SENSING 3-DIMENSIONAL INDEX-OF-REFRACTION VARIATIONS BY MEANS OF OPTICAL WAVE-FRONT SENSOR MEASUREMENTS AND TOMOGRAPHIC RECONSTRUCTION

Light waves propagating through a region of inhomogeneous index of ref raction are aberrated. Turbulent air flows cause such inhomogeneities to arise from density fluctuations within the flow, which affect the i ndex of refraction of air. Here we describe a technique for measuring the 3-D structure of the index-of-refraction distribution in a turbule nt air flow using optical wavefront sensor measurements and tomographi c signal reconstruction. Use of wavefront sensor measurements offers h igher-speed measurement than previously used holographic methods, whil e providing high-fidelity reconstructions. We discuss Hartmann sensor measurements and wavefront reconstruction. Sampling requirements are a lso addressed, including the effects of a limited number of projection s and wavefront subaperture size. Theory, simulation, and experimental results are presented.