Instantaneous 3-D optical tomography for flow visualization

A new optical architecture for making instantaneous tomographic measurements of a time-varying, three-dimensional flow field is discussed. The system is capable of providing 36 views of a transparent object in 300 μsec using a 1 Watt Argon laser. The size of the measurement volume is 7 cm × 7 cm × 7 cm. Spatial resolution is estimated to be approximately 1.5 mm and the error in measurement of concentration is better than 3%. The projections are holographic-interferometry phase measurements of density. The set of projections is inverted using Fourier processing techniques to yield the three-dimensional representation of the density field. The results of these measurements are displayed using the SURF graphics package developed at Stanford. This system is used to study a coflowing helium-air jet. Instantaneous 3-D concentration measurements of helium into air in the transitional region of the jet are presented.