Franco-Mexican Differential Speckle Interferometer

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Abstract
Differential speckle interferometry is based on the cross analysis of series of speckle patterns produced in different wavelengths. The study of the position differences between these speckles provides angular information on objects much smaller than the diffraction limit. In order to make the measurements of the photocenter displacement, we have built an instrument which behaves like a spectrograph in one direction and a speckle interferometer in the perpendicular direction. A mirror anamorphoser permits us to meet the different sampling requirements. The dispersed speckle pattern is recorded by a photon counting camera. The measurements of the photocenter displacements are very sensitive to differences of aberration between spectral channels and temporal variations of the detector's distorsion. Our instrument provides images with a quality equal to the diffraction limit plus residual aberrations of the order of one hundreth of the wavelength used. The distorsion of the optics is much smaller than the size of the temporal variations of the detector's distorsion. In order to correct this variable distorsion, spatial and spectral modulations are made in a fully automated instrument.

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