基于非线性计算全息的非傍轴自加速光束产生与调控

Recently, there has been an increasing interest in Airy beams, i.e., beams whose transverse amplitude dependence at origin is defined by the Airy function. As a new class of non-diffracting self-accelerating beams, Airy beams show superior abilities in generation of curved plasma channels in air, vacuum electron acceleration, and optical micro-manipulation of small particles where the straight light cannot reach. However, Airy beams, mostly generated using linear diffractive elements, are inherently subjected to the paraxial limit. Also, there is a lack of fast and efficient way in controlling Airy beams. .Firstly, this project will focus on generating 1D/2D nonparaxial self-accelerating beams. By employing nonlinear computer-generated-hologram and quasi-phase-matcheing(QPM) technology, the informations of desired reciprocal vector and wavefront are imprinted on a 2D optical superlattice, and the 1D/2D nonparaxial accelerating beams with desired frequency are generated directly without using 3D optical superlattice. The influences of wavelength, intensity, polarization and incident angle of incoming light on the the output beam are studied comprehensively and deeply. Further，the project will study the manipulation of self-accelerating beams theoretically and experimently. The electro-optic effect is introduced to modulate the phase matching of nonlinear optical process in 2D optical superlattice. A wave coupling theory for combined effect of electro-optic effect and other nonlinear optical effect is utilized to determine the optimal direction of external electric field. The influence of external electric field on intensity distribution, caustic and polarization of the self-accelerating beams is examined in detailed. .In summary, the generation and manipulation of 1D/2D nonparaxial self-accelerating beams using nonlinear computer-generated-hologram and QPM nonlinear optical process are studied for the first time, to our best knowledge. The way of obtaining 1D/2D nonparaxial self-accelerating beams of desired frequency based on 2D optical superlattice can break through the paraxial limit and avoid using 3D optical superlattice, and opens up a new possibility for fast and efficient manipulation of self-accelerating beams. In addition, our study is also an important exploration of new physical phenomena and applications of 2D optical superlattice.

作为一类新型无衍射光束，Airy光束奇特的横向自加速性质使得它在弯曲等离子体通道、光学微操控、电子加速等方面有重要应用。然而，傍轴限制、波长单一和不易操控等问题制约其进一步发展。本项目以非线性计算全息术为基础，将光束波前和倒格矢信息“印刻”到二维光学超晶格上，利用二维光学超晶格中准相位匹配非线性光学效应，直接产生所需波长的一维和二维非傍轴自加速光束，并揭示光束焦散和加速特性对入射光光强、偏振态和入射角等因素的依赖关系。项目进一步研究非傍轴自加速光束的电光调控，利用电光效应改变介质折射率或相互作用光的偏振态，进而调整非线性光学效应的准相位匹配过程，最终达到调控非傍轴自加速光束焦散、传播轨迹和偏振态等性质的目的。电光调控方便灵活，响应速度可达亚纳秒。本项目首次利用非线性计算全息术获得新波长、可电控的非傍轴自加速光束，完善了自加速光束研究体系，为探索光学超晶格新物理效应与新应用提供一个重要思路。

自加速光束在弯曲等离子体通道、光学微操控、电子加速等方面有重要应用，但是傍轴限制、波长单一和缺乏主动调控方式限制了其应用范围，因此，研究自加速光束的非线性方法产生与调控具有重要意义。本项目的主要研究两个方面内容：1）利用非线性计算全息方法，研究非傍轴自加速光束的非线性光学方法产生与传播特性；2）研究了非傍轴自加速光束的电光调控。通过3年的项目实施，我们得到了以下学术成果：1）通过研究非傍轴自加速光束的波前特征及其傅里叶谱，利用非线性计算全息方法，得到了产生倍频非傍轴自加速光束的二维光学超晶格极化图案；2）提出一种全新的极化编码方案，其极化占空比不为0.5，用此方案极化的二维光学超晶格不但可以产生倍频非傍轴自加速光束，还可以引入电光调控，实现非傍轴自加速光束的快速调控；3）研究了二维圆对称自加速光束在非线性晶体中的传输演化行为，分析了各向异性对传输特性的影响，得到一种利用单轴晶体产生涡旋自加速光束的方法；4）在单轴晶体中引入电光效应，研究了二维圆对称自加速光束的电光耦合情况，得到了一种控制自加速光束光场分布、相位分布、偏振分布、自旋-轨道角动量转换的调控方法；5）为了改善传统自加速光束的性能，我们对自加速光束的傅里叶谱进行低通、带通、高通滤波等处理，从而实现对光束光强分布的调制，得到性能优越可控的 “光学针”，可望在医学治疗方面有重要应用；6）得到了直接产生主瓣尺寸更小、能量更强的super-Airy光束激光器设计方案，使得装置小型化。本项目的实施解决了传统自加速光束的傍轴限制、波长单一和不易控制等问题，为探索光学超晶格的新物理效应和新应用提供一个重要思路。我们总结了研究成果，在Optics Express、Applied Opitcs和Optics Communications等主流刊物上发表9篇SCI或EI收录的学术论文，发表专利3项，参加学术会议4次，培养和协助培养了3名硕士研究生。