Holographic time gate investigations and confocal techniques.

Abstract

Image formation through scattering media is one of the most challenging problems of modern image science. This dissertation explores new ideas on two different approaches to this problem, photon migration and coherence optical sectioning. In the former, the aim is to transmit short coherence light through a highly scattering medium, such as thick biological tissue, separate that light that takes the shortest path through the medium, and use this so-called first arriving light to form an image of the structures embedded in the medium. In the second, light is either transmitted through or reflected from a thick medium, an imaging system is focused on a plane within the medium, and coherence methods are employed to reject light that is scattered by structures lying within the medium but outside the plane of interest. In the area of photon migration, the research reported here consisted of new photon migration methods and a new method of analysis, using a Fourier optics approach instead of the traditional methods, such as transport theory, which are quite complicated. The new analysis method predicts in a relatively simple way the resolution capabilities of the photon migration process as a function of the medium thickness, the mean-free-path of the photons between scattering events, and various other parameters. Computer simulation programs were developed to test the new imaging methods and to verify the correctness of the new theory. In the area of coherence optical sectioning, new methods were developed to achieve the optical sectioning, using light that is either spatially or temporally incoherent. A generalized analysis was made. Various system configurations were developed and experiments were carried out to produce optically-sectioned images using biological samples. Also, an analogy between two rather different imaging methods, synthetic aperture imaging, and confocal imaging was developed. In this analogy, confocal imaging was seen to be a limiting case of synthetic aperture imaging. All of the work was related in some degree to holography; for example, coherence confocal methods were produced by the process of low coherence image plane holography, and spectral holography was used to create a 3-dimensional surface map of reflective objects. Indeed, holography is the thread which ties all of the work together.