Research On Focusing Of Scattering Media Based On Wavefront Feedback Shaping Technology

Due to the scattering effect of the scattering medium,the laser light undergoes multiple scattering through the scattering medium and loses the original spatial information,thereby forming speckles,which has a serious impact on the ability of people to extract effective information from them.For example,in the field of satellite remote sensing imaging,light reflected from ground targets will scatter with the presence of a large amount of dust and other particulate molecules in the atmosphere,resulting in inability to image;in the non-invasive transmissive biomedical imaging applications,due to the scattering of particles inside the biological tissue,the imaging quality is inversely proportional to the thickness of the biological tissue,and it is difficult to perform deep imaging on the biological tissue.In order to overcome the scattering effect of the scattering medium,the focusing of the laser by the scattering medium is studied in this paper.The following research work is completed in this paper:1.The charge-coupled devices,liquid crystal spatial light modulators,and digital micromirror arrays used in the scattering medium focusing system are introduced.The working principles and the specific parameters of each device used in the experiment are given.2.The propagation model of light waves in scattering media is introduced.Including the propagation theory of light waves in the medium,the light intensity transfer function and the optical transmission matrix,the principle of the random medium transmission matrix and the measurement method under the random complex matrix model are introduced.3.A liquid crystal spatial light modulator is used to focus the laser light through the scattering medium.The continuous sequence algorithm was used to achieve the theoretical simulation and experimentation of the focusing,and the improvement was made on the basis of the algorithm to obtain a uniform area focused spot.For large-scale optimization problems,the theory of genetic algorithms was introduced and theoretical simulations were carried out to obtain a good focusing effect.At the same time,a contrastive analysis of the two enhancements under different noise conditions was conducted.4.The laser is focused by the scattering medium based on the modulation of the digital micromirror array.Due to the fast response speed and the high utilization of light energy of digital micromirror arrays,the use of digital micromirror arrays to rapidly modulate the incident wavefront has been investigated in comparison to the problem of slower modulation of liquid crystal spatial light modulators.5.Analysis of experimental error.Experiments have analyzed the thermal noise of the laser and CCD.In the local optimal scheme,the influence of the attenuation of the laser intensity on the selection of the optimal phase of a single modulation unit in the experiment is negligible.By analyzing the thermal noise of the camera,it is known that the noise is randomly distributed,and the CCD noise has little effect on the result.