Research On Focusing Method Of Penetration Scattering Medium

For scattering media with uneven refractive index,such as paint layers,clouds,dense fog,etc.,the medium particles disrupt the light propagation,generate random speckles and cause the target objects behind the medium to be unable to be identified.The scattering medium is generally considered to hinder optical focusing and imaging.However,multiple scattering process is deterministic.Based on this characteristic,many methods have emerged.The advantage of wavefront shaping technology is that the optical system is simple,its principle is easy to implement,and the real-time performance is impressive.Therefore,in deep tissue microscopic imaging,single-fiber endoscope,scanning imaging and many other fields have important research value.Based on existing methods,this paper proposed an improved fast focusing method,and realized single/multipoint focusing and imaging.This paper is organized as follow:1.The transmission model of light waves in homogeneous and inhomogeneous media is derived.On this basis,a detailed analysis of the linear mathematical expression of scattering is carried out,and the feasibility of wavefront shaping methods is theoretically proved and is able to achieve ultra-diffraction limit focusing and focusing through multimode fiber.It provides a theoretical basis for the subsequent research on the wavefront shaping method based on the iterative optimization algorithm.2.We propose a differential evolution algorithm(DEA)-based wavefront shaping optimization method to achieve faster focusing and higher enhancement.DEA uses multiple masks in parallel to alleviate the shortcomings of traditional optimization algorithms that may fall into local optimality and adopts a greedy selection strategy,which gives DEA a certain advantage in convergence rate.3.Through simulation and optical experiments,we realized single-point focusing,multipoint focusing and imaging through scattering medium.The maximum experimental enhancement for single-point focusing can reach 52.551.Results prove that DEA performs better than existing algorithms.4.We built the experimental optical setup and realized focusing through stable medium-three-layer ground glass and a multimode fiber of the laser with a wavelength of 532 nm.The focusing performance and related parameters were analyzed.