Higher-order Coherence Effects Of Light Waves On Weak Scattering And Design Of New Types Of Scattering Media

When a light beam propagates in a medium with inhomogeneous optical properties,the light can be seen from the side,and this phenomenon is called light scattering.The physical nature of light wave scattering is the interaction between light and matter.Therefore,the statistical characteristics of the scattered field are closely related to the structural characteristics of the scattering medium.In other words,the scattered field will carry structural information of the medium,which is of great significance to the situation where the structural information of objects cannot be directly detected in practice.Therefore,the statistical properties of the scattered field attracted substantial attention of researchers.In the past,the research on the scattered field mainly focused on its second-order statistical properties,such as spectral density,spectral degree of coherence,spectral degree of polarization and so on,and we still know very little about the higher-order coherence effects of the scattered field.Moreover,the higher-order coherence effects of the scattered field contain more structure information of the scattering medium,which is particularly important for accurate reconstruction of the scattering medium,such as biomedical diagnosis.On the other hand,with the rapid development of manufacturing technology and 3D printing technology,manufacturing products with a spatial resolution on the order of several microns has become a reality.This provides a solid experimental basis for designing a scattering medium with a specific correlation structure to realize the manipulation of the scattering field.In the past 10 years,researchers have successively proposed models of the scattering medium that can produce specific scattered intensity distributions,and realized the scattering fields with flat-top,frame-like,ring-like,square and rectangle structures.In the context of the above research,this dissertation discusses light waves on weak scattering within the accuracy of the first-order Born approximation and the far-field approximation.Firstly,we study the far-field behaviors of light waves on scattering from a collection of hybrid particles.Subsequently,the higher-order coherence effects of the scattered field are studied in detail,which mainly includes two aspects:correlation between intensity fluctuations of polychromatic electromagnetic light waves on weak scattering and condition for the maintenance of the coherence of a fully coherent light wave on weak scattering.Finally,the problem of designing new types of scattering media is studied,and a new type of scattering medium that can produce an array distribution in the far-zone scattered field is proposed,and a new method of designing a scattering medium based on the convolution theory is proposed.The chapters of the dissertation are arranged as follows:Chapter 1 introduces the research history and development trend of light scattering.Then,the basic knowledge involved in this dissertation is introduced,which mainly includes three aspects:the weak scattering theory of scalar light waves,the weak scattering theory of vector light waves,and the description of the quasi-homogeneous medium as well as a collection of particles.Chapter 2 proposes a particulate medium model with a mixture of deterministic and random particles,and derives the general analytical expressions for the spectral density and spectral degree of coherence of the far-zone scattered field.The influence of the location of the deterministic particles and the distribution of the random particles on the far-zone spectral density and spectral degree of coherence is discussed in detail.Chapter 3 studies the correlation between intensity fluctuations of polychromatic electromagnetic light waves on weak scattering.Firstly,a general theory of correlation between intensity fluctuations of polychromatic electromagnetic light waves on weak scattering from a random medium is established-Then,taking the quasi-homogeneous medium and the light source with a Gaussian spectrum as an example,the influence of the structure parameters of the scattering medium and the frequencies of the incident light waves as well as scattering angles on the spectrum of intensity fluctuation correlations in the far-zone field is discussed in detail.Furthermore,the expression is derived for the critical angle at which the central frequency of the spectrum of intensity fluctuation correlations remains unchanged during the scattering process.Based on this critical angle and the parameter of the light source,the method to determine the structure parameters of the quasi-homogeneous medium is presented.Finally,the scaling law for correlation between intensity fluctuations of polychromatic electromagnetic light waves on weak scattering is proposed.Chapter 4 studies the condition for the maintenance of the coherence of a fully coherent light wave on weak scattering.Firstly,in the light of the perspective of statistical similarity,we give the condition for the maintenance of the second-order coherence of a fully coherent light wave on weak scattering,and the nature of the second-order coherent scattered field indicated by this condition is explained in detail.Subsequently,by assuming that the scattered field has remained the second-order coherence of the incident field,we further discuss the maintenance of higher-order coherence,and give a simple method to describe the higher-order coherence of the scattered field.It is proved that the combination of the maintenance of the second-and fourth-order of the incident field implies the scattered field coherence to all orders.Finally,we reveal the structure characteristics of the scattering medium for a coherent scattered field,in particular,in the case of the second-order coherence.Chapter 5 studies the design of new types of scattering media.Firstly,under the Markov approximation,the expression is derived for the relationship between the far-zone spectral density and the degree of potential correlation of the random medium.Based on this,a class of scattering medium model with a new type of correlation structure is designed,so that the far-zone spectral density when light waves on scattering from this kind of medium can be distributed in an array form.Then,based on the convolution theory,we further propose a new method of designing a scattering medium.The advantage of this method is that the scattered field can be manipulated more flexibly and with many degrees of freedom.Chapter 6 is the summary part,which outlines the main works and innovations of this dissertation,and puts forward the outlook for the future work.