Three-dimensional tomographic imaging using wavelength-scanning laser and two-wave mixing and its applications to measurements

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This research deals analyses and experiments about gains of two-wave mixing using linear phase-modulated light whose phase changes repeatedly with a period in time. First, when a pump beam is linearly phase-modulated, time-varying intensity of the interference pattern in a photorefractive (PR) crystal contains zero frequency component which produces an index grating. The gain characteristics of the two-wave mixing depending on the amplitude of the zero frequency component are made clear. Next, the phase-modulation of a pump beam and a linear wavelength-scanning of a laser diode are used simultaneously to obtain tomographic images. Characteristics of the tomographic images are explained in detail through the gain characteristics. Finally, when the width of the wavelength-scanning is large, the amplitude of zero frequency component of the interference pattern differs within the PR crystal. It is shown that in this case the index grating is formed in a restricted region of the PR crystal. It is most suitable for the tomographic imaging to make an image of the object in PR crystal. We constructed an setup for the tomographic imaging to reconstruct images of patterns drawn on several sheets of polyvinyl chloride.