Speckle imaging

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

Single-pixel imaging using compressed sensing and wavelength-dependent scattering.

Abstract: We demonstrate two-dimensional imaging using illumination via a single-mode fiber with a multiply scattering tip and compressed sensing acquisition. We illuminate objects with randomly structured, but deterministic, speckle patterns produced by a coherent light source propagating through a TiO2-coated fiber tip. The coating thickness is optimized to produce speckle patterns that are highly sensitive to laser wavelength, yet repeatable. Images of the object are reconstructed from the characterized wavelength dependence of the speckle patterns and the wavelength dependence of the total light collected from the object using a single photodetector. Our imaging device is mechanically scan-free and insensitive to bending of the fiber, making it suitable for micro-endoscopy.

Kinematic and deformation parameter measurement by spatiotemporal analysis of an interferogram sequence

Abstract: In recent years, optical interferometry has been applied to the whole-field, noncontact measurement of vibrating or continuously deforming objects. In many cases, a high resolution measurement of kinematic (displacement, velocity, and acceleration, etc.) and deformation parameters (strain, curvature, and twist, etc.) can give useful information on the dynamic response of the objects concerned. Different signal processing algorithms are applied to two types of interferogram sequences, which were captured by a high-speed camera using different interferometric setups: (1) a speckle or fringe pattern sequence with a temporal carrier and (2) a wrapped phase map sequence. These algorithms include Fourier transform, windowed Fourier transform, wavelet transform, and even a combination of two of these techniques. We will compare these algorithms using the example of a 1D temporal evaluation of interferogram sequences and extend these algorithms to 2D and 3D processing, so that accurate kinematic and deformation parameters of moving objects can be evaluated with different types of optical interferometry.

Speckle Temporal Stability in eXtreme Adaptive Optics Coronagraphic Images

Abstract: The major noise source limiting high-contrast imaging is due to the presence of quasi-static speckles. Speckle noise originates from wavefront errors caused by various independent sources, and it evolves on different timescales pending to their nature. An understanding of quasi-static speckles originating from instrumental errors is paramount for the search of faint stellar companions. Instrumental speckles average to a fixed pattern, which can be calibrated to a certain extent, but their temporal evolution ultimately limit this possibility. This study focuses on the laboratory evidence and characterization of the quasi-static pinned speckle phenomenon. Specifically, we examine the coherent amplification of the static speckle contribution to the noise variance in the scientific image, through its interaction with quasi-static speckles. The analysis of a time series of adaptively corrected, coronagraphic images recorded in the laboratory enables the characterization of the temporal stability of the residual speckle pattern in both direct and differential coronagraphic images. We estimate that spoiled and fast-evolving quasi-static speckles present in the system at the angstrom/nanometer level are affecting the stability of the static speckle noise in the final image after the coronagraph. The temporal evolution of the quasi-static wavefront error exhibits linear power law, which can be used in first order to model quasi-static speckle evolution in high-contrast imaging instruments.

Three-dimensional deformation measurement from the combination of in-plane and out-of-plane electronic speckle pattern interferometers

Abstract: An optical setup that can be switched to produce in-plane and out-of-plane sensitivity interferometers was designed for three-dimensional deformation measuring by electronic speckle pattern interferometry. Divergent illumination is considered in the evaluation of sensitivity vectors to measure both in-plane and out-of-plane displacement components. The combination of these interferometers presents the advantage of greater sensitivity in directions u, v, and w than a typical interferometer with three illumination beams provides. The system and its basic operation are described, and results with an elastic target that is exposed to a mechanical load are reported.

Methods for parallel-detection-based ultrasound-modulated optical tomography.

Abstract: The research reported here focuses on ultrasound-modulated optical tomography based on parallel speckle detection. Four methods were investigated for signal acquisition and analysis, in which laser speckle statistics was applied. The methods were compared with the previously used four-phase method in the imaging of all-biological-tissue samples, in which the buried objects were also biological tissues. The image quality obtained with these methods was comparable with that obtained with the four-phase method; in addition, these methods have advantages in reducing acquisition time and improving the signal-to-noise ratio.