The measurement of the surface cleanliness is a problem of great importance in many industrial and technological processes. Existing methods are based on laboratory procedures, they are not performed in real time, they cannot be automated, and usually they are restricted to a small portion of the sample. In this work we describe a new method for real time measurement of the amount of dirt deposited on a surface. It relies in the ablation of the dirt film by means of a short laser pulse and the subsequent measurement of the sound emitted. The intensity of the sound results proportional with the amount of dirt and provides a direct measurement of the cleanliness of the surface. The method requires a reference for calibration that was developed based in a uniform distribution of points printed on white paper or a transparent film. The point size and density can be easily modified providing a homogeneous, uniform and reproducible standard for the total amount of dirt measurement. Based on this method, we designed patented (P000101241-Argentina and 6.546.784 EEUU) and developed the first industrial instrument (ELMES) for on-line determination of the cleanliness degree of manufactured cold rolled steel plate bobbins.
A 3D modulated speckle pattern is stored in terms of the refractive index variation in a photorefractive BTO crystal. An image of a random diffuser is formed onto the crystal by means of a lens, which has a mask with two apertures. The intensity distribution received by the crystal creates a space charge field that indices through the linear electro- optic effect, a spatial variation of the refractive index. The angular selectivity involved in the volume nature of the registered speckle and its main features are analyzed. Besides, applications to optical processing are presented.
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