Fastcalculation And Application Of Partially Coherent Tighgly Focused Beams

When the light beams pass through the lens,it will focus.In life,if we put the lens under the sun,the light beams will focus on a point,which called the focus.The distance between the lens and the focus is called the focal length.In general,the focus of ordinary lens is between a few centimeters and tens of centimeters.When the focal length is only a few millimeters,we call this kind of focus tight focusing.Researchers are paying more and more attention to the tight focus spot,and the nature of the focus depends largely on the incident light.Therefore,many researchers have studied the focusing characteristics of different types of incident beams.In this paper,the propagation characteristics of partially coherent beams passing through a tightly focused system are studied by making use of a fast calculation method.Firstly,in the light source plane,we use the method of random phase screen expansion to expand the partially coherent light source into the incoherent superposition of multiple completely coherent sub light sources,and then transmitting the obtained completely coherent sub light source through the tight focus system.By using the Richards-Wolf diffraction integral formula,we can simplify the complex propagation formula of completely coherent light passing through the tight focusing system into a simple form of two-dimensional Fourier transform.At the same time,we can obtain the random electric field distribution of completely coherent light near the focal plane.Finally,we will carry out the incoherent superposition to study the statistical characteristics of partially coherent light in the focal planeIn chapter 1,we mainly review the development of the theory of partially coherent light and tight focusing,and the development of partially coherent tight focusing.In chapter 2,the basic knowledge of the theory of partially coherent light and tight focus are introduced.For partially coherent light,we use cross spectral density function or cross spectral density matrix to express it.For fully coherent light passing through a tightly focused system,we can transform the complex Richards-Wolf diffraction integral formula into a simple two-dimensional Fourier transform.For the transmission of partially coherent light through a tightly focused system,we use the method of mode expansion to combine the two methods.Finally,the convergence of the fast caculation algorithm and the tightly focused characteristics of the beam under different correlation functions are analyzed.In chapter 3,we introduce the self-healing characteristics of partially coherent radial polarized multi-Gaussian Schell mode beams passing through a sector of opaque obstacles.In this case,we use the fast algorithm proposed before.We study the self-healing characteristics of different coherence lengths under different obstacles.In chapter 4,we draw the conclusion of thesis and illustrate some prospects.