Optical Computed Tomography Apparatus using Optical Nonlinear Effect

1. 在非线性晶体中，通过散射介质的光只有相干分量与泵浦光混合才能产生二次谐波光。在光学混频实验之前，利用光的相干性（光偏振）的方法提取在散射介质中沿直线传播的光。透射光强度作为散射介质浓度的函数进行了测量。由于漫射光引起的透射光的后续水平被检测光子显著抑制，保持了初始偏振。锁模钛蓝宝石激光器的光脉冲（2ps）分为泵浦光束和探测光束。通过散射介质传输的探测光束和泵浦光束混合在BBO晶体中。测量了二次谐波光脉冲的峰值强度和相关宽度与模型散射介质浓度的关系。相关宽度不依赖于散射介质的浓度。峰值强度随散射介质浓度在对数尺度上呈线性变化，低至-85dB。结果表明，通过光学混合可以提取出在散射介质中近似沿直线传播的光分量。用于初级实验的光学元件组装在一块板上。在板上安装旋转平移台，从不同方向获取样本的投影数据。由于无法开发出具有足够峰值强度的锁模YVO4激光器，因此采用了锁模Ti：蓝宝石激光器作为光源。利用该仪器采集了吸收体在散射介质中的投影数据。根据投影数据重建吸收体清晰的CT图像。

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.