Digital holography of particle fields.pdf

Digital holography of particle fields: reconstruction by use of complex amplitude Gang Pan and Hui Meng Digital holography appears to be a strong contender as the next-generation technology for holographic diagnostics of particle fields and holographic particle image velocimetry for flow field measurement. With the digital holographic approach, holograms are directly recorded by a digital camera and recon- structed numerically. This not only eliminates wet chemical processing and mechanical scanning, but also enables the use of complex amplitude information inaccessible by optical reconstruction, thereby allowing flexible reconstruction algorithms to achieve optimization of specific information. However, owing to the inherently low pixel resolution of solid-state imaging sensors, digital holography gives poor depth resolution for images, a problem that severely impairs the usefulness of digital holography espe- cially in densely populated particle fields. This paper describes a technique that significantly improves particle axial-location accuracy by exploring the reconstructed complex amplitude information, compared with other numerical reconstruction schemes that merely mimic traditional optical reconstruction. This novel method allows accurate extraction of particle locations from forward-scattering particle holograms even at high particle loadings. ? 2003 Optical Society of America OCIS codes: 120.7250, 120.3940, 090.1760, 100.3010.1. Introduction In many applications involving particle fields there is a pressing need to develop capabilities to measure instantaneous three-dimensional
3D distributions of small particles dispersed in a flow. For example, in the prediction of raindrop formation in the atmo- sphere, in the design of fine-spray combustion noz- zles, in the production of fine-scale pigments, and in the control of industrial emissions, it is important to model the dispersion, collision, and coagulation of particles suspended in turbulence. Without th