Method, measuring arrangement and apparatus for optically measuring by interferometry the thickness of an object

A measuring arrangement for optically measuring by interferometry the thickness of an object featuring an external surface and an internal surface opposite with respect to the external surface, the measuring arrangement comprising:

• at least one radiation source emitting a low coherence beam of radiations composed of a number of wavelengths within a determined band;
• a first spectrometer analyzing a spectrum of the result of the interference between radiations that are reflected by the external surface without entering the object and radiations that are reflected by the internal surface entering the object;
• at least one optical probe which is connected by means of optical fiber lines to said at least one radiation source and to the spectrometer and is arranged in front of the object to be measured for directing the beam of radiations emitted by said at least one radiation source onto the external surface of the object and for collecting the radiations that are reflected by both the external and the internal surfaces of the object;
• a processing unit that calculates the thickness of the object as a function of the spectrum analyzed by the spectrometer;
• and
• an additional spectrometer coupled to said at least one optical probe,
• said first spectrometer being adapted to analyze the spectrum of the result of the interference between reflected radiations composed of a number of wavelengths within a first band and having a first central value, and
• said additional spectrometer being adapted to analyze the spectrum of the result of the interference between reflected radiations composed of a number of wavelengths within a second band and having a second central value.

An apparatus for optically measuring by interferometry the thickness of an object featuring an external surface and an internal surface opposite with respect to the external surface, the apparatus comprising:

• a radiation source emitting a low coherence beam of radiations composed of a number of wavelengths within a determined band;
• at least one spectrometer analyzing a spectrum of the result of the interference between radiations that are reflected by the external surface without entering the object and radiations that are reflected by the internal surface entering the object;
• an optical probe which is connected by means of optical fiber lines to the radiation source and to said at least one spectrometer, and is arranged in front of the object to be measured for directing the beam of radiations emitted by the radiation source onto the external surface of the object and for collecting the radiations that are reflected by both the external and the internal surfaces of the object;
• and
• a processing unit that evaluates the thickness of the object as a function of the spectrum analyzed by the at least one spectrometer;
• wherein the radiation source comprises:
• a first emitter which emits said low coherence beam of radiations as a first beam of radiations composed of a number of wavelengths within a first band having a first central value;
• at least a second emitter which emits said low coherence beam of radiations as a second beam of radiations composed of a number of wavelengths within a second band differing from the first band and having a second central value that is smaller than the first central value of the first band;
• and
• a commutator which alternatively enables to employ the first emitter or the second emitter as depending on the thickness of the object.