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Showing papers on "Speckle imaging published in 1973"


Journal ArticleDOI
TL;DR: In this paper, mathematical expressions for the Wiener spectrum of the image of a point source were obtained for angular frequencies much less than, and much greater than, the conventional seeing limit.
Abstract: A new technique (speckle interferometry) has been developed by Gezari, Labeyrie, and Stachnik, which allows the measurement of stellar diameters from a series of photographs obtained from large-aperture ground-based telescopes. The series of photographs is processed to obtain the Weiner spectrum of the photographic image, i.e., the ensemble-averaged modulus-squared Fourier transform obtained from the series of images. Gezari, Labeyrie, and Stachnik have measured stellar diameters as small as 0″.05, about 20 times better than is usually possible. In this paper, mathematical expressions are obtained for the Wiener spectrum of the image of a point source. As is well known, the Wiener spectrum of the image of an extended, incoherently radiating object, is expressible as a product of this point-source spectrum and the object spectrum. Calculations are performed using the Rytov approximation and assuming that the underlying atmospheric turbulence is describable by a Kolmogorov spectrum. Asymptotic closed-form expressions are obtained for angular frequencies much less than, and much greater than, the conventional seeing limit. In the latter case, the Wiener spectrum is found to be proportional to the optical transfer function.

234 citations


Journal ArticleDOI
TL;DR: A direct extension of this method to holographic microscopy, using a multitone laser, should permit one to record and reconstruct holograms of diffraction-limited resolution that are essentially speckle-free.
Abstract: The occurrence and smoothing of speckle are studied as a function of the line width for a highly collimated illuminating source. A general theory is presented for speckling in the image of a partially diffuse, phase type of object, which has a variable number of random scattering centers per resolution element. Then, an expression is derived for the wavelength spacing required to decouple the speckle patterns arising from two monochromatic tones in an imaging system, thereby establishing that it is feasible to smooth speckle using multicolor illumination. This theory is verified in a series of experiments using both laser illumination and band-limited light from a carbon arc. With highly collimated sources, we show that speckle appears laserlike for an imaged diffuser even up to line widths of 5 A. Then, smoothing of speckle is demonstrated in the imaging of a diffuser and for a section of an optic nerve when the illumination is provided by six narrow lines spread over 1500 A. Since with color-blind, panchromatic viewing the speckle smooths, a direct extension of this method to holographic microscopy, using a multitone laser, should permit one to record and reconstruct holograms of diffraction-limited resolution that are essentially speckle-free.

184 citations



Journal ArticleDOI
TL;DR: In this article, the technique of speckle interferometry was applied to solar photographs, and spatial frequencies as high as 4 cycles per arc second were detected in sunspots.
Abstract: The technique of speckle interferometry was applied to solar photographs. Spatial frequencies as high as 4 cycles per arc second were detected in sunspots.

33 citations


Journal ArticleDOI
TL;DR: In this article, the authors calculate the diffraction patterns corresponding to some simple object displacements basing themselves on the fact that the intensity distribution in a speckle pattern can be assumed to be equivalent to an ensemble of sinusoidal gratings of different frequencies and different orientations.
Abstract: Deformations undergone by a diffuse object can be determined by speckle interferometry. The object, illuminated in coherent light, is photographed on a high resolution emulsion. Two exposures are made, before and after the object has undergone the deformation. The doubly-exposed photographic plate produces diffraction figures that determine the object deformation. These diffraction effects have been calculated and observed by a number of authors. In this article we calculate the diffraction patterns corresponding to some simple object displacements basing ourselves on the fact that the intensity distribution in a speckle pattern can be assumed to be equivalent to an ensemble of sinusoidal gratings of different frequencies and different orientations.

5 citations


Journal ArticleDOI
TL;DR: In this paper, the authors applied incoherent-to-coherent conversion and optical information processing to harmonic analysis of random spatial structures (speckle interferometry [1] analysis of shadow patterns associated with stellar scintillation [2]).
Abstract: Several authors have recently applied incoherent-to-coherent conversion and optical information processing, to harmonic analysis of random spatial structures (speckle interferometry [1] analysis of shadow patterns associated with stellar scintillation [2]). Spatial power spectra are obtained by adding on a single photographic plate the intensity of the diffraction patterns produced by a large number of statistically independant images recorded on a photographic film. On the other hand, incoherent-to-coherent conversion has been performed using the dynamic scattering mode in nematic liquid crystals as an image storing device [6], [7], [8]. Such a device meets the needs for a real time statistical analysis of random structures. It is shown that temporal filtering (modulation) can be combined with spatial harmonic analysis in order to obtain three dimensional power spectra W(k, ω) of evolving random structures, as a function of the wave number k and of the temporal frequency ω. An experiment has been performed in which a random distribution of light dots in uniform motion is analysed. The diffraction pattern, recorded on a photographic plate with a 2s integration time, shows clearly interference fringes out of the noise(fig. 4). The separation of adjacent fringes is proportionnal to the modulation frequency and to the inverse of the speed of motion. Application such as the continuous monitoring of the velocity of a flow or the identification of atmospheric turbulent layers from the analysis of the motion of the shadow patterns associated with stellar scintillation, can be anticipated.