Application of holography to fluid flow measurements using bacteriorhodopsin (bR)

This paper demonstrates the use of bacteriorhodopsin (bR) as the holographic recording medium for a holographic particle image velocimetry (HPIV) system. Using an off-axis hologram in bR, double-exposed images of particles in a turbulent flow are recorded. A high numerical aperture configuration (NA = 0.75) ensures a maximal signal intensity of the holographic recordings. Using a CCD the real particle images, that were reconstructed in the original object space, were digitized. The reconstructed image has a theoretical depth of focus of 4.73 mum and a diffraction-limited resolution of 0.43 mum. Using a priori knowledge about the flow, the flow pattern is extracted from the double-exposed particle images. A liquid crystal shutter was employed during the reconstruction in order to minimize photo-induced erasure. Details of the experimental set-up, as well as the difficulties which were encountered during this investigation, are discussed in this paper. The paper also discusses various multiplexing methods and their suitability for use with bR to remove directional ambiguity in HPIV.