A Study On Lensless Scattering Imaging Based On LED Illumination

The incident light will be scattered away due to the inhomogeneity of the refractive index in many materials, such as biological tissue opaque, white paint, or foggy, which will greatly degrade the imaging resolution and reduce the imaging depth, so that we cannot observe the expected targets through such materials with conventional optical imaging system. Therefore, study on how to achieve high resolution imaging through a turbid medium has important physical significance and application value for many areas, like biomedical imaging, public security, and anti-terrorism. Meanwhile, it is truly a great breakthrough in the field of optical imaging.We mainly introduce the theories and the experimental methods, which is the imaging through strongly scattering layers by speckle correlations, in this thesis. As a new system of optical correlation imaging method, put forward in recent years, it builds optical imaging theory model by use of the strongly scattering properties of turbid media, combined with the optical memory effect(OME). Further, this method realizes high resolution imaging, based on the correlative calculation and the reconstruction algorithm, which is high efficiency and high robustness. Imaging process of this method is not only because of the interference of the turbid media no longer to clear imaging, but also make full use of the characteristics of the turbid media to achieve high resolution imaging. It has many advantages, such as the simple theoretical model, no lens aberration, real-time imaging, and is a breakthrough in the field of scattering imaging.After demonstrating and testing the feasibility of imaging through strongly scattering layers by speckle correlations, we further proposed a speckle correlation imaging method based on OME theory with LED source, and we make the detailed introduction and related experiments from the imaging theory model, the experiment system and the reconstruction algorithm and so on. Comparison, the scattering imaging method of no lens with LED illumination has many advantages in many ways. Firstly, the imaging spectral width of the light source is no longer restricted, because the narrow spectrum is replaced by the wide spectrum, and it has realized the small depth of field imaging, make it have the certain vertical depth imaging. Secondly, the LED lighting takes the place of the extremely narrow incoherent light, which combines high performance single frequency laser with rotating ground glass, this change makes its imaging system structure simple, easy realization, lower cost, easy to obtain, high practicability. Lastly, in order to ensure the convergence rate and speed up the imaging process, the improved generalized approximate message passing(GAMP) in this project employs the sparse information as the prior knowledge and then combines with the compressed sensing theory to reduce the sampling data to achieve high efficiency and high robustness reconstruction.Through research and experimental verification, the speckle correlation imaging method based on OME theory with LED source lays the foundation for studying the principles of scattering imaging through turbid media with broadband light source, which will extend the applications of scattering imaging further.