Speckle imaging

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

Method of large deformation measurement using speckle interferometry

Abstract: A method of deformation measurement using speckle interferometry comprises the steps of forming a series of speckle images at specified time intervals by using an interferometer to superpose a laser beam reflected from the object whose deformation is to be measured and a laser beam not affected by the object, storing the speckle images in a memory as they are formed, using the difference between the speckle image stored before the deformation and a second speckle image stored in the course of the deformation to measure the deformation between the times that the two speckle images were recorded, repeating this process for successive pairs of speckle images up to the one recorded after completion of the deformation, and adding together the individual deformation measurements obtained.

Characterization of laboratory-generated turbulence by optical phase measurements

Abstract: The resolution achieved by an optical imaging system in the presence of the random effects of the atmosphere is severely degraded from the theoretical diffraction limit. Techniques exist for recovering near diffraction-limited performance of an imaging system in the presence of atmospheric turbulence. These image enhancement techniques include speckle imaging, deconvolution, and adaptive optics. A turbulence chamber has been designed and built for laboratory testing of current and future adaptive optics and image enhancement techniques. The turbulence is produced within a chamber consisting of two small fans and a heating element. The effects of the generated turbulence on optical propagation are directly measured by sensing the perturbed wavefront phase. The wavefront phases are measured using a shearing interferometer. The statistical properties of the turbulence are then characterized by means of estimating the phase structure function from the wavefront phase measurements. We found that the estimate of the phase structure function depends only on the magnitude of the separation between two points on the optical wavefront and follows the Kolmogorov 5/3 power law.

Application of Fourier Analysis to the Laser Based Interferometric Strain/Displacement Gage

Abstract: The laser based interferometric Strain/Displacement Gage (ISDG) measures the in-plane surface deformation between two small reflecting surface markers. When illuminated with a coherent beam of light, the reflected beams from the two markers form an interference pattern, and monitoring the shift of the fringe pattern allows strain in the gage section of a specimen to be directly measured. A minimum on the fringe pattern can be isolated and tracked as the test proceeds, but this technique utilizes only a small part of the optical signal and often requires a complex programming scheme. This paper presents the application of Fourier transform and phase shifting techniques to the use of the ISDG during microsample tensile testing. The Fourier transform samples the entire fringe pattern and greatly improves the optical signal to noise ratio, and the phase shifting fringe pattern analysis has proven to be more robust and less affected by speckle or optical noise than fringe pattern minimum tracking. This results in the ability to measure larger deformations with a system resolution of ∼5 microstrain and an uncertainty of ±15.5 microstrain. An example involving the microsample tensile testing of a MEMS related LIGA Ni specimen is included to demonstrate the utility of these new techniques.

Ba II 4554 A speckle imaging as solar Doppler diagnostic

Abstract: We present observations testing the Dopplergram capability of a narrow-band (80 m A) Lyot lter imag- ing the solar surface in the wings of the Ba II 4554 A resonance line in combination with speckle reconstruction to obtain high angular resolution. The Ba II line is found to be an excellent tool for high-resolution Doppler map- ping thanks to opacity insensitivity to temperature variations and line-width insensitivity to thermal broadening. The resulting Dopplergrams show concentrated downflows of 1.2{2.2 km s 1 in intergranular lanes that probably mark magnetic fluxtubes. Two-wavelength prole sampling is found to suce for high-resolution Dopplergram construction. The lter will be installed as part of a multi-wavelength speckle imaging system on the new Dutch Open Telescope.

Data Recording And Processing For Speckle Image Reconstruction

Abstract: Image reconstruction from astronomical speckle data using the Knox-Thompson algorithm has now been extensively demonstrated as feasible through analysis and computer simulations. Experimental verification of the technique and its implementation for astronomy places stringent constraints on the recording system and requires complex processing algorithms to handle the many experimental details. In this paper we describe a video recording system specifically designed for the requirements of speckle imaging. This system has been built and tested, yielding high quality image reconstructions from a laboratory-atmospheric simulator for a wide range of input light levels and test objects.