Holographic spatial and temporal coherence methods for optical discrimination.

摘要

In many imaging situations, whether it be the imaging of weakly scattering, multi-layered structures, or imaging through highly scattering, thick materials such as human tissue, it is often desirable to discriminate between light arriving from the object at various times or from various planes within the object structure. A major limitation of conventional imaging systems is that all of the light that enters the imaging lens is ultimately recorded. In many applications, this property produces ambiguous or even useless images.; This dissertation describes two approaches to isolating the desired image light from the remainder of the unwanted light. Approaches in the temporal domain make use of the fact that light traveling different optical paths will arrive at a detection plane at different times. Thus a gating mechanism can be employed to isolate the light that travels the path of interest. A novel technique, Fourier synthesis holography, is described in which a pulse is decomposed into its spectral components and a hologram is recorded for each component. These holograms are then read into a computer and a Fourier transformation is performed along the wavelength dimension. This procedure produces the required temporal gate, with the advantage that post-detection alteration of the shape and temporal position of the gate are possible. The advantages of this technique over other holographic techniques are described and demonstrated.; Methods for optical discrimination in the spatial domain are also described. Spatial domain techniques isolate light that at a given plane has spread the least. A system that utilizes a spatially broad, quasi-monochromatic source in an interferometer is shown to behave identically to a confocal imaging system. Because of the narrow bandwidth of the source, the system can be used both as a microscope and as a telescope. Additionally, an interferometric system is described that combines both spatially and spectrally broad sources. The depth discrimination of the system is analyzed in detail and a configuration is proposed that yields depth discrimination for the combined source which exceeds the sum of the two sources independently.