飞秒光镊中的非线性光学效应研究

Optical tweezers are currently used for noncontact particle manipulation in physics, chemistry, and biology. Its principle is based on the interaction between optical electric fields and induced linear polarization. Optical trapping using low-power high-repetition-rate femtosecond laser pulses, which could study the optical trapping dynamics, has a higher trapping efficiency than that of the conventional CW lasers to trap particles. In this project, we will investigate novel light forces and nonlinear optical effects in the optical trapping processes, based on the nonlinear polarization for the interaction of femtosecond laser pulses with nanoparticles. We focus our attention to investigate the interaction of femtoseocnd laser pulses with nonlinear optical nanoparticles. Firstly, the dependence of optical forces on geometrical size and nonlinear optical characteristics of nanoparticles will be studied. Secondly, the stable trapping and manipulation of nonlinear optical nanoparticles will be realized, and the corresponding nonlinear optical effects will be measured. Thirdly, the nonlinear optical characterizing technique on a single nanoparticle will be developed. Lastly, optical tweezers for trapping nonlinear optical nanoparticles will be improved. By performing this project, the nonlinear polarization theory for the interaction of intense laser light with nanoparticle will be established and developed. The novel light forces originated from the nonlinear polarization will be analyzed and identified. Correspondingly, the novel nonlinear optical effects will be found. Besides, the technique for characterizing the nonlinear optical effects on a single nanoparticle will be developed and improved. Nonlinear optical trapping will be exploited for applications in bio-photonics and super-resolution imaging.

光镊广泛用于物理、化学和生物等领域的非接触微粒操控，其基本原理是基于光场与微粒相互作用和感应线性极化。相比于连续激光，低功率高重复频率飞秒激光脉冲捕获微粒具有更高的捕获效率和可研究光捕获动力学等优点。本项目基于飞秒激光脉冲与纳米粒子相互作用过程中的非线性极化理论，研究光学捕获过程中新颖的光力和非线性光学效应。围绕飞秒激光脉冲与非线性光学纳米粒子相互作用，研究光力分布与粒子的几何尺寸和非线性光学特性等的依赖关系，实现对非线性光学粒子的稳定捕获与操控，测量光学捕获过程中新颖的非线性光学效应，发展单粒子非线性光学表征技术，完善基于捕获非线性光学纳米粒子的光镊技术。通过本项目的实施，建立和发展强激光与纳米粒子相互作用的非线性极化理论；分析和鉴别非线性极化导致的新型光力，期待发现新颖的非线性光学效应；发展和完善单粒子非线性光学表征技术，探讨非线性光学捕获在生物光子学和超分辨成像等方面的应用。

光镊是一种利用聚焦的激光束对微纳粒子进行非接触无损伤操控的一门技术。该技术广泛应用于物理、化学、生物、材料等学科领域。在光镊技术中，人们通常用连续激光束稳定地捕获微纳粒子。近年来，研究者用高重复频率飞秒激光脉冲替代连续激光，发展了飞秒光镊技术，并且发现了多种新颖的实验现象。. 在本项目的资助下，课题组围绕飞秒光镊中的非线性光学效应，研究光学捕获过程中新颖的光力和非线性光学效应，取得了如下阶段性的科研成果：.（1）多种新型矢量光场的聚焦传播特性。研究了一阶拉盖尔高斯光束、二阶全庞加莱光束、杂化柱状矢量涡旋光束等在自由空间或通过非线性光学介质后的聚焦传播特性，探讨了部分光束在光学捕获中的应用。.（2）光场的线动量和角动量特性。利用幂指数角向变化矢量光场实现了被捕获粒子做不对称旋转和轨道运动；研究了椭圆偏振涡旋光束在二次谐波过程中的角动量守恒问题；报道了分数阶矢量光场在聚焦场中的角动量空间分离特性。.（3）多种新颖的非线性光学效应。研究了诸如各向异性非线性折射、局域和非线性局域非线性共存、纳米结构中的二次谐波增强等多种非线性光学效应。.（4）非线性极化导致的新型光力。研究了聚焦飞秒激光脉冲作用在非线性光学瑞利粒子上的光力；利用周围环境的光学非线性效应实现了对瑞利粒子的光学牵引；基于飞秒光镊表征了单个纳米粒子的双光子吸收系数。. 通过本项目的实施，发展和完善了飞秒激光脉冲与非线性光学纳米粒子相互作用的物理模型、非线性极化理论和半解析的光力表达式；揭示了多种类型的非线性光学效应对光力分布和光学捕获的影响；基于光场调控技术研究了飞秒光镊中多种光束的粒子捕获动力学特性；发展和完善了利用飞秒光镊和光场调控表征单个微纳粒子的双光子吸收系数的方法。这些工作的完成为进一步开展飞秒光镊技术应用于非线性纳光子学、纳米材料的非线性光学表征和单粒子非线性光学成像等提供了较丰富的知识积累。