Speckle imaging

About: Speckle imaging is a research topic. Over the lifetime, 3730 publications have been published within this topic receiving 62354 citations.

Speckle Interferometry at the US Naval Observatory. VIII.

Abstract: The results of 2044 speckle interferometric observations of double stars, made with the 26 inch (66 cm) refractor of the US Naval Observatory, are presented. Each speckle interferometric observation of a system represents a combination of over a thousand short-exposure images. These observations are averaged into 1399 mean positions and range in separation from 016 to 1497, with a mean separation of 251. This is the eighth in a series of papers presenting measures obtained with this system and covers the period 2001 March 18 through 2001 December 30.

Wide field-of-view, high-resolution Solar observation in combination with ground layer adaptive optics and speckle imaging

Abstract: Context. High angular resolution images at a wide field of view are required for investigating Solar physics and predicting space weather. Ground-based observations are often subject to adaptive optics (AO) correction and post-facto reconstruction techniques to improve the spatial resolution. The combination of ground layer adaptive optics (GLAO) and speckle imaging is appealing with regard to a simplification of the correction and the high resolution of the reconstruction. The speckle transfer functions (STFs) used in the speckle image reconstruction mainly determine the photometric accuracy of the recovered result. The STF model proposed by Friedrich Woger and Oskar von der Luhe in the classical AO condition is generic enough to accommodate the GLAO condition if correct inputs are given. Thus, the precisely calculated inputs to the model STF are essential for the final results. The necessary input for the model STF is the correction efficiency which can be calculated simply with the assumption of one layer turbulence. The method for calculating the correction efficiency for the classical AO condition should also be improved to suit the GLAO condition. The generic average height of the turbulence layer used by Friedrich Woger and Oskar von der Luhe in the classic AO correction may lead to reduced accuracy and should be revised to improve photometric accuracy.Aims. This study is aimed at obtaining quantitative photometric reconstructed images in the GLAO condition. We propose methods for extracting the appropriate inputs for the STF model.Methods. In this paper, the telemetry data of the GLAO system was used to extract the correction efficiency and the equivalent height of the turbulence. To analyze the photometric accuracy of the method, the influence resulting from the distribution of the atmospheric turbulence profile and the extension of the guide stars are investigated by simulations. At those simulations, we computed the STF from the wavefront phases and convolved it with the high-resolution numerical simulations of the solar photosphere. We then deconvolved them with the model STF calculated from the correction efficiency and the equivalent height to obtain a reconstructed image. To compute the resulting photometric precision, we compared the intensity of the original image with the reconstructed image. We reconstructed the solar images taken by the GLAO prototype system at the New Vacuum Solar Telescope of the Yunnan Astronomical Observatory using this method and analyzed the results.Results. These simulations and ensuing analysis demonstrate that high photometric precision can be obtained for speckle amplitude reconstruction using the inputs for the model STF derived from the telemetry data of the GLAO system.

Inversion of speckle interferometer fringes for hole-drilling residual stress determinations

Abstract: Speckle interferometric fringe patterns record stress-relief displacements induced by the drilling of blind-holes into prestressed objects. The quantitative determination of residual stress state from such stress patterns is difficult because of the ambiguity in the order of the observed fringes. The plane stress magnitudes are provided directly from selected fringe positions using a stochastic, iterative least squares minimization approach. The inversion requires prior knowledge of the experimental geometry and an appropriate uniaxial stress-relief displacement basis function derived from three-dimensional finite element calculations. Superpositioning of the rotated and scaled displacement basis functions allows the stress-relief relaxation for any biaxial state of stress to be determined. In this paper, fringe patterns were forward modeled from a large ensemble of calculated biaxial stress-relief displacement fields. Inversion of these noise-free fringe patterns reproduced the biaxial stresses with negligible error. Analysis of more realistic fringe patterns that include speckle noise gave stress magnitude errors that diminished rapidly with the number of selected points to better than 3 percent for 100 points. Sensitivity of the optical method is influenced by a number of factors, but the ensemble of model fringe patterns studied indicates that the stress magnitudes (nomalized with respect to the material's Young's modulus) from 3×10−4 to 10−2 can accurately be determined with visible laser radiation. The method is amenable to automation and can easily be extended to study near surface gradients in the residual stresses or applied to other optical recording techniques such as moire and phase-shifting interferometry.

Astronomical Site Selection : A New Meteorological Approach

Abstract: In order to be efficient, new astronomical methods, like high angular resolution and speckle interferometry require subarc second seeing conditions and long speckle boiling time. It is now well known that there is a close relationship between the seeing and the integrated vertical profile of atmospheric turbulence, from the focus plane of the telescope up to the stratosphere. The measurement of the spread function of a star image does not tell anything about the respective contributions of the inside of the dome, the boundary layer and the free atmosphere. Disturbances coming from the first two slabs can be avoided by : removing the heat sources, cooling the floor, building the observatory above the inversion layer, simulating the site in a wind tunnel... But there is no a priori knowledge about the free atmosphere turbulence. In the literature, such profiles are too scarce and sparse to foresee a clima-tology. In this paper, it will be shown that there is a strong experimental correlation between a good seeing and a low wind speed at the tropopause level. The study rely on already published sesonal variations of the seeing in La Silla, Chile, and Hawaii, and on atlas of climatology of the atmospheric circulation at 200 millibars level. It seems that subarc second seeing conditions require tropopause wind speeds lower than 20ms-1. A quick look at the wind behavior let us hope very good image quality above sites located in the northern part of Chile, near Peru. A fortunate consequence of our assumption is that slow tropopause wind selected sites will likely have a long speckle time life.

Improving the axial and lateral resolution of three-dimensional fluorescence microscopy using random speckle illuminations.

Abstract: We consider a fluorescence microscope in which several three-dimensional images of a sample are recorded for different speckle illuminations. We show, on synthetic data, that by summing the positive deconvolution of each speckle image, one obtains a sample reconstruction with axial and transverse resolutions that compare favorably to that of an ideal confocal microscope.