New Principle for Optical Tomography Based on Synthesis and Control of a Three-dimensional Spatial Coherence Function : A Basic Research

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The purpose of this research project is to establish the basis of a fundamentally new technique for synthesis and control of spatial coherence function, which enables selective creation of high coherence between a pair of desired points in three-dimensional space. Because the proposed technique uses spatial (rather than temporal) coherence function of a quasi-monochromatic light source, it opens up a new avenue to optical coherence tomography that is completely free from the dispersion problems that are unavoidable in the existing techniques of low-coherence tomography.The main achievements are summarized as in the following :1. A theory and a methodology for designing a source distribution that produces a desired distribution of a spatial coherence function in three-dimensional space were established. In particular, a new model of fringe formation was proposed that gives a clear and intuitive picture about the relation between the source shape and the three-dimensional coherence structure.2. A new principle for the simultaneous sensing of the object distance and the local inclination of the object surface was proposed, and the validity of the principle was verified by experiment.3. A new scheme of phase-shift technique based on a source shape modulation by means of a spatial light modulator was proposed and verified by experiment. The proposed scheme enables phase shift completely free from a mechanically moving component, such as a piezo-electric transducer or a precision stage.Integrating all the above results, a new sensing system was developed that successfully demonstrated the shape measurement of three-dimensional structure made of a set of standard gauge blocks.