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

• Published in: Optical Engineering 1995-05, Vol.34 (5), p.1374-1384
• Main Authors: Roggemann, Michael C, Welsh, Byron M, Gardner, Patrick J, Johnson, Robert L, Pedersen, Byron L
• Format: Article
• Language: English
• Subjects: Exact sciences and technology; Fluid dynamics; Fundamental areas of phenomenology (including applications); Imaging detectors and sensors; Instrumentation for fluid dynamics; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Optical elements, devices, and systems; Optical instruments, equipment and techniques; Optics; Physics; Refractometers and reflectometers
• ISSN: 0091-3286; 1560-2303
• DOI: 10.1117/12.199870

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 3D 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 and tomographic signal reconstruction. Use of wavefront sensor measurements offers higher-speed 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 effect of a limited number of projections and wavefront subaperture size. Theory, simulation, and experimental results are presented.