数字相位共轭二次谐波显微成像技术研究

Second harmonic imaging microscopy, which has the advantage of high three-dimensional resolution, has been a powerful tool to observe biological processes of tissues and cells. In the course of second harmonic imaging directly through biological tissue, elastic scattering is the dominant factor limiting the optical imaging resolution and imaging depth in tissues. Optical phase conjugation is known to be able to time reverse the scattering process and heal wavefront distortions. In this project, we propose a second harmonic imaging microscopy based on turbidity suppression by optical phase conjugation. This method, which is based on digital phase conjugating of second harmonic radiation, suppresses scattering efficiently to reconstruct the second harmonic emitting source, and offers high spatial resolution and high imaging depth. The study includes: Investigation of second harmonic emitting efficiency of single nanoparticle. The ballistic photons and diffused photons are timely resolved by ultrafast Kerr shutter, and these two components are processed to the investigation of single-noise ratio through optical phase conjugating, respectively. Controlling the spatial location of biological tissue through a micro-displacement platform to simulate the second harmonic conjugation path changes caused by the movement of the biological tissue, the lateral dynamic imaging range and axial imaging depth are investigated, respectively. This method is also studied the applicability in vivo biological tissue microscopic imaging.

纳米颗粒标记的二次谐波显微成像技术具有三维空间高分辨率优点，已成为观测生物组织和细胞生命过程的有力工具。在直接透过生物组织成像的过程中，散射成为限制提高二次谐波成像分辨率和成像深度的主要因素。光学相位共轭过程具有对散射过程的时间反演性，并可以纠正二次谐波波阵面畸变。为此，本项目提出了一种数字相位共轭二次谐波显微成像技术。该技术采用数字方式记录和产生相位共轭波，进行二次谐波发射光源图像重构，达到抑制生物组织散射目的，具有空间分辨率高、成像深度深的优点。主要的研究内容包括：单纳米颗粒二次谐波发射效率研究；利用超快光克尔门技术分别选通散射二次谐波中的弹道光与扩散光成分，研究不同散射光成分的重构图像信噪比；搭建控制生物组织空间位置的微位移平台，模拟生物组织运动造成共轭二次谐波传输路径的变化，研究系统的横向动态成像范围和纵向成像深度，探索该系统对活体生物组织显微成像的适用性。

基于纳米颗粒标记的相位共轭二次谐波显微成像技术具有三维空间高分辨率的有点，在生物成像领域有重要的应用前景。本项目开发了液相离子交换、飞秒激光直写诱导等技术，制备合成多种具有非中心对称纳米颗粒，并进行二次谐波发射特性研究。通过偏振依赖的二次谐波发射效率研究进行特定方位的二次谐波激励，获得较高效率的二次谐波发射方式。建立具有时间分辨率达150 fs的超快光克尔门技术，从时间上区分纳米颗粒发射二次谐波经散射体散射后的弹道光成分和扩散光成分。利用蒙特卡罗法模拟二次谐波穿透散射介质的横向二维光场分布，从空间上表征弹道光成分和扩散光成分的传输特性。建立二次谐波相位共轭显微成像系统，通过利用散射介质模拟生物组织，获得纳米颗粒的二次谐波共轭成像图。利用数字编程的空间光调制器记录二次谐波波前相位并共轭反射进入散射介质进行显微成像，成功抑制散射引起的成像空间分辨率下降问题，大大提高了成像信噪比。通过该项目的支持，我们研制多种具备高二次谐波发射效率的纳米材料，并进行相位共轭二次谐波的成像研究，对未来生物活体的动态标记成像具有一定的指导意义。