The Study Of The Speckles In The Extremely Deep Fresnel Diffraction Region

In the case of Kirchhoff approximation the intensity after immediately therandom phase screen is a constant. We call the region from the output plane of therandom surface to the deep Fresnel diffraction region the extremely deep Fresnelregion. Because the speckles in extremely deep Fresnel diffraction region behavea lot of information about the scattering surface, the formation and the statisticalproperties of the speckles in this region is a long-standing problem in the study ofthe speckles. However, this problem is yet unresolved since the mathematicprocessing is complex. In this paper we study this problem by using of Kirchhoffdiffraction theory. The whole paper is divided into five chapters as the following.In chapter 1, we give a review of the description of the random surfaces, thefundamental theories of light scattering, the properties of random light fields andthe description of speckles.In chapter 2, we simulate the speckles in extremely deep Fresnel diffractionregion produced by the random surfaces which is Gaussian correlation, and studyin detail the formation and the statistical properties evolving with the distancefrom the random surface. The results show the transition from the geometricoptics effect into the interference and the diffraction effect when the distance fromthe scattering surface increases. Just because of this variation, the statistical ruleof the speckles in this region evolves from non-Gaussian into Gaussian speckleswith the propagation distance increasing. The numerical calculations of thestatistical properties of the speckles prove adequately the theory model of thetransition from the geometric optics effect into the interference and diffractioneffect in the speckles formation of this region reasonable.In chapter3, we study the speckles produced by the random surface with thepoint light source illumination, and present the mathematic expression of thespeckle intensities. Then we analyze the influence of the movement of the pointlight source on the speckle fields in extremely deep Fresnel diffraction region, andobtain the displacement rule of speckles when the point light source moves alongthe direction parallel to the random surface. We analyze the incoherentsuperposition of the speckle fields of the several point light sources, and draw aconclusion that the convolution effect appears when the extended light sourceilluminates the random surface.In chapter 4, we concentrate on the study of the partially coherent speckles.Firstly, we simulate the partially coherent speckles in extremely deep Fresneldiffraction region produced by the random surface with the extended light sourceillumination. Next, we statistically calculate the speckles contrast, and discuss indetail the influence of the width of light source, the parameters of scatteringsurfaces and the scattering distance on the statistical properties of the speckles,such as speckles contrast, the speckles probability density and the specklesintensity correlation. At last, we compare the intensity properties of the partiallycoherent speckles with that of coherent speckles, and find the phenomenon thatthe partially coherent speckles at a certain propagation distance equal to thecoherent speckles when the size of the light source is small enough. In general, thepartially coherent speckles under the practical extended light source illuminationexist only in the range involving several millimeters after the scattering surface.In chapter 5, we give a summary of this paper, and put forward the followingwork plan about the study on the speckles in the extremely deep Fresneldiffraction region.