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For Digital Speckle Interferometry, the Fast Fourier analysis usually applied to interference fringe systems suffers from a limited spatial resolution because of the inherent granulation disturbance. Contrary, phase stepped interferometry is less influenced by speckle noise, but needs at least three phase-shifted frames at reference and object condition, or one frame with accordingly reduced resolution. For instationary objects, like an arc discharge, the phase stepping method is problematic since the phase- shifted interferograms are produced in an interferometrically unstable environment. Investigations of arc discharges showed that this problem can be solved by recording only one speckled object wavefront and referencing it with phase-stepped reference wavefronts. After low-pass- filtering, the resulting secondary speckle interferograms are treated with the common phase stepping algorithms. This technique was tested by a measurement of a deformation and was also applied to an end-on investigation of the `mini- arc', an argon arc discharge used for a secondary spectral reference.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. |
