非傍轴局域加速光束的产生及应用研究

In 2007, accelerating beams are first generated in three-dimensional space. As revolutionary tools, accelerating beams play important roles in several fields of scientific research because they can propagate stably along curve trajectories in free space. By contrast, classical light beams propagate along a straight path without regard for the broadening effects of diffraction. Paraxial accelerating beams have localized main lobes that are applicable in some research fields. However, their practical value is limited by their insufficient acceleration and weak ability to bypass objects..Lately, nonparaxial accelerating beams constructed in 2D plane, can freely bypass any obstacles since with great acceleration. However, such nonparaxial accelerating beams are impractical in research because their main lobes are 1D “light sheets”, instead of 2D localized main lobe. In other word, their main lobes are localized in one dimension during propagation, and another dimension is unlimited in space..Introducing canonical catastrophe theory and differential geometry theory into beam propagation theory and wave equation, we will generate nonparaxial accelerating beams with 2D localized main lobes. Their high-powered localized main lobes can propagate in the nonparaxial region along some curved propagating trajectories, including of parabolic, half-circular, circular or elliptical paths (i.e., self-rotating beams with “bullets” that are usually described in science fiction). As a singular and unique laser, the nonparaxial localized accelerating beam can be used as a modern and practical energy source or laser probe for future scientific applications. For example, their localized main lobes with high energy densities can bypass any obstacles, hence they can be exploited to precisely trap, sort, measure, mix, and manipulate micro-particles to follow curved trajectories in areas that light cannot directly reach.

作为可在自由空间沿弯曲（不是直线）轨迹传输的稳定光束，加速光束从07年诞生，就作为一种革命性工具在很多领域发挥作用。目前在三维空间产生的傍轴加速光束，虽有可实用的局域主锤，但它的加速度很小，绕过障碍物的能力有限，因而限制了使用范围。近期，人们在二维平面构建了几种非傍轴加速光束。纵然加速度很大，但它的主陲是一维局域另一维无限扩展的”光片”，并无实用价值。.本项目拟将规范突变论和微分几何等数学理论引入光束传输理论，在三维空间，实际构造轨道可控的非傍轴局域加速光束。这种光束，不仅具有能量集中的局域主锤，还可根据实验需要，灵活控制主陲，在非傍轴区沿任意不同轨迹传输，包括沿抛物、半圆、圆或椭圆轨迹传输（这是只有在科幻小说中才会出现的有“弹头”的自回转光）。这种光束，预期能为涉及光与物质相互作用的很多领域，提供新的奇异光源或激光探针。比如，就可绕过障碍物，在直射光束无法到达的区域进行微观操控和探测。

作为可在自由空间沿弯曲轨迹传输的无衍射光束，无衍射加速光束从2007年诞生以来，就作为一种重要的激光工具在很多领域发挥作用。针对构建具有非傍轴加速特性及无衍射传输特性的光束，本项目主要做了如下的一些工作。（1）、将规范突变论和微分几何等数学理论引入了到光束传输理论中，建立自加速光束与光束焦散线之间内在联系和理论模型。然后将任意自加速传输轨迹的光束在拐点处分解成多段单调曲线，并利用焦散线理论分别构建每段单调轨迹所对应的波前相位分布，然后利用相位的叠加原理，建立任意自加速光束传输轨迹与相位的数学模型。构造好的相位分布加工为相位掩膜板，实验产生了任意轨迹的非傍轴加速光束。这一方法打破以往自加速光束的多种制约，实现了光束沿任意轨迹传输以及光场灵活可控的目标，极大地拓展了自加速光束的应用潜力，预期能为涉及光与物质相互作用的很多研究领域，提供新的奇异光源或激光探针。比如，利用这类能沿弯曲轨迹传输的加速光束，就可绕过障碍物，在直射光束无法到达的区域进行微观操控和探测。（2）. 将具有弯曲传输轨迹的无衍射加速光束用于生物组织信息探测，探测深度获得了很大的提升。(3). 衍射是光波的基本传输特性，为克服光波的衍射，近年来引入和产生的无衍射结构光束，是构建传输不变无衍射光束的一种重要手段。为精确、高效的产生无衍射马蒂厄光束，首先利用虚源法，研究了无衍射马蒂厄光束的非傍轴传输特性。然后，利用稳相法，理论证明了锥镜合并振幅调制能够产生马蒂厄光束的理论机制。随后，利用胶片输出仪制作了具有角向马蒂厄函数分布的振幅调制胶片。通过胶片紧贴锥镜入瞳面，精确、高效的产生了一簇具有任意类型、任意阶次、任意椭圆参数的马蒂厄光束。理论和实验结果均表明，基于稳相法的“锥镜和振幅调制”产生马蒂厄光束的方法，具有简单、高效、灵活等特点。