Holographic interferometric metrology allows a fast, non destructive and quantitative high resolution full field detection of optical path length changes. Furthermore, by utilization of modern CCD sensor technology and digital image process-ing algorithms an on-line application of these methods even on biological specimens is possible. In combination with a microscopic resolution this offers new possibilities for the detection of variations of shape, micro movements or refractive index changes e. g. for the marker free analysis of cellular samples. Three holographic interferometric systems for microscopy applications based on digital holography, (speckle) interferometry and photorefractive crystals as holographic recording medium are introduced. Results of investigations on test charts and biological samples to characterize and optimize the lateral resolution as well as the resolution of the detected phase difference changes are presented and discussed. Finally, the applicability of the developed measurement techniques on living cells is demonstrated.
Endoscopic Electronic-Speckle-Pattern Interferometry (endoscopic ESPI) is a tool for the detection and the measurement of displacements and movements in technical and biological cavities. For an adequate measurement accuracy additional to the geometry of imaging and illumination, information about the shape and curvature of the investigated cavities is required. Investigations to measure the surface topometry by endoscopic ESPI combined with a two-wavelength method have been carried out. The advantage of this arrangement, which uses commercial endoscope imaging systems, is that it is possible to obtain object shape and displacement data with the same endoscopic interferometric measurement system. Therefore, in a first step, the phase difference distribution effected by the change of the illumination wavelength and the object shape is detected by spatial phase shifting and in a second evaluation step, the radial distortions of the endoscope imaging system are corrected and the geometry of endoscopic off-axis illumination is taken into account by an approximation.
The method of endoscopic electronic-speckle-pattern interferometry (ESPI) is a tool for detection and visualization of deformations and movements in technical cavities as well as for non-destructive minimal invasive diagnostics within body cavities. Here, a spacial phase shifting (SPS) method is chosen for additional setup and the investigated specimen in comparison to temporal phase shifting techniques. With a simple arrangement, the SPS technique is adapted to the special conditions of standard endoscopic optical imaging. The characterization and optimization of the interferometer is carried out on technical specimen. To demonstrate possible applications of endoscopic ESPI and spatial phase shifting endoscopic (ESPI) on biological tissues, non-destructive investigations of biological heart valve prostheses are performed. The quality of the obtained phase difference fringes is sufficient for phase unwrapping and for visualization as well as quantitative evaluation. In conclusion, the results of the investigations show that it is possible to detect structural differences in tissues underneath the visible surface by application of SPS endoscopic ESPI even of biological specimen with a wet and low reflecting surface.
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