多艾里光束合成自聚焦光束的实验实现

多光束合成和单光束聚焦一直是提高激光束功率和功率密度的两个重要方法. 结合艾里光束在自由空间中沿弯曲路径传播的特性, 从数值模拟和实验两个方面, 研究了利用多个一维艾里光束合成自由空间自聚焦光束的方法, 并对所得到的模拟和实验结果进行了对比. 采用分步束传播法, 分别模拟了由四个和八个一维艾里光束合成的自聚焦光束在自由空间中的传播过程, 给出了自聚焦光束在传播过程中横向和纵向的光强分布和变化趋势. 采用计算全息和空间光调制器技术实验, 实现了多个一维艾里光束合成的自聚焦光束. 实验中分别测量了四个和八个一维艾里光束合成的自聚焦光束的横向光强分布. 实验结果和理论结果符合得较好. 另外, 为了进一步增大自聚焦光束的功率, 可以增加参与合成的一维艾里光束的数量. 同时, 自聚焦光束的焦距可以通过调整各个一维艾里光束的相对位置进行调节.     

Airy波包及其自加速效应(续2)

正4艾里光束简单介绍艾里光束,观察艾里光束的加速,并分析自聚焦光束的实验研究.4.1观察艾里光束的加速第一个对艾里光束的观测,最初是由贝里和鲍拉日在1979年预测,这样一个有趣的类波包已在一维和二维结构中实现.实验中,艾里光束表现出在传播中趋于自由加速并保持长距离衍射等特征.1979年贝里和巴拉兹在量子力学的背景下做了一个重要的观测:他们在理论基础上证明了由薛定谔方程描述的自由粒子可以表现出未扩散的艾里     

部分相干Airy光束及其传输的研究

利用高斯-谢尔模型的交叉谱密度公式和惠更斯衍射积分, 得到了部分相干Airy光束的表达式. 对不同相干度的部分相干Airy光束的无衍射和横向加速偏移的性质进行了理论分析并予以实验验证, 结果一致表明部分相干Airy光束也具有无衍射和横向加速度的特性, 而且相干度越低, 部分相干Airy光束的无衍射距离越短, 横向加速度越小. 关键词： 傅里叶光学 全息 部分相干 艾里光束     

可调谐艾里光束及其传输特性

艾里光束是一种新型无衍射光束,解决了激光在传播过程中的衍射效应。基于艾里变换技术,介绍一种可以通过椭圆平顶高斯光束产生的新型艾里光束,即可调谐艾里光束。通过理论计算,可以看出调节椭圆平顶高斯光束的束宽比可获得单尾艾里光束,同时,可调谐艾里光束的尾长可以通过调节入射椭圆平顶高斯光束的阶数来控制。通过研究,当束宽比p=1时,艾里光束的加速方向沿x轴45方向;p=1/2时,加速方向沿x轴31方向,p=1/3时,加速方向为沿x正方向,可见调节束宽比p的大小可以改变艾里光束的加速方向。     

关于Airy光束衍射及自加速性质的研究

对Airy光束的特性做进一步探讨, 一方面对无限宽Airy光束的重心问题给出新的理论说明, 另一方面着重对有限宽情形下的Airy光束的奇特性质进行探讨. 文中采用反证法给出无衍射的讨论, 同时结合数值模拟给出高斯函数及矩形函数限定下的有限宽Airy光束的场分布, 并由此得到其重心位置的轨迹: 重心位置是不变的, 不可能整体自由加速. 最终得到有限宽Airy光束既不可能在自由空间加速, 也不可能是无衍射光束. 关键词： Airy光束 无衍射 自加速 数值模拟     

基于焦散线方法的自加速光束设计

以艾里光束为代表的自加速光束是一类在自由空间中具有弯曲传播特性的新型特殊光束.这类光束因其具有无衍射、自加速和自修复等奇异特性引起了人们的广泛关注,有望应用于光学微粒操控、激光微加工、全光路由和超分辨成像等诸多领域.由于艾里光束只能沿着抛物线的轨迹传播,限制了其在实际应用中的灵活性,因而设计出能够沿着不同轨迹传播的自加速光束是这一研究领域的关键问题,而基于焦散线方法的自加速光束设计是解决该问题的有效途径之一.这一方法是将设计的传播轨迹与光学焦散线联系起来,通过分析形成该焦散线所需的光线簇构造出对应的初始场分布.基于该原理并经过不断发展,不同类型的自加速光束相继得以实现,并且借助维格纳函数还可以同时实现实空间和傅里叶空间的自加速光束设计,为自加速光束的应用提供了更多的可能性.本文对基于焦散线方法的自加速光束设计原理和进展进行全面介绍.     

艾里涡旋光束的多空间维度自由调控

基于多坐标变换技术,依次对一维艾里光束、二维艾里光束以及艾里涡旋光束进行不同坐标系下的变换,实现了艾里光束的两个边瓣方向和嵌入的光学涡旋方向在0到2π范围内的自由调控.分析了边瓣夹角分别为钝角和锐角时的艾里光束以及边瓣垂直时的艾里涡旋光束在传播距离0、2、6、10 cm处的传播动力学特性.理论与实验研究结果表明,通过边...     

