Effect of modal atmospheric compensation on angular anisoplanatism in optical interferometric imaging

Document Type

Conference Proceeding

Publication Date

12-1-1998

Abstract

Turbulence-induced phase aberrations cause the fringe pattern observed in an optical interferometer to change randomly. For long exposure measurements, the aperture-averaged mean-square differential phase between apertures comprising the interferometer baseline attenuates fringe visibility measurements, and thus reduces the ability to recover spatial-frequency spectrum information for the object being imaged. Application of modal atmospheric phase correction in each aperture of the interferometer reduces the degradation of visibility measurements when the turbulence-induced phase is measured with a wave front sensing device. For objects of interest in optical interferometric imaging, light levels are insufficient for adequate wave front sensing. Thus, a nearby naturally-occurring source must be used for modal compensation. Since this beacon is separated from the object being imaged, angular anisoplanatic effects are introduced which limit the benefits gained by the turbulence compensation. In this work, we quantify the interaperture correlation of modal aberrations, including finite outer scale and angular anisoplanatic effects. These quantities determine the residual phase upon correction of each aberration mode. For given levels of modal correction and relative aperture diameter D/ro, we establish the maximum angular separation between the beacon and the object being imaged that corresponds to an aperture-averaged mean-square residual differential phase less than 1 rad2. For D/ro = 5, we show this limit to be approximately 3 times the isoplanatic angle, θo. For D/ro = 30, however, the beacon offset is limited to approximately 0.2 θo. ©2003 Copyright SPIE - The International Society for Optical Engineering.

Publication Title

Proceedings of SPIE - The International Society for Optical Engineering

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