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Assessing and Improving Algorithms to Control the Propagation of Light through Scattering Media

Fayyaz, Zahra | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50053 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Rahimitabar, Mohammad Reza; Nasiriavanaki, Mohammad Reza
  7. Abstract:
  8. Light propagation through turbid media, such as biological tissues, experience scattering due to inhomogeneous distribution of refractive indices of their microscopic structure. Scattering and diffusion of light not only limit many optical imaging techniques, but are also big challenges for telecommunication, spectroscopy, and other optical techniques. Recently many new imaging methods are developed that work in strongly scattering media such as optical coherence tomography, diffusion tomography, and laser speckle velocimetry. In this thesis, we have studied how wavefront shaping techniques can tackle the problem of scattering. By spatially shaping the wavefront of the incident beam, using digital micromirror devices (DMD) or spatial light modulator (SLM), the scattered light can be focused to a point. Various iterative optimization algorithms for obtaining the most optimum shape of the impinging light have been explored in several studies. So far, however, there has been little discussion on comparing these algorithms. In this study, we implement six optimization algorithms including continuous sequential, partitioning algorithm, transmission matrix method, genetic algorithms, particle swarm optimization and simulated annealing to obtain the optimum wavefront shape. The performance of the algorithms is compared in ideal and noisy conditions.In particular, simulated annealing (SA), which is a heuristic optimization algorithm is suggested for focusing light through a turbid media for the first time. A comprehensive guideline to define and set up the SA parameters is suggested. The results showed that the SA algorithm performs effectively in average measurement noise environments and has some advantages over the aforementioned algorithms
  9. Keywords:
  10. Spatial Light Modulator (SLM) ; Light Scattering Layer ; Simulated Annealing Method ; Biological Tissue ; Imaging Scattering Biological Tissue

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