Digital refinement of interferograms obtained by double-pulse interferometry and automatic sign correction of phase gradients after FFT evaluation

Wolfgang Steinchen; Peter Maeckel; J. Nickel; Frank Voessing; Gerhard Kupfer

doi:10.1117/12.364246

21 September 1999 Digital refinement of interferograms obtained by double-pulse interferometry and automatic sign correction of phase gradients after FFT evaluation

Wolfgang Steinchen, Peter Maeckel, J. Nickel, Frank Voessing, Gerhard Kupfer

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Proceedings Volume 3824, Optical Measurement Systems for Industrial Inspection; (1999) https://doi.org/10.1117/12.364246
Event: Industrial Lasers and Inspection (EUROPTO Series), 1999, Munich, Germany

Abstract

Applying the pulse laser to speckle methods, nonuniformities of the laser beam profiles and the intensities between each laser pulse have unpleasant consequences on the intensity distribution of the recorded images and following on the expected fringes of the corresponding subtractive result. This contribution introduces a computer based technique for compensating this technical and physical problem, so that the fringe quality is improved, even if the homogeneity of the laser beam profiles is on such low level, that the conventional (subtractive) technique fails. The solution is based on algorithms, which refines each intensity distribution and is comparable with the known shading correction. After this refinement the interferogram can be processed by the well known Fourier transform evaluation of the relative phase distribution. Applying the FFT, practical problems arise when it comes to the step of automatic sign corrections. The contribution will discuss an approach of automatic sign correction. The methods for refinement and automatic sign correction following the Fourier transform evaluation is explained in detail and demonstrated on selected interferograms.

Citation Download Citation

Wolfgang Steinchen, Peter Maeckel, J. Nickel, Frank Voessing, and Gerhard Kupfer "Digital refinement of interferograms obtained by double-pulse interferometry and automatic sign correction of phase gradients after FFT evaluation", Proc. SPIE 3824, Optical Measurement Systems for Industrial Inspection, (21 September 1999); https://doi.org/10.1117/12.364246

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KEYWORDS

Speckle

Fourier transforms

Pulsed laser operation

Interferometry

CCD cameras

Bandpass filters

Image processing

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