Speckle imaging

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

Holographic and Speckle Interferometry

Abstract: This chapter explores the techniques based on holography and laser speckle. These techniques can be used to make interferometric measurements on objects with rough surfaces. The chapter describes holographic interferometry, which is a very powerful method for mapping changes in the shape of three-dimensional objects with very high accuracy. It is used widely for nondestructive testing and strain analysis. It is also very useful for the analysis of vibrations. Holographic and speckle interferometry permit measurements on objects with rough surfaces. The chapter also presents a brief introduction to holographic strain analysis and holographic vibration analysis. The simplest and most commonly used method for studying vibrating objects is time-average holographic interferometry. Speckle interferometry is explained in detail, in which the speckled image of an object is made to interfere with a reference field. The chapter also presents studies of vibrating objects. If the object vibrates, the speckle in the vibrating areas is averaged while the nodes stand out as regions of high-contrast speckle.

Laser speckle imaging with an active noise reduction scheme

Abstract: We present an optical scheme to actively suppress statistical noise in Laser Speckle Imaging (LSI). This is achieved by illuminating the object surface through a diffuser. Slow rotation of the diffuser leads to statistically independent surface speckles on time scales that can be selected by the rotation speed. Active suppression of statistical noise is achieved by accumulating data over time. We present experimental data on speckle contrast and noise for a dynamically homogenous and a heterogeneous object made from Teflon. We show experimentally that for our scheme spatial and temporal averaging provide the same statistical weight to reduce the noise in LSI: The standard deviation of the speckle contrast value scales with the effective number N of independent speckle as 1/ radicalN.

Second-order oriented partial-differential equations for denoising in electronic-speckle-pattern interferometry fringes

Abstract: We derive the second-order oriented partial-differential equations (PDEs) for denoising in electronic-speckle-pattern interferometry fringe patterns from two points of view. The first is based on variational methods, and the second is based on controlling diffusion direction. Our oriented PDE models make the diffusion along only the fringe orientation. The main advantage of our filtering method, based on oriented PDE models, is that it is very easy to implement compared with the published filtering methods along the fringe orientation. We demonstrate the performance of our oriented PDE models via application to two computer-simulated and experimentally obtained speckle fringes and compare with related PDE models.

Measurement of surface roughness properties by using image speckle contrast

Abstract: As a practical monitoring tool for measurements of surface roughness properties, a new instrument is actually constructed on the basis of using the average contrast of image speckle patterns. With this instrument an experimental investigation on the contrast variation of image speckle patterns is conducted systematically for various surface roughnesses of the objects under different conditions of an optical imaging system. It is found that the roughness and correlation length of the objects can be precisely determined from the experimental curve of the contrast variation versus the point spread of the imaging system. The present method using image speckle patterns is superior to the previous one which uses the contrast variation of speckle patterns in the diffraction field.

Spatiotemporal laser speckle contrast analysis for blood flow imaging with maximized speckle contrast.

Abstract: Laser speckle contrast imaging is a technique used for imaging blood flow without scanning. Though several studies have attempted to combine spatial and temporal statistics of laser speckle images for reducing image noise as well as preserving acceptable spatiotemporal resolution, the statistical accuracy of these spatiotemporal methods has not been thoroughly compared. Through numerical simulation and animal experiments, this study investigates the changes in the mean speckle contrast values and the relative noise of the speckle contrast images computed by these methods with various numbers of frames and spatial windows. The simulation results show that the maximum relative error of the mean speckle contrast computed by the spatiotemporal laser speckle contrast analysis (STLASCA) method, in which the speckle contrast images are computed by analyzing the 3-D spatiotemporal speckle image cube, is approximately 5%, while it is higher than 13% for other methods. Changes in the mean speckle contrast values and the relative noise computed by these methods for animal experiment data are consistent with the simulation results. Our results demonstrate that STLASCA achieves more accurate speckle contrast, and suggest that STLASCA most effectively utilizes the number of pixels, thus achieving maximized speckle contrast, and thereby maximizing the variation of the laser speckle contrast image.