Statistical Properties Of Dynamic Speckles Research Articles

Statistical properties of dynamic speckles in application to laser focusing systems.

Dynamic speckles, which carry information about beam parameters of a diffuse object, are produced by a moving diffuse object under illumination of a Gaussian beam. In this paper, we consider that the diffuse object moves in a plane with constant velocity and discuss the statistical properties of dynamic speckles for estimating the variation of focusing spot size. The space-time statistical properties of dynamic speckle have been revealed by analyzing the space-time cross-correlation function of speckle intensity fluctuations detected at two points in the receiving plane. We discuss the influence of the distance between two point detectors on the detection results by simulation analyses, and the theoretical analysis results are verified by experiment. This method, which applies feedback of the dynamic speckle fields for estimating the variation of focusing spot size, will help a laser focusing system optimize focusing performance.

The effect of speckles noise on the Laser Doppler Vibrometry for remote speech detection

Speckles noise generated by the relative in-plane motion between the Laser Doppler Vibrometry (LDV) and the target damages the quality of the LDV-captured speech severely. As such, it is necessary to research on the effect of speckles noise on the LDV for remote voice detection and remove it. In this paper, we comprehensively discuss the statistical properties of dynamic speckles with the combination of theories and experiments, and the results show that the fluctuation of speckles intensity depends strongly on the relative velocity for a given value of the detection distance. Then, we investigate the effects of the speckles noise on the LDV for remote audio detection, and the results indicate that speckles noise can cause spikes and bursts appearing in the LDV-captured voice signals, which degrades the quality of the speech. To address this issue, an algorithm of the speckle noise reduction in the LDV-measured audio signals is proposed and the experimental results demonstrate that the proposed algorithm performs well.

Statistical properties of dynamic speckles from flowing Brownian scatterers in the vicinity of the image plane in optical coherence tomography.

A closed-form analytical expression is obtained for the spatio-temporal correlation function of the scattered radiation detected in fiber-based optical coherence tomography (OCT), assuming a clean optical system arrangement in the OCT sample arm. It is shown that the transverse flow component causes purely translational speckle motion with the predicted speckle velocity 2x higher than the velocity of the flowing particles as would be observed in the image plane under incoherent illumination. It is also shown that both speckle velocity and speckle radius do not depend on the position of the scattering volume relative to the focal plane, hence the derived correlation function is independent of the position of the scattering volume relative to the focal plane. Although the analytical results are obtained for a clean optical system arrangement, they can be used with high accuracy in most practical implementations of fiber based OCT. Validation experiments in control scattering phantoms with varying liquid viscosities show excellent agreement with the developed theoretical model, under both no-flow and flow conditions. Accurate viscosity determinations enabled by this methodology may have applications to non-invasive glucose measurements in medicine.

旋转粗糙目标动态散斑统计特性研究

旋转粗糙目标动态散斑统计特性研究

Non-destructive speckle imaging of subsurface detail in paper-based cultural materials

We have used Laser Speckle Contrast Imaging (LSCI) to investigate the statistical properties of dynamic speckle reflected from an obscuring scattering surface in order to reveal drawings that are hidden beneath. Here we explore the limitations of this method used with various algorithms when applied to a selection of paper samples. These samples consist of a sketch executed in an assortment of media laid on a base surface that are then hidden beneath a subsequent top layer. The ability to resolve gray scale images was examined as well as the contrast surface temperature relationship. A book with glued pages was investigated in order to demonstrate the technique's applicability to the non-destructive examination of cultural materials. While being shown as a useful tool in revealing obscured drawings the scattering properties of the surface layer present a limitation in its general applicability.

Statistics of dynamic speckles in application to distance measurements

We present an analysis of statistical properties of dynamic speckles to estimate the limiting accuracy of measurements achievable in a distance sensor using spatially filtered dynamic speckles. The main reason for inaccurate measurements using dynamic speckles is their stochastic nature. It is shown that the average lifetime of dynamic speckles is the key factor defining the measurement accuracy. Main conclusions of the theoretical analysis were confirmed in an experiment carried out with a fast moving rough surface. Special attention is paid to a recently proposed range sensor using dynamic speckles generated by a fast-deflecting laser beam. It is shown that this sensor possesses the best combination of accuracy and response time.

Statistical properties of dynamic speckles formed by a deflecting laser beam

We analyze statistical properties of dynamic speckles formed when an optically rough surface is illuminated by a fast-deflecting laser beam. The modified space-time correlation function of the light-intensity fluctuations has been introduced to estimate the correlation parameters of a dynamic speckle pattern. Dynamic speckles are considered in their application to range sensing using evaluation of the light-power-modulation frequency of a signal obtained from the integrating photodetector after spatial filtering of the scattered light. Multichannel configuration is suggested to improve the system accuracy. Conditions that should be fulfilled to get uncorrelated responses of photodiode are found. Proper averaging of the multichannel data allows designing a non-interferometric range sensor capable for measuring distance with accuracy of 1 microm during as short time as 1 ms.

Functional imaging in photorefractive tissue speckle holography

Cellular motion produces highly dynamic speckle in wide-field depth-gated holographic optical coherence imaging. The speckle provides cell scale information such as cell membrane and organelle motion, even though the spatial resolution of the optics is above the cell scale. The statistical properties of dynamic speckle can be used for functional imaging of motile activity at depth within tissue. In this paper we develop a motility metric using time autocorrelation to create a three-dimensional motility map of tissue. The effect of noise and the shimmering showerglass effect in functional optical coherence imaging are evaluated quantitatively, and we demonstrate that meaningful motility information can be extracted from functional imaging using dynamic speckle.

Statistical properties of dynamic speckles produced by a curved surface

The statistics of dynamic speckles produced in the Fresnel diffraction field from a rotating spheroidal object under illumination of a gaussian beam are investigated. Translation and boiling motions are investigated. From the comparison between the time correlation length and the spatial translation distance of dynamic speckles, the optical condition and the curvature radius of the object are discussed and the diagram of translation and boiling motions showing their relations is shown. The cross-correlation function of dynamic speckles from the rotating spheroidal object is evaluated, and the effect of the curvature radius of the object on it is discussed.

Statistical properties of dynamic speckles

The statistical properties of dynamic speckles produced by a moving diffuse object were reviewed by providing the space–time correlation function and the power spectrum of speckle-intensity fluctuation for five combined cases of both the optical configuration and the illumination light. In the optical configuration, three kinds of geometry (free-space, single-lens, and double-lens) were taken, and three kinds of illumination light (a Gaussian beam, a plane-wave beam, and a Gaussian Schell-model beam) were used. Consequently, it was shown that the cross-correlation function and the power spectrum are both Gaussian under some assumptions. From the dynamic properties, two types of speckle motion, boiling and translation, were also evaluated for various conditions of object motion, optical configuration, and illumination light.

Dynamic laser speckles and their application to velocity measurements of the diffuse object

In connection with the parameters of the optical configuration used to produce speckles and under illumination of a Gaussian beam over a moving diffuse object, this paper discusses the statistical properties of dynamic speckles produced in the diffraction and image fields by the diffuse object moving in a plane with constant velocity. Especially, the space-time correlation function of the dynamic speckle intensity is examined in detail. Two typical speckle motions of translation and boiling are interpreted for various optical configurations in the diffraction and image fields. As one of the interesting applications of dynamic speckles to metrology, various methods for velocity measurements of the diffuse object are introduced.