Measurement of surface roughness
First Claim
1. A method for measuring surface roughness, surface waviness, surface cracks, or any irregularities or flatnesses in a surface, including the following steps:
- generating a spatially coherent polychromatic light having at last two different wavelengths and directing the polychromatic light at an optically rough surface in order to illuminate the same;
analyzing intensity variations in two speckle patterns formed at a light field scattered from the optically rough surface due to the two different wavelengths of the polychromatic light; and
defining and evaluating a difference between intensities of the two speckle patterns as a function of surface roughness of the optically rough surface.
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Abstract
A method and apparatus for measuring surface roughness, waviness, cracks or any irregularities or flatnesses in a surface utilizing statistical properties of dichromatic speckle patterns. In practice surface roughness is normally measured utilizing standard profile measuring devices. However, these instruments are not efficient in practice in view of their slowness for effecting measurements. The present invention provides an improved method of measuring surface roughness including the following steps; generating a spatially coherent polychromatic light having at least two wavelengths and directing the light at an optically rough surface in order to illuminate the same; analyzing intensity variations in two speckle patterns formed at a plane due to two wavelengths of the polychromatic light; and defining and evaluating a difference between intensities of the two speckle patterns as a function of surface roughness of the optically rough surface.
38 Citations
9 Claims
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1. A method for measuring surface roughness, surface waviness, surface cracks, or any irregularities or flatnesses in a surface, including the following steps:
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generating a spatially coherent polychromatic light having at last two different wavelengths and directing the polychromatic light at an optically rough surface in order to illuminate the same; analyzing intensity variations in two speckle patterns formed at a light field scattered from the optically rough surface due to the two different wavelengths of the polychromatic light; and defining and evaluating a difference between intensities of the two speckle patterns as a function of surface roughness of the optically rough surface. - View Dependent Claims (2, 3, 4)
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5. An apparatus for measuring surface roughness, surface waviness, surface cracks or any irregularities or flatnesses in a surface, the apparatus comprising a laser adapted to generate a spatially coherent polychromatic light having two different wavelengths which is directed at an optically rough surface of an object situated in an object plane;
- an aperture placed between the laser and the optically rough surface of the object to be tested, such that the polychromatic light from the laser passes through the aperture and impinges on the optically rough surface;
separate means being provided in a specular direction at a scattered light plane separated from the object plane by a predetermined distance to analyze a dichromatic speckle pattern produced at the plane by light from each of said two different wavelengths scattered from the optically rough surface. - View Dependent Claims (6, 7, 8, 9)
- an aperture placed between the laser and the optically rough surface of the object to be tested, such that the polychromatic light from the laser passes through the aperture and impinges on the optically rough surface;
Specification