基于激光诱导热透镜效应的光流控光束成形技术研究

Optofluidics is an emerging technology that aims to synergize optics and microfluidics. In-plane beam shaping is the base for the manipulation of light in optofluidic systems and has paramount importance to many applications such as input/output optical coupling, in-plane optical trapping, etc. The prevailing tunable liquid lens method relies on external flow pumps to adjust the focusing properties and suffers from slow response (~ 1 s) and many other drawbacks, presenting key limitations for microfluidics to exerting its full potential in optical functionalities. This project proposes a new beam shaping method based on laser-induced thermal lens effect. This method utilizes a continuous-wave pump laser and shines it onto a metal structure patterned on the substrate of optofluidic waveguide. The metal absorption heats up the fluid, the thermal diffusion together with the motion of fluids generate a gradient-index profile to diverge/converge the probe laser. This method can be envisioned to have a much faster response speed (<10 ms) and to possess other merits such as non-contact remote control, flexible relocation of point of interest, support of homogeneous fluid, easy integration with current microfluidic systems and so on. The research topics cover mainly: (1) theoretical analysis and numerical computation of laser-induced thermal lenses; (2) experimental verification of theoretical models and demonstration of basic beam shaping functions; and (3) optimization and demonstration of aberration-free thermal lenses. Our pilot studies have already shown controllable beam divergence and convergence, which lay a solid foundation for this project.

光流控学是新兴的一个学科，致力于光学和微流控学的有机集成。二维液体波导面内的光束成形，是光流控系统中光场调控的基础技术，对于输入输出耦合、面内光镊等应用具有重要意义。然而，目前基于变焦距液体透镜的光束成形技术，依赖外界液泵，具有响应慢（约1s）等缺点，严重制约了微流控系统发挥在光学应用的潜力。本项目提出基于激光诱导热透镜效应的光束成形新技术，利用液体波导基底上的金属图样吸收泵浦激光提供热源，结合液体的流动产生渐变折射率分布，以调控探测光的发散和会聚。此方法大大提高了响应速度（<10 ms），并具有非接触式调节、操控点灵活可变、容许使用均一液体、易于与现有微流控系统集成等优点。研究内容包括：（1）激光诱导热透镜的理论分析和数值模拟；（2）理论模型实验验证和光束成形基本功能的实现；（3）无像差热透镜的优化设计和实现。先期开展的预研工作已经成功观察到可调的光束发散和会聚，为本项目打下良好的基础。

光流控学通过有机地结合光学和微流控学，来发挥两者的优点。其中一个基础技术，就是进行二维液体波导面内的光束成形，对于输入输出耦合、面内光镊等应用具有重要意义。然而，目前基于变焦距液体透镜的光束成形技术，依赖外界液泵，具有响应慢（约1s）等缺点，严重制约了微流控系统发挥在光学应用的潜力。本项目提出基于激光诱导热透镜效应的光束成形新技术，利用液体波导基底上的金属图样吸收泵浦激光提供热源，结合液体的流动产生渐变折射率分布，以调控探测光的发散和会聚。此方法大大提高了响应速度（<10 ms），并具有非接触式调节、操控点灵活可变、容许使用均一液体、易于与现有微流控系统集成等优点。研究成果主要包括：（1）激光诱导热透镜的理论分析和数值模拟；（2）理论模型实验验证和光束成形基本功能的实现；（3）无像差热透镜的优化设计和实现。已发表19篇期刊论文，分别发表在Lab on a Chip，Light: Science and Applications等，其中两篇文章被选中封面内页或者封底，并获得了3项国际会议最佳论文。