Image Processing with White Light Broad Source Interferometry.

Abstract

This thesis is concerned with interferometric image processing techniques using radiation of reduced coherence. The interferometers are formed from diffraction gratings. The first half of the thesis extends the theory of diffraction grating interferometers, and the second half is concerned with applications. One of the major aims is to demonstrate, both theoretically and experimentally, the noise suppression capabilities that arise when these interferometer systems are adapted for operation with light of reduced coherence. In some cases, the illumination is spatially incoherent (i.e., derived from an extended source); in other cases, the illumination is temporally incoherent (i.e., derived from a spectrally broad source). The third order analysis for fringe formation is derived, showing how chromatic aberrations reduce the fringe contrast when broad spectrum or broad source illumination is used. Next, the theory of interferometric imaging of a distant object in white light is developed. Then, a wholly lensless imaging process is developed, comprising two grating interferometers in t and em. An experimental system was constructed to demonstrate the method. It is shown that the grating interferometric method has some significant advantages over conventional imaging processes when imaging through an inhomogeneous medium, such as the turbulent atmosphere. A new method of imaging through a phase-distorting medium is presented that involves collecting interferometric data at discrete points and using computer methods for solving a set of simultaneous equations. Coherent noise is often a serious problem in interferometers. By broadening the size of the illuminating source, a statistical averaging process is produced that leads to significant noise reduction. The theory of noise suppression by broad source interferometry is first developed and then applied to phase conjugation imaging, multicolor archival storage, image-plane multiplex holography, and double-exposure interferometry.