Removing Ambiguities in Surface Roughness Measurement

Abstract

Abstract.A new method is presented for the measurement df surface roughness in the range R. ~ 0·05-1 0 /lm. The data from a strongly defocused lowcontrast image of a rough surface is scanned, and the contrast value, C = (JJ(I> , is processed. A relatively low degree of spatial and temporal coherence, combined with a relatively high-image aperture and a detector aperture (which is much wider than the nominal speckle width of the corresponding highly coherent speckle pattern) led to important instrumental advantages, e.g., illumination by an incandescent lamp, simple photodetectors, short measuring times and simple, inexpensive, compact construction. The superposition of uniform intensity to the phase contrast structure, which leads to a strictly monotonic dependence of the measured contrast over a very wide range of the roughness values R. is of great importance. Practical measurements of metallic surface standards are reported and discussed, and the theoretical aspects of the superposition of uniform intensity are pointed out with the help of a new analytic expression for the stochastic contrast.

Using a zone model to incorporate the influence of geometry on polychromatic speckle contrast

“…Although the contrast of polychromatic speckle patterns has been used for numerous practical applications, [1][2][3][4][5][6][7][8][9][10][11][12][13] there are still situations, such as Fresnel diffraction, where simple and practical analytical expressions have not yet been derived. To fill this gap we have developed a simple geometrical model utilizing a Fresnel-zone analogy for quantitative estimation of the contrast.…”

“…The speckle contrast is of great interest in various industrial 1,2 and biomedical applications. [3][4][5][6][7][8][9][10] By measuring its value as a function of either tissue thickness or the coherence length of the light source, the absorption and scattering coefficients of the diffusive media can be derived.…”

Computer Analysis of Interferograms by Fitting Quadratic Forms

“…The computer analysis of interferograms [16][17][18][19][20][21] is performed by feeding the computer with the digitization data where they are fitted to mathematical formulae to deduce the useful information . The automatic reduction of interferograms not only allows accurate and rapid interpretation, but also offers the ability to work the surface further and to predict its optical performance .…”

Optische Mikroprofilometrie und Rauheitsmessung/ Optical microprofilometry and roughness measurement

“…Bild 18. Gerechnete Kontrastkurven nach der analytischen Kontrastformel aus[29] und[31] in Abhängigkeit vom quadratischen Mittenrauhwert R q der Autokorrelationsweite w a und dem Gleichlichtverhältnis t. Die Parameter des Gerätes und des Lichtes sind in[28; 29;31] angegeben. Die Kreise stellen die gemessenen Kontraste dar, die aus Bild 17 übertragen wurden.…”