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.
The acoustic energy responsive deformation of a workpiece surface is sensed in a contact-free manner by optical means using a laser which illuminates the surface at which deformation is expected. The reflection light energy is transmitted to an optical interferometer as previously shown in the art. The present improvement comprises the use of a multi-wavelength laser beam light and separating the light after passing through the interferometer into the distinct wavelengths. Each light signal corresponding to a specific wavelength is converted individually to an electrical signal, each electrical signal is rectified, and the plurality of rectified signals are then averaged in an electrical summing means.
A system for measuring the curvature of a surface includes a laser for emitting a beam of light to be incident upon the surface; a photodetector for detecting light reflected by the surface; a first stage for selectively moving the surface in a direction normal to the direction of the incident beam; a second stage for selectively moving the photodetector in a direction normal to the reflected beam; a sensor connected to the photodetector for detecting the displacement of the reflected beam relative to the photodetector.
A device for holding a measurement object e.g. in interferometers comprises a base plate and an attraction plate mounted on the base plate so as to attract the object placed on an upper surface of the attraction plate to the base plate together with the attraction plate by a vacuum applied via attraction grooves formed on the base plate and attraction passages perforated through the attraction plate. The upper surface of the base plate is formed as a reflection plane, and the attraction plate is made of a transparent material, so that Newton's rings generated by light reflected from the upper surface of the base plate and light reflected from the lower surface of the attraction plate can be observed from above the attraction plate.
An apparatus and method measures the roughness or some other surface dimension by transmitting a beam of light through a grating member at an angle of incidence relative to the grating member. The grating member has a plurality of parallel opaque bars and adjacent transparent bars. The beam of light forms a multiple line shadow pattern on the surface below the grating member formed by the shadows of the opaque bars of the grating member. A camera records the multiple line shadow pattern, and the recorded pattern is superimposed on a plurality of parallel, equally spaced scan lines oriented perpendicular to the shadow lines. The distances between the points at which adjacent shadow lines cross each respective scan line are measured to determine the roughness or some other surface dimension.
An array of a large number of low quality light collectors measure light generated by arrays of coherent light illuminators and rebounded from a target. The resulting data is utilized to derive the resulting speckle pattern which in turn is Fourier transformed to reconstruct the target image.
