High Contrast Imaging Through Scattering Media Using Structured Illumination Fourier Filtering

Sammanfattning: In imaging, obtaining high contrast is of great importance. When imaging through scattering media, optical filtering techniques are used to filter out multiple light scattering which causes loss of contrast. Imaging through scattering media is used in Bio-Medicine when looking through human skin; in characterization of spray systems in Combustion Engineering as well as in other applications where visualization within fog, smoke or turbid water is necessary. This project focuses on the development of a novel optical filtering method called Structured Illumination Fourier filtering, or SIF. It is shown here that SIF can achieve high contrast imaging using visible light through a scattering medium of optical depth up to OD = 15. Measurements are performed through a water dispersion of polystyrene spheres of D = 0.13 μm. The performance of SIF is compared to the individual performances of Fourier filtering and Structured Illumination. SIF is shown to outperform these techniques in optical depths above OD = 10. A common way to increase contrast through a given scattering medium with small particles is to use a longer wavelength. It is shown here that SIF can achieve equally high contrast through a medium using blue, green and red light. Also, a comparison between the recorded images and simulations from the newly developed online Monte Carlo software Multi-Scat shows great promise for the validation of the software.