| Laser speckle photography and laser interferometry are both experimental techniques to nonintrusively measure the change in index of refraction of thermal flows. Both techniques share the same principles of light refraction through optically inhomogeneous media, and both record line-of-sight or path-integrated information about the flow field. For experimental conditions where the density of the flow field varies continuously along the optical path, the properties of the cross-sectional flow field must be deconvolved from the path-integrated data sets from multiple projections. This is accomplished by a mathematical technique called tomography. The present work will outline the underlying principles of optical tomography and show how it applies to the diagnostic techniques of laser speckle photography and interferometry. The two methods will be compared in various axisymmetric thermal flows. Further, it will be shown that the speckle photography technique demonstrates good potential as a new nonintrusive temperature measurement tool for various optically refractive flows. |
