太赫兹径向偏振光的宽谱调控研究

As an important technical approach for precise structure observation and material analysis in micro-nano scale, terahertz radial polarization has become a hot research topic in recent years. However, the low energy and the unadjustable frequency band limit its rapid development and application in various fields. At the end of 2016, applicant and members observed that there is a stable phase difference between the four quadrants signals of the terahertz polarized light. Importantly, this phenomenon is not affected by the exterior electric field. This provides a new idea for us: avoid destructive interference and promote constructive interference by choosing coherent terahertz part. Basing on the physical process of terahertz radiation from the femtosecond laser monochromatic filament, we want to use hollow-metal-waveguide-fiber and circular 3/4 quadrant electrode plates (with high pressure control), extending the length of laser filament and regulating the process of electron movement, in order to increase the energy conversion efficiency of terahertz radiation process and then enhance the energy of terahertz radially polarized wave. On this basis, research will be further explored in the gas filled hollow-metal-waveguide-fiber with high ionization threshold and pressure regulation scheme, in order to realize the stable amplification and frequency tuning of longitudinal terahertz wave. These results will provide the foundation for its application in super-resolution and vivo cell detections.

太赫兹径向偏振光作为微纳米尺度下精准结构观测与物质分析的重要技术途径，近年来迅速成为太赫兹领域的研究热点。然而，能量低和频段无法连续调节限制了其在各个领域的快速发展和应用。2016年底，申请人与团队观测到太赫兹径向偏振光四个象限的信号之间存在稳定的相位差，且不随外加高压电场的作用而改变。这一现象的发现为我们提供了一种新的思路：避开信号整体的相干相消，选择性放大相干部分的太赫兹波。因此，本课题预期基于飞秒激光拉丝辐射太赫兹波的物理过程，采用空心金属波导光纤和环形3/4象限的缺口型电极片(辅以高压控制)相结合的方法，延长激光成丝距离的同时调控电子的运动过程，用以大幅提升太赫兹波辐射过程的能量转换效率，实现能量增强。在此基础上，课题将进一步探索在空心金属波导光纤中充入高电离阈值的气体和调节气压的方案，以期实现太赫兹纵向波信号的稳定放大和频率调谐，为其将来在超分辨和活体细胞检测中的应用奠定基础。

本项目针对太赫兹径向偏振光能量低和频段无法连续调节的问题，通过：1）建立相关激光拉丝的实验调谐和传播过程的数值模拟，确认了太赫兹径向偏振光四个象限的信号存在稳定相位差的机制；2）结合电极片加高压控制的方法，完成了太赫兹径向偏振光能量增强的机理和相关实验研究；3）实现了调谐太赫兹径向偏振光中心频率的方法，分析了其非线性物理过程。整体研究过程按原项目计划进行，取得了预期的成果。相关理论模型和实验系统都已建设完成，发表标注国家自然基金资助的国际SCI论文18篇，EI论文5篇，获授权中国发明专利10项，美国专利2项，软件著作权3项，省部级技术发明奖一项，培养博士后1名，博士研究生1名，硕士研究生5名，参加国际会议做主题报告10次，国内会议做主题报告8次。该项目对后续激光拉丝产生并调控太赫兹纵向波信号的稳定放大和频率调谐有重要意义，并为其将来在超分辨和细胞检测中的应用奠定了经验基础。