The phase structure function has been used as a convenient way to characterize aberrations introduced on optical propagation by the atmosphere. It forms the theoretical basis for the calculation of such things as the long- and short-exposure atmospheric transfer function. The structure function is difficult to measure directly and is usually assumed to follow Kolmogorov statistics. We present here a technique for direct measurement of the structure function through the use of a Shack-Hartmann wave-front sensor. Experiments confirm that the atmosphere behaves according to Kolmogorov theory most of the time. However, some instances of non-Kolmogorov behavior have been noted.

We describe a postdetection turbulence compensation technique for obtaining high resolution imagery through the atmosphere. We present preliminary results fromfield experiments.

We report what are to our knowledge the first coherent images recovered in the laboratory from measurements made with a Shack-Hartmann wave-front sensor of the phase and amplitude of a laser speckle wave front. We discuss the design of our wave-front sensor, which can obtain the phase and amplitude of an optical field with a single intensity measurement, and we point out a particular type of phase jump that cannot be detected by the Shack-Hartmann sensor. We also discuss implementations of this technique that may permit near-diffraction-limited imaging through turbulent media.

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Since the average brightness distribution of astronomical objects and the mutual intensity (complex coherence function) of the observed field are related by a Fourier transform, it is possible to synthesize images from far-field correlation measurements. Owing to the fact that detected intensities (rather than complex fields) are correlated at the receiver, intensity interferometry is an approach to measuring such correlations, which is largely insensitive to the effects of the earth’s atmosphere. We investigate the effect that atmosphere-induced fluctuations in the detected field amplitude (i.e., atmospheric scintillation) have on one’s ability to recover imagery using intensity interferometer data. To model the effects of the atmosphere on two-point intensity correlation measurements, we have adopted the theory of Beran and Whitman1 which provides expressions for the scintillation covariance function (in the case of isoplanaticity) and a first-order isoplanatic correction. We report on our attempt to verify these relations in a laboratory setting using Gaussian phase screens of known statistics2 and an image recovery methodology known as imaging correlography.3 We also investigate the performance of postdetection processing schemes applied to compensate for the effects of scintillation in the digitally recovered imagery.