Browse Prior Art Database

Active Line Scan for High Resolution Microinterferometry

IP.com Disclosure Number: IPCOM000116838D
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Wagner, D: AUTHOR

Abstract

Disclosed is a method which in a scanning interferometer provides highest resolution in the x-y-direction, a big measuring range in the z-direction and unlimited accuracy of the interferometer by automatically and quickly focusing over the line scan and measuring the displacement of the objective. This method solves the two major problems of high resolution microinterferometry, its unambiguity within a range reduced to &lambda./2 in the z-direction and the low depth of focus of the high resolution objective.

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Active Line Scan for High Resolution Microinterferometry

      Disclosed is a method which in a scanning interferometer
provides highest resolution in the x-y-direction, a big measuring
range in the z-direction and unlimited accuracy of the interferometer
by automatically and quickly focusing over the line scan and
measuring the displacement of the objective.  This method solves the
two major problems of high resolution microinterferometry, its
unambiguity within a range reduced to &lambda./2 in the z-direction
and the low depth of focus of the high resolution objective.

      There are known image forming microinterferometers and scanning
microinterferometers, the image forming microinterferometers using a
TV camera and the scanning microinterferometers using a laser
scanner.  Whereas the line frequency of a TV camera is very high (15
625 Hz), the line frequency of most the laser scanners is in the 100
Hz range and thus distinctly below the frequency of quick
displacement elements like e.g., piezo translators moving microscope
objectives with a frequency of > 5 kHz.

      Todays' autofocus systems focus high resolution objectives with
an accuracy < 100 nm.  This should allow to keep an objective in
focus during a scan, even if the object is not flat, and assures the
highest resolution during the entire line scan.  This result may
however
not be obtained with a TV camera.

      The coherence length of a normal gas laser is approximately 30
cm.  Withi...