Optical Computed Tomography Apparatus using Optical Nonlinear Effect

1.光在非线性晶体中与泵浦光混合后，只有相干光通过散射介质才产生二次谐波。在光混频实验之前，利用光的相干性（光的偏振性）提取出在散射介质中沿着直线传播的光。测量透射光强度作为散射介质浓度的函数。通过检测保持初始偏振态的光子，由于漫射光引起的透射光的后续能级被显著抑制.从锁模钛宝石激光器输出的光脉冲（2 ps）被分成泵浦光和探测光。通过散射介质的探测光与泵浦光在BBO晶体中混合。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。峰值强度与散射介质浓度在对数尺度上呈线性关系，最低可达-85 dB，说明光混频提取了散射介质中近似沿着直线传播的光分量.用于初步实验的光学元件被组装在板上。旋转平移台安装在板上，从不同方向获取样品的投影数据。由于不能开发出具有足够峰值强度的锁模YVO 4激光器，因此使用锁模Ti：蓝宝石激光器作为光源。利用该装置拍摄了散射介质中吸收体的投影数据。由投影数据重建出清晰的吸收体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.