Optical Computed Tomography Apparatus using Optical Nonlinear Effect

点击翻译按钮获取中文摘要

1. Only coherent component in the light transmitted through a scattering medium produces the second harmonic light by mixing with pump beam in a nonlinear crystal. Before the experiment of optical mixing, the light traveling along the straight line in the scattering medium was extracted by the method utilizing the coherence of light (light polarization). The transmitted light intensity was measured as a function of the concentration of the scattering medium. The follr level of the transmitted light due to diffused light was significantly suppressed by detecting photons preserving initial polarization.2. The light pulse (2ps) from a mode-locked Ti : sapphire laser was divided into a pump beam and a probe beam. The probe beam transmitted through a scattering medium and the pump beam were mixed in BBO crystal. The peak intensity and the correlation width of the second harmonic light pulse was measured as a function of the concentration of the model scattering medium. The correlation width did not depend on the concentration of the scattering medium. The peak intensity linearly changed with the concentration of the scattering medium on the logarithmic scale as low as -85dB.These results showed that the light component traveling nearly along the straight line in the scattering medium was extracted by the optical mixing.3. The optical components used for the primary experiment were assembled on a board. The rotationtranslation stage was attached on the board to take the projection data of the sample from different directions. As a mode-locked YVO4 laser with sufficient peak intensity was not able to be developed, a mode-locked Ti : sapphire laser was used as a light source. The projection data of the absorbers in the scattering medium were taken by this apparatus. The clear CT image of absorbers was reconstructed from the projection data.