An optical tomography system, combining multi-directional holographic interferometry and computed tomography, can be a powerful tool for the study of transparent media. With such a system, one can measure the three-dimensional distribution of index of refraction in a transparent medium at an instant in time. In many situations, the index of refraction can be uniquely related to other variables of interest, for example temperature or species concentration in a gas flow. This paper reports on the development of an optical tomography system for laboratory measurements, with emphasis on the accuracy attainable with such a system. The holograph is of the diffuse-illumination type, and provides a full 90 degree angle of view of the object. Data is extracted from holograms of transparent fluids using a high-resolution CCD video camera. The digitized images are treated semi-automatically to extract fringe number versus position information. This fringe number data is then treated by a computed tomography program to reconstruct the index of refraction distribution in the fluid under study. The CT program used is an iterative technique based on Gerchberg's spectral extrapolation algorithm. The purpose of this study was to measure experimentally the accuracy of such an optical tomography system. The temperature distribution in an asymmetric convective hot air flow was measured using the optical tomography system. An array of ten fast-response thermocouples was read simultaneously with the exposure of the hologram. The thermocouple readings for several configurations are compared to the reconstructed temperatures from the optical measurement.

Date Published: 25 April 1990
PDF: 9 pages
Proc. SPIE 1162, Laser Interferometry: Quantitative Analysis of Interferograms: Third in a Series, (25 April 1990); doi: 10.1117/12.962763

Published in SPIE Proceedings Vol. 1162:
Laser Interferometry: Quantitative Analysis of Interferograms: Third in a Series
Ryszard J. Pryputniewicz, Editor(s)