| The grating imaging system has the advantages of high resolution,high sensitivity,and strong anti-interference ability,and has been widely used in fields such as machine vision,biomedical imaging and spectroscopy.Early studies on grating imaging systems mainly considered the coherence or polarization characteristics of the light field,but these two characteristics of the light field have different effects on the grating imaging system,so considering only one characteristic of the light field is not enough.This paper is based on the polarization coherence unified theory to study the polarization system of partially coherent light illuminated gratings,establish a physical image relationship model of partially coherent light illuminated grating polarization system,obtain theoretical results by simulating the model,design and build an experimental platform,acquire and process experimental data,compare and verify the experimental results with the theoretical results to draw conclusions.The specific research contents of this paper are as follows:(1)Design a simple diagram of the optical path of the polarization system for partially coherent light illumination of a grating,and establish a mathematical model based on the Van Cittert-Zernike theorem for scalar system without considering polarization.In addition,this paper adopts the polarization coherence theory to apply the generalized Stokes parameters and extend the scalar system’s object-image intensity relationship to the polarization vector system.Finally,derive the polarization system’s object-image space and frequency domain relationships for the partially coherent light illumination grating.(2)Simulate and model the object-image relationship of a partially coherent light grating polarization system by MATLAB.Based on the established transfer cross coefficients in the object-image relationship,the simulation results show that under the same coherence,the decay rate of the second harmonic coefficient is faster than that of the first harmonic and DC component.The model of the first and second harmonic apparent transfer function is simulated,and the results show that under incoherent light field,σ=0,the apparent transfer function of the first and second harmonic exhibits linear variation.As the coherence increases,the apparent transfer function deviates from the linear relationship.Based on the simulation of the object-image domain model of a sinusoidal amplitude grating polarization system under partially coherent light illumination,this paper obtains the Stokes intensity distribution of one-dimensional image of the sinusoidal amplitude grating for three different coherences.The simulation results show that the spatial domain image Stokes intensity distribution is related to the inherent frequency and coherence of the grating.Simulation of the frequency domain physical and image relationship is conducted for four special parameters,and the results show that when the natural frequency of the grating is T(fx0)=0.8,and the value of σ changes from 1 to 0.5,coherence increases,the first harmonic disappears.(3)An experimental study was conducted by using a time-resolved polarization imaging system to investigate the polarization properties of partially coherent light illuminating gratings.The experimental setup included two sinusoidal amplitude gratings with different line densities of 20 lines/mm and 50 lines/mm.The obtained experimental data was analyzed and processed by MATLAB.The results showed that when the natural frequency T(fx0)=0.8 of the grating and the parameter σ changed from 1 to 0.5,only the DC component remained and the first harmonic disappeared,which was consistent with theoretical predictions.This paper presents a method for investigating polarization systems of partially coherent light illumination and transmission through objects,which is not only applicable to the grating object studied in this article.Additionally,this study combines the coherence and polarization properties of the light field to expand the evaluation method of imaging quality.Therefore,this research has broad prospects for applications in optical measurement,image enhancement,and medical diagnosis. |
