TIME-VARYING SPECKLE PHENOMENA IN ASTRONOMICAL IMAGING AND IN LASER SCATTERING

The properties of time-varying speckle phenomena in stellar imaging through turbulence and in laser scattering from moving diffusers are examined in both theory and experiment. It is found that the space-time correlation properties of stellar speckle images are important in stellar speckle interferometry, a method of obtaining diffraction limited information through the atmosphere. A theoretical study of exposure time effects in speckle interferometry reveals that the optimum exposure time is dependent on the space-time properties of the stellar image. A method of space-time speckle interferometry that may overcome exposure time effects of standard methods is also proposed. An experimental investigation of the space-time intensity correlation functions of the speckle image at two observing sites reveals rather different correlation structure. At Mees Observatory in Bristol Springs, New York, the image correlations indicate that translation of pupil turbulence was significant, while measurements at Mauna Kea Observatory in Hawaii suggest that boiling of turbulence rather than translation was the predominant effect.; An analogous effect in laser scattering from moving diffusers is studied in some detail. In the experiment considered a translating diffuser is placed in the pupil of a lens and the time-varying speckle in the focal plane is studied. In this case the moving diffuser in front of the lens is analogous to wind-driven turbulence translating across the telescope objective. The theoretical space-time intensity correlation functions are calculated in the gaussian scattered amplitude limit and are found to be rather similar to those measured at Mees Observatory. Experimental measurements of the time-varying laser speckle are presented and excellent agreement with the theory is obtained. The detection of small amounts of aberrations and measurements of the lens modulation transfer function are possible applications of this phenomenon.; A theoretical study of the photon correlation techniques used in measuring the space-time intensity correlations is presented. It is found that a number of non-ideal effects such as photon overflows in one signal, prescaling of photon counts, detector dead-time, and dark current do not significantly alter the form of the photon correlation in the case of gaussian light, though the strength of the correlation may be affected. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI...