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Conoscopy offers certain advantages
over interferometry, triangulation and dynamic focusing,
for point-by-point distance mapping.
Interferometry can only be used to
measure optically flat and specularly reflecting surfaces.
Additionally, because interferometry compares two beams,
it requires a highly coherent laser source and a very
stable optical environment making it bulky, expensive
and temperature sensitive. In contrast, Conoscopy measures
both diffuse and reflective surfaces, yet does not require
an optically rigid system.
Triangulation methods measure distance
in the following way:
A collimated laser beam is shot at an object at a given
angle, and the reflected beam then travels through a
lens, creating a spot on a detector. Using triangulation,
distance is determined by measuring the position of
this spot on the detector. This puts a limit on measurement
of high aspect ratio structures, due to beam obscuration.
Although temperature sensitive, triangulation is not
co-linear so it does not require a rigid, expensive
optical system. Nevertheless, Conoscopy, while simpler
and more reliable than triangulation, has a better ratio
of depth-of-field to stand-off distance and can measure
angles close to normal.
Dynamic focusing measures distance
by determining the best focus of a camera, and thus
the distance of the object. This method uses moving
parts and is dependent upon feedback. It is more expensive,
less reliable and requires more sophisticated image
processing than Conoscopy.
White light interferometry has been the leading technology
in the laboratory world for years. It is used for measuring
surfaces to the highest degree of precision. The main
industrial application of white light interferometry
is in high precision measurement of semiconductors.
However, in order to achieve the desired precision,
the measurements must be performed in well-controlled
environments, a requirement which makes it extremely
expensive. In comparision, Conoscopy provides precision
measurement even under harsh environmental conditions,
it costs significantly less and is suitable for a wider
variety of industrial sites than white light interferometry.
Last Update:
October 28, 2007
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