The Properties And Manipulation Of Far Field Of Light Waves On Weak Scattering

The weak scattering theory of light waves,which is a theory to investigate the influence of the optical properties of the incident field and the structure characteristics of the scattering medium on the behaviors of scattered far field,has attracted extensive attention of researchers due to its widely applications in remote sensing,detection,and medical diagnosis.Since Korotkova generalized the light field control technology to the areas of weak scattering theory,great progress has been made in manipulation of far field in the process of weak scattering,and scattered far field distribution with various patterns,including circular flat distribution,rectangular distribution,array distribution and ring-shape distribution,has been obtained.In this dissertation,based on the first-order Born approximation and the Markov approximation,the properties and manipulation of light waves scattered by a medium are studied.The specific research work is as follows:1.The beam conditions of light waves scattered by a particle medium were studied.The expression of far field spectral density of light waves scattered by a particle medium was derived,and the possibility of scattered field with beam-like form generated by a particle medium was discussed.The results show that whether the scattered far field may behave as a beam-like depends on the effective width of the scattering potential of a particle collection and the effective coherence length of the particle distribution function.An example of a particle medium with quasi-homogeneous Gaussian distribution was given to illustration the beam conditions.This conclusion may have potential applications in areas such as measurement and manipulation of scattered far field.2.The equivalence theorem of light waves scattered by anisotropic medium was studied.The expression of far field spectral density of light waves scattered by anisotropic medium was derived,and the possibility of two different anisotropic media to produce far field with identical spectral density distribution was discussed.In some special cases,the scattered far field can be completely equivalent in the whole three-dimensional space or partially equivalent in some two-dimensional planes.This conclusion may be applied to the accurate measurement of scattering media.3.The method to manipulate scattered far field by convolution of weight functions was presented.A novel medium model was designed by using the convolution of weight functions,and the expression of far field spectral density of light waves scattered by this medium was derived.Two typical scattering medium models were studied in detail,including the case that the two weight functions involved in convolution are of the same type and of the different types.These novel scattering medium models can be used to generate a stable or tunable far field distribution.This research work generalize the method of designing media from linear combination to non-linear combination,which has potential significance for the manipulation of scattered far field.4.The method to obtain the scattered far field with hollow distribution by linear combination of weight functions was presented.The medium model which can produce hollow scattered far field was designed by using the linear combination of weight functions,and the expression of spectral density of far field was derived.This scattering medium can be used to generate a hollow scattered far field,and the profile of the hollow shape and of the outer can be same or be different.This research work may provide a method for obtaining far-zone scattered field with hollow distribution.