Optical EngineeringCharacterization of laboratory-generated turbulence by optical phase measurements
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The resolution achieved by an optical imaging system in the presence of the random effects of the atmosphere is severely degraded from the theoretical diffraction limit. Techniques exist for recovering near diffraction-limited performance of an imaging system in the presence of atmospheric turbulence. These image enhancement techniques include speckle imaging, deconvolution, and adaptive optics. A turbulence chamber has been designed and built for laboratory testing of current and future adaptive optics and image enhancement techniques. The turbulence is produced within a chamber consisting of two small fans and a heating element. The effects of the generated turbulence on optical propagation are directly measured by sensing the perturbed wavefront phase. The wavefront phases are measured using a shearing interferometer. The statistical properties of the turbulence are then characterized by means of estimating the phase structure function from the wavefront phase measurements. We found that the estimate of the phase structure function depends only on the magnitude of the separation between two points on the optical wavefront and follows the Kolmogorov 5/3 power law.