Holographic diagnostics of fluid experiments onboard the International Space Station

Abstract

This paper describes the holographic measurement system planned for accommodation in the ESA Fluid Science Laboratory (FSL), a new facility under development for the Columbus Orbital Facility of the International Space Station. The FSL provides research opportunities for experiments with fluids and transparent media under microgravity conditions. One of the diagnostic tools for experimental analysis is a holographic interferometer. Holography is a method used to record and reconstruct wavefronts. The method has a broad spectrum of applications in the field of fluid physics research on Earth and in a microgravity environment. The size, location and velocity of (tracer) particles inside a fluid volume can be analysed by holography, and refractive index fields and corresponding temperature or concentration profiles can be investigated by holographic interferometry. A number of different techniques/materials are available for hologram recording and reconstruction, e.g. photographic emulsions, thermoplastic films, photorefractive crystals and, recently, direct hologram recording with CCD sensors and numerical reconstruction (digital holography). This paper provides a survey of these methods, defines selection criteria for the FSL and describes the principal geometry of the FSL holographic set-up under development.