Comparison of reconstruction-algorithm performance for optical-phase tomography of a heated air flow

An existing high-speed optical tomography system built at the Air Force Res earch Laboratory uses Hartmann wavefront sensors to obtain the optical path projections necessary for two-dimensional tomographic reconstruction of th e temperature (or equivalently the index of refraction) in a heated jet of air. Conventional optical tomography algorithms require optical-path-length projection data obtained at a number of angles through the flow. However, Hartmann sensors detect the first derivative of the path length. Convention al reconstruction algorithms thus require integration of the measured gradi ents. New iterative algorithms can reconstruct directly from the measured g radients. Using computer simulation, we compare the accuracy of reconstruct ions made directly from optical-path-length gradients with the accuracy of reconstructions based on the optical path length obtained by integrating gr adient measurements for several iterative tomographic algorithms employing local and global basis functions. For a data-limited tomography system, our studies have shown that accuracy of reconstructions depends on both the ch oice of algorithm and the structure of the flow under observation. (C) 2000 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(00)01603-2 ].