| Because of the advantage, such as simple-structure and noncontact and lossless andreal-time and so on, laser speckle measurement has been the research and applicationinterest. The message of the scatter in the speckle is important to detect and recognizeand analysis the micro-motion of the object. In the paper, with the theory of the laserscattering from rough objects, the second and the fourth order statistical properties ofthe scattered light have been studied, then the temporal and spatial statistical propertiesof the laser speckle which is applied to analyze the micro-motion of the object. Themain achievements are as followings:1. From the scattering theory of rough surface, the expression of the two-frequencymutual coherence function from three-dimensional convex objects with rough surfaceobeying Gaussian distribution has been derived, and the influences of the shape and thesize as well as the surface roughness of the objects on the function and the coherencebandwidth have been discussed which will be for the recognization of the objects withmore complex shape.2. Based on the Beckmann theory and Gaussian moment theorem, the expression ofthe fourth-order moment of the scattering from rough surfaces has been given which canbe expressed by two kinds of the second-order moment and the first-order moment ofthe scattered field. The influences of the incident and observation conditions and thecharacteristic parameters on the two-frequency correlation function and the angularcorrelation function of the fourth-order moment have been mainly discussed.3. With scalar Helmholtz integral relation, the distribution on the observe plane inthe far field perpendicular to the scattering direction of the speckle filed formed in freespace from rough objects with three dimension and its intensity spatial correlationfunction have been derived, the expressions of the lateral sizes of the speckles fromrough surface with different apertures and balls and cylinders and cones have beenobtained, which is closely dependent on the shape and the size of the object and thelaser wavelength as well as the distance.4. The temporal statistical properties of the dynamical laser speckle from in-planemoving rough surfaces and rotating rough objects have been investigated by thespatial-time correlation function of the speckle intensity fluctuation, and the expressionsfor the temporal correlation length of the speckle and the Doppler broadening due to therotating of the obeject have been obtained, and the relationships of them with themoving velocity and the shape as well as the size of the studied objects have been discussed respectively.5.The expression of the Doppler frequency shift caused by the in-plane movingrough objects has been derived with which the Doppler frequency shift due to therotation of the objects with rotational symetry is obtained to show that the Doppler shiftis proportional to the rotating velocity and the situation of the surface elementilluminated and the sine of the sight-in-line angle, inversely proportional to the incidentwavelength, however, independent to the roughness of the objects.6．The experiment plat form has been built to obtain the time-sequential dynamicalspeckle images of rotating rough cylinders and cones with different sight-in-line angleand different rotating velocity, which have been analyzed statistically. The results agreewell to the theoretical simulated results. With the particle group algorithm and thetheoretical derivation on the dynamic speckles, the experimental results for the timecorrelation length of the speckle have been applied to reverse the sight-in-line angle andthe rotating velocity to detect the micro-motion of the object. |
PDF Full Text Request