Research On Focusing And Image Recovery Algorithm For Random Scattering Optical System

With the rapid development of nanoscience and high-resolution imaging and detecting technology,the requirement for observation and imaging of microscopic world on nanoscale is getting more and more urgent.People hope to reveal the life process in cell and the microstructure of materials at the molecular level.In recent years,there emerges a series of novel techniques which can focusing and imaging beyond-diffraction-limit through random scattering media,thus overcoming disadvantages of low resolution and limited observation depth of traditional optical system when imaging through scattering media.Therefore,these kinds of new technologies possess important research significance in the field of biomedical sciences,life sciences and materials science and so on.Starting from the propagation model of light through random scattering medium,along with corresponding theories in statistical optics and Fourier optics,the process of focusing beyond-diffraction-limit in random scattering optical system has been simulated,and a systematic research on the process has been made.Moreover,the feedback control algorithms for phase-modulation-focusing and amplitude-modulation-focusing as well as the image restoration algorithm of object from its speckle pattern have been improved in the thesis.The following shows the research work in detail.1.Circular complex Gaussian distribution matrix in statistical optics is utilized to model the propagation of light in random medium,combined with Rayleigh-Sommerfeld diffraction and the phase modulation function of lens in Fourier optics,the process of propagation of light in random scattering as well as focusing of light through scattering medium beyond diffraction limit with wavefront-phase-modulation have been simulated.This kind of simulation method has the advantages of high precision,fast speed and low cost,and its simulation results are in good agreement with theoretical predicted results.This kind of simulation framework can be utilized to simulate the process of focusing and imaging through scattering medium,and to test and analyze the performance of focusing and imaging with different algorithms under variant parameters.Moreover,the above simulation framework can be used to explore new algorithms so as to improve or promote the performance of existing focusing and imaging technologies.In addition,the proposed simulation framework can also be employed to explore and study new kinds of techniques for focusing and imaging through scattering medium.2.A technology that utilizes curve fitting approach for focusing of light through turbid medium with wavefront phase modulation is proposed,according to the fact that the target intensity varies sinusoidally/cosinusoidally with the modulating phase,in which the Levenberg–Marquardt algorithm is introduced into the feedback control procedure to seek the optimal wavefront.The proposed technology shows high robustness to noise and can provides fine focus spots.Moreover,the curve fitting strategy adopted is able to dramatically shorten the wavefront optimization time for a single SLM segment,thus greatly boosting the speed of focusing.The proposed approach is suitable for fast focusing through scattering medium in the presence of heavy noise,and might help to focus light through dynamic turbid medium.3.Continuous sequential algorithm,which is used as the feedback control algorithm for focusing by wavefront amplitude modulation,has poor anti-noise performance and slow convergence rate.To overcome the drawback of continuous sequential algorithm,a technology that employs the genetic algorithm for focusing of light with amplitude modulation is put forward,in which the genetic algorithms is introduced to shape the wavefront amplitude of incident light.With the help of its characteristic global optimization strategy,the amplitude of all the grids can be simultaneously optimized so that the algorithm can quickly reach convergence point,and the sensitivity of the focusing process to the noise is greatly reduced.In consequence,the propose approach can provide a focus intensity that is nearly insensitive to noise,and is especially suitable for focusing of light in highly noisy environments.4.In the technology of imaging through scattering medium that is based on the spatial optical transmission matrix,the images restored by traditional Tikhonov regularization method usually have blurred edges and details,and the reconstruction results are usually polluted by heavy noise.Hence,a technology that utilized TVAL3 algorithm to recover the object from its speckle pattern is proposed,in which the TVAL3 algorithm is employed to reconstruct the target image.TVAL3 algorithm can not only effectively suppress noises,but also retain more image edges and details.The target can be well restored by the TVAL3 algorithms even high-level noise environment,and the image quality of reconstruction results obtained by TVAL3 is far better than that by Tikhonov regularization.