Interferometric Tomography

Snyder and Hsselink [33] introduced the idea of combining holographic optical elements with tomography, thus permitting high-speed, high-resolution flow visualization. In a similar work aimed at recording microsecond events at a high-speed, Zoltani et al. [34] have used a flash X-ray source. Gmitro and Gindi [35] have described an electrooptical device that can perform reconstruction with the CBP algorithm at video-rates.  The idea here is to use optical elements to carry out some of the numerical integration needed for three-dimensional reconstruction. Tomography applied to interferometric data can be seen in the work of Faris and Byer [36] for supersonic jets where refraction effects have been accounted for. Snyder [37] has Studied species concentration in a co-flowing jet using tomographic interferometry. Liu et al. [38] used photographs to initiate tomographic reconstruction and have applied the method to axisymmetric and asymmetric helium jets. Watt and Vest [39] studied structures of turbulent helium jets in air by recording the path integral images based on the refractive index variation using a pulsed phase-shifted interferometer. The advantage of this method is that one can record the phase of the light wave as continuous data, rather than discrete fringes. This greatly improves the spatial resolution of the measurement, being the pixel size rather than the fringes spacing. Subsequently, the authors have tomographically reconstructed the helium concentration field. Tomographic measurement techniques and the appropriate reconstruction algorithms suitable for the process industry have been discussed by Mews et al. Michael [40] and Yang [41] have discussed three-dimensional reconstruction of the temperature field using an iterative technique. A mach-Zehnder interferometer was used in this work on Rayleigh-Benard convection with water as the working fluid. Bahl and Liburdy [42] have discussed tomographic reconstruction for a synthetic temperature field. Soller et al. [43] applied iterative tomographic techniques to study interaction of supersonic jets and independently to buoyancy-driven convective flow around a light bulb. they have noted significant advantages in the tomographic approach, particularly when the recorded data is incomplete. Sato and Kumakura [44] developed the dual plate Fourier transform interferometry to improve the spatial resolution of the measurement by introducing a carrier frequency that modulates the usual fringe patterns. This instrument has then been used to map the thermal field in premixed flames.