Holographic particle diagnostics

Abstract Holography is now an accepted method of interrogating particle fields and multiphase flows. Yet, holography systems are not produced in a commercially available form due to the complexity and variety of systems needed for different applications. As such, individual researchers must design and construct their own systems, systems which are usually tailored to specific applications. The process of designing and constructing a holographic system is complex and, to our knowledge, there is only one summary of the issues to be considered during this procedure. Consequently, holography is not as widely used as it might be. In addition, while several excellent reviews of holographic particle diagnostic systems have been published in the past, an updated review is overdue. Two contributions worthy of special note are “Selected Papers on Holographic Particle Diagnostics” (an SPIE publication) edited by C. Vikram, and the recent book entitled Particle Field Holography by C. Vikram. The SPIE publication is an excellent source of early papers on holographic particle diagnostics. The book is an excellent and thorough description of the foundations of holography and is highly recommended reading for anyone interested in the field. The purpose of this review article is therefore twofold. First, we hope to inform engineers and scientists of the issues to be considered and the options available to them when designing and constructing a holographic particle diagnostic system. Second, we hope to provide them with a history of previous efforts in the field so that if work has been done in an area similar to theirs they will be able to locate it and use it to facilitate their own research. Types of holographic techniques discussed in this paper include in-line, in-line Fraunhofer (far-field), and off-axis, using either diffracted or reflected light. Film types and light sources are also briefly noted. Some of the applications discussed are: spray injection systems (including rocket engine injection, aerosols, and coal injection), combustion processes, cavitation studies and internal two-phase flows, bubble chamber studies, and microbiology. Finally, a number of papers are discussed that describe innovations in the field of automated analysis of particle field holograms. This area must be pursued if holography is to become a time efficient diagnostic tool.