent transfer function, which was first developed to describe the process of imaging.The three-dimensional coherent transfer function for confocal imaging is presented for a high-angle theory. From this an effective transfer function for imaging of rough surfaces is developed, based on the Kirchhoff approximation. It is described how confocal imaging can be used to investigate various scattering mechanisms, and can be used for reconstruction of surface profiles in the Kirchhoff approximation.
Measuring the Reflection Matrix of a Rough Surface
Applied Sciences
Phase modulation methods for imaging around corners with reflectively scattered light required illumination of the occluded scene with a light source either in the scene or with direct line of sight to the scene. The RM (reflection matrix) allows control and refocusing of light after reflection, which could provide a means of illuminating an occluded scene without access or line of sight. Two optical arrangements, one focal-plane, the other an imaging system, were used to measure the RM of five different rough-surface reflectors. Intensity enhancement values of up to 24 were achieved. Surface roughness, correlation length, and slope were examined for their effect on enhancement. Diffraction-based simulations were used to corroborate experimental results.
Journal of the Optical Society of America A, 2008
In this work it is shown theoretically and examined experimentally that the measurement of coherently transmitted or reflected monochromatic light intensity from a randomly rough interface as a function of incident angle provides the height distribution on the interface. It is also shown that the spectrum of coherently transmitted or reflected light from a rough interface is modified and the modified spectrum yields the height distribution. The experimental results obtained by applying both methods, in transmission and reflection, on rough surfaces prepared by roughening the sheet glasses by powders of different grain sizes are quite consistent. In addition, the effect of the surrounding medium's refractive index on the roughness measurement is studied by immersing the samples into liquids of different refractive indices. Also, the application range and limitations of the introduced methods are discussed.
Device for Measuring BDF – Spatial - Spectral Light - Scattering Properties of Surfaces
DAAAM INTERNATIONAL SCIENTIFIC BOOK 2012, 2012
Device for measuring spectral-spatial distribution of light dispersed by surfaces is presented. These data are necessary for calculations and computer simulation of reflectors, liquid crystal displays, clothes, paints, and other objects and materials with non trivial light-scattering characteristics. The modern systems of computer graphics also need such data for accurate simulation of light propagation. The direct measurements are the more reliable methods to obtain these data, but this task is not easy. Conception proposed by authors allowed to realize the effective device, which is used for numerous practical tasks.
New Scatterometer for Spatial Distribution Measurements of Light Scattering from Materials
Measurement Science Review, 2012
A new scatterometer is composed of two ellipsoidal mirrors of revolution and an optical detection system. It enables us to absolutely measure diffuse reflectance and transmittance and to measure the spatial distribution of light scattering from almost all materials. The optical detection system has been developed both to measure total photo-intensity using a photodiode and to capture the imaging data using a CCD camera. This results in faster, more complete and often more accurate measurements than can be achieved with traditional goniometric methods and integrated sphere methods. The absolute total integrated reflectance and transmittance of well-known samples were measured and the spatial distribution of light scattering from a diffraction grating was captured and evaluated.
Optical diagnostics of slightly rough surfaces
Applied Optics, 1992
The relationship between the statistical structure parameters of a rough surface and the associated correlation parameters of a scattered field is used to develop a method for rough-surface diagnostics. The treatment is based on the model of a random phase object with an inhomogeneity phase dispersion C' < 1. The proposed diagnostic methods are applicable to surfaces with a roughness period comparable to the radiation wavelength employed and the surfaces of a thin plane-parallel plate. The sensitivity limit of the methods in measuring the standard deviation of surface-roughness element heights is 0.003 pum.
Diffuse and Specular Reflectance from Rough Surfaces
Applied Optics, 1998
We present a reflection model for isotropic rough surfaces that have both specular and diffuse components. The surface is assumed to have a normal distribution of heights. Parameters of the model are the surface roughness given by the rms slope, the albedo, and the balance between diffuse and specular reflection. The effect of roughness on diffuse reflection is taken into account, instead of our modeling this component as a constant Lambertian term. The model includes geometrical effects such as masking and shadowing. The model is compared with experimental data obtained from goniophotometric measurements on samples of tiles and bricks. The model fits well to samples with very different reflection properties. Measurements of the sample profiles performed with a laser profilometer to determine the rms slope show that the assumed surface model is realistic. The model could therefore be used in machine vision and computer graphics to approximate reflection characteristics of surfaces. It could also be used to predict the texture of surfaces as a function of illumination and viewing angles.
Investigation of light scattering from rough periodic surfaces --- numerical solutions
Optics and Laser Technology, 1992
The Beckmann scalar scattering model based on the Kirchhoff approximation was used to investigate the scattering of light from periodic surfaces whose roughness amplitude is comparable to, and greater than, the illumination wavelength. Solutions by numerical integration were obtained for surfaces of different profiles and of different roughnesses. It was found that the scattering patterns from these surfaces were very different at large roughness amplitudes. As the incident angle was varied on a given surface, it was also observed that the intensity of any individual diffraction order oscillated and the degree of oscillation was directly related to roughness. By utilizing this property, a new procedure could be developed for surface roughness assessment.