Multiple optical trapping based on high-order axially symmetric polarized beams

Multiple optical trapping with high-order axially symmetric polarized beams（ASPBs） is studied theoretically,and a scheme based on far-field optical trapping with ASPBs is first proposed.The focused fields and the corresponding gradient forces on Rayleigh dielectric particles are calculated for the scheme.The calculated results indicate that multiple ultra-small focused spots can be achieved,and multiple nanometer-sized particles with refractive index higher than the ambient can be trapped simultaneously near these focused spots,which are expected to enhance the capabilities of traditional optical trapping systems and provide a solution for massive multiple optical trapping of nanometer-sized particles.

Tight focusing of axially symmetric polarized vortex beams

Tight focusing of axially symmetric polarized vortex beams is studied numerically based on vector diffraction theory. The mathematical expressions for the focused fields are derived. Simulation results show that the focused fields and phase distributions at focus are largely influenced by both the polarization order and topological charge of the incident beams. Moreover, focal spots with flat-topped or tightly-focused patterns can be flexibly achieved by carefully choosing the polar- ization order and the topological charge, which confirms the potential of such beams in wide applications, such as optical tweezers, laser printing, lithography, and material processing.

Multiple 3D optical trapping using higher polarization order axially-symmetric polarized beams

We propose a novel single-beam multiple 3D optical trapping scheme using higher polarization order axially-symmetric polarized beams in an aplanatic focusing system. We calculate numerically the intensity distribution near the focus which presents a multi-focus-spot pattern and provides the possibility of multiple optical trapping. We also calculate the corresponding gradient force distribution near the focus. Finally we introduce a 3D optical chain by combining the single-beam system with a single diffractive optical element.

高级次轴对称偏振光束的聚焦特性及应用综述

高级次轴对称偏振光束具有更为复杂的偏振分布,在高数值孔径聚焦情况下可获得多个超小聚焦光斑,这样的聚焦特性使其在显微成像、材料加工、粒子捕获等领域体现出一定的应用价值,引起了广泛关注。综述了近年来关于高级次轴对称偏振光束的聚焦特性及主要应用的研究成果。介绍了高级次轴对称偏振光束的基本概念,并基于矢量衍射理论给出了聚焦场的数学表达式,最后介绍了该类型光束在粒子捕获与操控、并行光学显微成像方面的典型应用。

基于对称双模耦合器的波长可切换柱矢量光纤激光器

为了实现高纯度脉冲柱矢量光的输出,提出并搭建基于对称双模耦合器的波长可切换的被动锁模柱矢量全光纤激光器。根据光纤传输原理得到基模向高阶模转换的折射率匹配直径,运用模式耦合模理论及光束传播法模拟分析了对称双模耦合器的结构参数对模式选择及耦合特性的影响,采用熔融拉锥法并免去传统的模式选择耦合器制作上的预拉锥工艺制作了对称双模耦合器,通过搭建一套被动锁模柱矢量全光纤激光器实现了中心波长1039 nm和1068 nm可切换、脉冲时间间隔为113.8 ns、重频为8.78 MHz、脉宽660 ps/656 ps、最大输出平均功率为5.25 mW/5.2 mW、模式纯度大于97%的柱矢量光输出。实验验证了对称双模耦合器的可行性,为后续高纯度柱矢量光的获得提供一种可行的方案。

基于少模光纤的轴对称偏振光束的产生

首先介绍了轴对称偏振光束的基本概念以及特性,然后以少模光纤为模式转换器,通过旋转偏振控制器上光纤挤压器的旋钮对光纤中间部分施加压力,同时配合旋转光纤挤压器,以实验的方式获得了不同模式的轴对称偏振光束。通过调节偏振控制器以及输入光束和光纤的离轴状态,分别得到了径向偏振TM01模式,角向偏振TE01模式,奇数混合偏振HEodd21模式,偶数混合偏振HEeven21模式,以及线偏振HE11模式五种光纤所激发的模式。同时,还通过干涉实验中叉形光栅结构证明了相位奇点的存在。

猫眼腔激光器光束合成轴对称线偏振矢量光束

提出了一种将猫眼腔氦氖激光器与马赫-曾德尔干涉仪相结合、通过模式叠加生成多种轴对称线偏振矢量光束的新方法。利用猫眼腔激光器获得了TEM00、TEM01、TEM10、TEM11、TEM20、TEM21、TEM30、TEM31等多种激光横模;利用马赫-曾德尔干涉仪通过模式叠加获得了四种不同形式的轴对称线偏振矢量光束,其偏振级次和初始偏振方位角分别为(+1,0°)、(+1,-90°)、(-1,0°)和(-1,90°);测量了生成光束经过线偏振片的强度分布,验证了生成光束的偏振分布特性。利用该方法可在同一系统上通过调制猫眼腔激光器生成多种形式的轴对称线偏振矢量光束,无需特殊光学元件,成本较低,操作简单。

Further generalization of Fermat's principle

From Maxwell’ s equations for electromagnetic fields, time-averaged energy flow density vector of stable monochromatic linearly polarized light in an isotropic insulative nonmagnetic medium is deduced. By the introduction of time-averaged energy flow density rays and the definition of new generalized refractive indexn G1, Fermat’s principle of geometric optics is further generalized and its application conditions are discussed. The generalized Fermat' s principle can be used to describe stable transmission of light in a medium with variable refractive index. The necessary and sufficient conditions of a nondivergent and nonfocusing light beam are derived from this Fermat’s principle.