Holographic diagnostics of fluid experiments onboard the International Space Station

This paper describes the holographic measurement system planned for accommo dation in the ESA Fluid Science Laboratory (FSL), a new Facility under deve lopment for the Columbus Orbital Facility of the International Space Statio n. The FSL provides research opportunities for experiments with fluids and transparent media under microgravity conditions. One of the diagnostic tool s for experimental analysis is a holographic interferometer. Holography is a method used to record and reconstruct wavefronts. The metho d has a broad spectrum of applications in the field of fluid physics resear ch on Earth and in a microgravity environment. The size, location and veloc ity of (tracer) particles inside a fluid volume can be analysed by holograp hy. and refractive index fields and corresponding temperature or concentrat ion profiles can be investigated by holographic interferometry. A number of different techniques/materials are available for hologram recording and re construction, e.g. photographic emulsions, thermoplastic films, photorefrac tive crystals and, recently, direct hologram recording with CCD sensors and numerical reconstruction (digital holography). This paper provides a surve y of these methods, defines selection criteria for the FSL and describes th e principal geometry of the FSL holographic set-up under development.