Reusable holographic velocimetry system based on polarization multiplexing in bacteriorhodopsin

Abstract

We present a novel holographic particle image velocimetry (HPIV) system using a reversible holographic material as the recording medium. In HPIV the three-dimensional flow field throughout a volume is detected by adding small tracer particles to a normally transparent medium. By recording the particle distribution twice with a known time shift the displacement and the velocity of the tracer particles can be retrieved. From this information the instantaneous three-dimensional flow field can be found. Our measurement system records double exposure particle holograms in a film based on the photo-chromic protein bacteriorhodopsin (BR). Polarization multiplexing is used to separate the two constituent holograms. We believe it is the first time that this type of multiplexing is used in (particle) velocimetry measurements. By using a polarization sensitive material we are able to simplify our setup and increase the storage capacity of our holographic medium. BR is a fully reversible recording material that does not require any chemical processing. This allows for fast experiments that require minimal operator involvement. A full measurement cycle can typically be completed within several minutes. We present our experimental system in detail and we will discuss how the material and optical properties of BR affect the holographic recording system. We will point out the advantages, disadvantages, and practical issues involved when working with BR.