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Abstract

Method, measuring arrangement (23;26;27) and apparatus (1) for optically measuring by interferometry the thickness of an object (2) having an external surface (16) and an internal surface (17) opposite with respect to the external surface. A low coherence beam of radiations (I) is emitted, such beam being composed of a number of wavelengths within a band determined, by means of radiation sources (4a,4b;4c,4d;4ef) which can alternatively employ at least two different radiation beams belonging to differentiated bands, as depending on the thickness of the object, or a single wide band radiation source. The radiation beam is directed onto the external surface of the object by means of an optical probe (6). The radiations (R) that are reflected by the object are caught by means of the optical probe. By means of spectrometers (5;5a,5b;5d,5e;5f,5g) it is possible to analyze the spectrum of the result of the interference between radiations (R1) that are reflected by the external surface without entering the object and radiations (R2) that are reflected by the internal surface entering the object; and the thickness of the object is determined as a function of the spectrum provided by the spectrometers. The two spectrometers can be alternatively used for radiations belonging to each of said differentiated bands.

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