Sensing three-dimensional index-of-refraction variations by means of optical wavefront sensor measurements and tomographic reconstruction

Light waves propagating through a region of inhomogeneous index of refraction are aberrated. Turbulent air flows cause such inhomogeneities to arise from density fluctuations within the flow, which affect the index of refraction of air. Here we describe a technique for measuring the 3-D structure of the index-of-refraction distribution in a turbulent air flow using optical wavefront sensor measurements and tomographic signal reconstruction. Use of wavefront sensor measurements offers higherspeed measurement than previously used holographic methods, while providing high-fidelity reconstructions. We discuss Hartmann sensor measurements and wavefront reconstruction. Sampling requirements are also addressed, including the effects of a limited number of projections and wavefront subaperture size. Theory, simulation, and experimental results are presented.