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Browse Prior Art Database

Fast And Precise Analysis of Varying Interference Patterns

IP.com Disclosure Number: IPCOM000102466D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 96K

Publishing Venue

IBM

Related People

Elsner, G: AUTHOR [+2]

Abstract

Disclosed is a new method of detecting light interference patterns, which can be employed in conjunction with picture analysis techniques for contactless surface structure (roughness) measurements.

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This is the abbreviated version, containing approximately 57% of the total text.

Fast And Precise Analysis of Varying Interference Patterns

       Disclosed is a new method of detecting light interference
patterns, which can be employed in conjunction with picture analysis
techniques for contactless surface structure (roughness)
measurements.

      Normally, an object is illuminated by means of coherent light
which is reflected with different phases depending on the surface
structure.  Superposition of the reflected and the incident light
yields an interference pattern of an intensity that can be recorded
and analyzed.  For high resolution, standard techniques use three
such patterns which are sequentially recorded, each phase-shifted by
2 f/3.  This leads to stabilization problems during recording.

      The presently described method avoids instability effects by
simultaneously recording the three patterns by means of a phase grid
combined with a standard CCD TV sensor (Fig. 1).  As shown in Fig. 1,
linearly polarized light passes through a g/4 plate, so that the
object is illuminated with circularly polarized light.  Superposition
of the reflected and the incident light yields linearly polarized
light where the phase information, rather than intensity variations,
may be derived from the different orientation of polarization.  This
information is transformed by a polarization filter into intensity
modulations which are detectable by the CCD array.  A phase grid
preceding the polarization filter separates interference patterns of
...