Digital holography as a versatile optical diagnostic method for microgravity experiments

Microgravity experiments require robust, reliable and simple measurement techniques that provide the same capabilities as on-ground laboratory applications. Interferometric measurement techniques such as conventional holographic interferometry using hologram plates have several disadvantages in microgravity research-a time-consuming development process and additional experimental effort for a quantitative evaluation of interference patterns, for example. Digital holography is an advanced optical diagnostic tool for surface deformation analysis, measurement of refractive index variations and particle analysis in transparent media: Fresnel holograms are stored electronically and the reconstruction is performed by numerical methods. Due to the reconstruction process a numerical representation of the recorded wavefront can be evaluated including amplitude and phase. This paper reports on applications of digital holography to particle analysis and to the detection of refractive index variations within transparent media. The properties and advantages of this technique for microgravity experiments with respect to other techniques are discussed.