Method for the non-contact rapid and accurate acquisition of the surface topology of objects
First Claim
1. A method of profiling a surface of an object, which comprises the steps of:
- a) placing an object in vicinity of an interferometer having interferometer arms and a translation stage, and transmitting a low coherent light signal from a light source with a mean wavelength λ
to the object;
b) varying an optical path in one of the interferometer arms with the translation stage;
c) receiving a resulting intensity-modulated interferometer signal with a photodetector having low pass characteristics and outputting photodetector output signals;
d) evaluating the photodetector output signals with an image processing system; and
e) extracting a depth of modulation of the interferometer signal by intensity-modulating the low coherent light source.
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Abstract
The method allows contact-less, precise and rapid measurement of the macroscopic shape of objects. The method is based on the Michelson-interferometer with the object mirror being replaced by the object to be measured. A low coherent light source is used. As either the reference mirror or the object is moved, an intensity modulation can be observed on the observation screen. The height information can be derived from determining the maximum depth of modulation in association with the movement. The determination of the depth of modulation has required full sampling of the modulation at a high sampling rate, or quasistatic movements. Therefore common methods are rather slow. The envelope of the modulation is directly extracted by modulating the light source synchronously to the modulation of the interference patterns and by using a solid-state imaging array which shows low pass characteristics in terms of time. The method allows to move the object or the reference mirror significantly faster than in conventional short coherent interferometers at a far lower sampling rate. If a light source cannot be modulated, the flux of light hitting the target or the sensitivity of the photodetector can be modulated instead.
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Citations
17 Claims
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1. A method of profiling a surface of an object, which comprises the steps of:
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a) placing an object in vicinity of an interferometer having interferometer arms and a translation stage, and transmitting a low coherent light signal from a light source with a mean wavelength λ
to the object;b) varying an optical path in one of the interferometer arms with the translation stage; c) receiving a resulting intensity-modulated interferometer signal with a photodetector having low pass characteristics and outputting photodetector output signals; d) evaluating the photodetector output signals with an image processing system; and e) extracting a depth of modulation of the interferometer signal by intensity-modulating the low coherent light source. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A method of profiling a surface of an object, which comprises the steps of:
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a) placing an object in vicinity of an interferometer having interferometer arms and a translation stage, and transmitting a non-modulated low coherent light signal with a mean wavelength λ
from a light source to the object;b) varying an optical path in one of the interferometer arms with the translation stage; c) receiving a reflected signal with a photodetector having low pass characteristics and outputting photodetector output signals; d) evaluating the photodetector output signals with an image processing system; and e) extracting a depth of modulation of the interferometer signal by modulating one of a flux of light which hits the photodetector, and a sensitivity of the photodetector.
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Specification