Optimization of spatial phase shifting in endoscopic electronic speckle pattern interferometry

Endoscopic electronic speckle pattern interferometry (endoscopic ESPI) is a versatile tool for the inspection of technical and biological cavities. By the utilization of spatial phase shifting (SPS) methods, it is possible to obtain quantitative information about movements and displacements. An important quality parameter for such phase measurement techniques is a minimized noise of the phase difference. In this paper, a geometry for digital Fourier holographic reconstruction of the exit aperture of the endoscope imaging system is presented to adjust precisely and reliably the phase gradient between object wave and reference wave. Thus, the noise of the phase difference measured by endoscope SPS ESPI systems is reduced. Furthermore, the experimental setup can be simply integrated into an endoscope ESPI system with the advantage that no additional aperture in the optical path is needed.