Statistical Properties Of Laser Speckles And Detection Micro-motion For Arbitrary Targets With Rough Surface

The laser speckle characteristics of roughness targets have been intimately noticedby national defense and aerospace fields. Laser speckle that carry information of thetarget was basis for target discrimination with laser radar,3D imaging involvingmachine vision and dimensional metrology. The main achievements are as followings:the physical process and measurement methods of laser speckle, the probability densityfunction of speckle intensity and phase, the receiving aperture’s impact on the statisticalnature of speckle field from curved face objective, The analyzing for the dynamicproperties of two types of speckle motion, boiling and translation in opticalconfiguration and illumination light, the object motion parameters based on laserspeckle. There are main research results as follows:1. The physical process of laser speckle is described in detail based on interferencetheory and summation rule of random vectors. A physical model of the instantaneousintensity at any point in scattered field, autocorrelation function and power spectraldensity of the laser speckle from a rough surface is provided separately. Probabilitydensity distribution of speckle intensity is given on receiving screen.2. In order to explore the statistical properties of integrated intensity fluctuations ofdynamic speckles produced in the Fresnel diffraction field from a rotating curvatureobject under illumination of a Gaussian beam, the dependence of the curvature radius ofthe rotating diffuse object on the correlation time of the speckle intensity fluctuation isespecially expressed by taking into account the size of the detecting aperture. Indifferent detecting aperture, the correlation distance of the speckle intensity fluctuationis calculated from plane and sphere surface, and the relation of time correlation lengthof the speckle intensity fluctuation with the radius of curvature is given when thecurvature objects are rotating with constant angular velocity. And rotationaldecorrelation feature from a cylindrical on square receiving aperture is considered.Statistical property of dynamic speckles in the Fresnel diffraction field is describedwhen irradiated area is greater than cylinder surface. The changing relationship isobtained on both numerical computation and experimental which the space.timecross.correlation of dynamic speckles intensity fluctuations as cylindrical radius androtation speed.3. The statistical properties of dynamic speckles produced by a moving diffuseobject are reviewed by a deduced space.time correlation function and power spectrumof speckle-intensity fluctuation for five combined cases of both optical configuration and illumination light. Three kinds of geometry (free-space, single-lens, and double-lens)of optical configuration are taken with three kinds of illumination light (Gaussian beam,plane-wave beam, and Gaussian Schell-model beam). Consequently, it is shown that thecross correlation function and the power spectrum are both Gaussian under someassumptions. Two types of speckle motion (boiling and translation) are also evaluatedunder different kinds of motion conditions, optical configuration and illumination lightfrom the dynamic properties.4. The expressions of space-time correlation function of speckle.intensityfluctuation are derived when the object translation three.dimensional motion, sinevibration, angular vibratory and rotate at a constant speed are considered. Correlationlength and relative temporal in the different motion states is presented by means ofsimulated calculation. Curves of speckle-intensity fluctuation are drawn with waist sizeof the incident Gaussian beam, the parameter of optical system and the motion targetspeed. The distributional features of averaged power spectrum are analyzed and theimpact of speckle translation and speckle boiling caused by rotation cylinder on thereceived signal bandwidth is concluded.5. The relationship between range resolved laser radar cross section and thefluctuating speckle intensity caused by scanning the laser frequency is describedtheoretically. The fundamental relation is established between the spectral density of thespeckle signal and the autocorrelation function of the range-resolved laser radar crosssection of illuminated object. The wavelength dependence of speckle and phaserecovery of range resolved laser radar cross section is presented using a statisticalmethod.