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

本文对相位随时间周期反复变化的线性相位调制光的二波混频增益进行了理论分析和实验研究。首先，当泵浦光被线性相位调制时，光折变（PR）晶体中的干涉图样的时变强度包含零频率分量，该零频率分量产生折射率光栅。明确了二波混频增益随零频分量幅值变化的特性。接下来，泵浦光束的相位调制和激光二极管的线性波长扫描被同时用于获得断层图像。通过增益特性来详细说明断层图像的特性。最后，当波长扫描的宽度较大时，干涉图样的零频率分量的幅度在PR晶体内不同。它示出，在这种情况下，在PR晶体的限制区域中形成的折射率光栅。在PR晶体中成像最适合于层析成像。我们构建了一个装置的断层成像重建图像的图案绘制在几张聚氯乙烯。

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.