可调谐广义艾里光束产生及传播特性

为了调控艾里光束的传播,提出一种广义艾里光束.在传统立方相位基础上引入两个可变旋转角因子θ_1和θ_2,形成新改进的可调谐相位,加载该相位的高斯光束经傅里叶变换后可以产生广义艾里光束.基于衍射突变理论,分析讨论了该光束的双曲抛物线传播行为.重点研究了当旋转角θ_1=π/3和θ_2=7π/6时,该光束在传播距离0、3、6、10cm处的无衍射传播特性;以及旋转因子θ_1=3π/2和θ_2=π/4时,该光束在传播距离0、3、6、10cm处的自愈特性.理论研究表明该光束并非傍轴波动方程的特解,但数值模拟及实验证实其在一定程度上拥有无衍射及自愈特性.该光束不仅可沿任意指定的抛物线轨迹传播,同时还具有与传统艾里光束明显不同的空间强度分布,使其在光学操纵与生物医学等方面有潜在的应用.     

空间诱导产生艾里-贝塞尔光弹研究

利用波动方程,研究了脉冲贝塞尔光束在自由空间传输时的空间诱导群速度色散(SIGVD)效应. 结果表明,三阶SIGVD能使脉冲贝塞尔光束的时域逐渐演化为艾里分布. 由于艾里-贝塞尔光弹是一种新奇的时、空都不扩展的局域波包, 能在光与物质相互作用的很多应用领域发挥作用.因此,本文提出了 通过色散管理技术补偿二阶SIGVD,利用三阶SIGVD在自由空间产生艾里-贝塞尔光弹的方案. 为分析这种光弹的时空传输特性,数值模拟了它在色散介质中的传输情况. 结果表明,这种光弹能在色散介质中保持空域不衍射、时域不色散的稳定传输.     

艾里-厄米-高斯光束在克尔介质中的孤子控制

以非线性薛定谔方程为理论模型,采用分步傅里叶数值模拟方法,讨论了有限能量艾里-厄米-高斯光束在克尔介质中的传输特性以及相互作用。研究表明,通过控制介质的非线性强度和艾里-厄米-高斯光束的初始振幅,可以抑制光束的衍射效应,当它们满足一定条件时,能够产生孤子。通过研究两艾里-厄米-高斯光束的相互作用,发现调整两光束的初始间隔以及相位,可以控制孤子的数量和传输方向。     

Manipulation of Airy Beams in Dynamic Parabolic Potentials

The propagation of finite energy Airy beams in dynamic parabolic potentials, including uniformly moving, accelerating, and oscillating potentials, is investigated. The propagation trajectories of Airy beams are strongly affected by the dynamic potentials, but the periodic inversion of the beam remains invariant. The results may broaden the potential applications of Airy beams, and also enlighten ideas on Airy beam manipulation in nonlinear regimes.     

Electrically switchable finite energy Airy beams generated by a liquid crystal cell with patterned electrode

A pair of electrically switchable finite energy Airy beams is generated by a liquid crystal (LC) cell, where one electrode is patterned by a photomask with a binary-phase pattern. Applying voltage across the LC cell, an index modulation is produced due to the liquid crystal molecules realignment, and the finite energy Airy beams can be generated or erased corresponding to the phase difference between the regions with and without electrode. The diffraction-free and transverse acceleration dynamics of this binary-phase element based finite energy Airy beams were experimentally verified, exhibiting excellent agreement with the theory.     

Accelerating finite energy Airy beams

We investigate the acceleration dynamics of quasi-diffraction-free Airy beams in both one- and two-dimensional configurations. We show that this class of finite energy waves can retain their intensity features over several diffraction lengths. The possibility of other physical realizations involving spatiotemporal Airy wave packets is also considered.     

Specular and vortical Airy beams

A new kind of truncated Airy beams is investigated and discussed. These beams are a superposition of shifted and truncated Airy functions and its specular counterparts, where zeroes or extremal points of the Airy function are chosen as a truncation point. The specular Airy beams are smooth at the truncation point and produce a diffraction pattern similar to Hermite-Gaussian modes. Under propagation in Fresnel zone, specular Airy beams demonstrate a symmetrical acceleration in opposite sides and the beam divergence is proportional to the traveled distance squared. The astigmatic mode converter transforms a two-dimensional specular Airy beam into a quasi-annular field with a nonzero orbital angular momentum. Vortical Airy beams based on truncated Airy functions are also discussed. These beams are similar to Laguerre-Gaussian modes, while their annular structure is changed during propagation.     

Evolution of finite energy Airy beams in cubic-quintic atomic vapor system

In a numerical investigation, we demonstrate the evolution of a one-dimensional and two-dimensional finite energy Airy beam in a Λ-type three-level atomic vapor with linear, cubic, and quintic susceptibilities considered simultaneously with the dressing effect. Quasi-solitons and soliton pairs are observed due to this competition mechanism. We find that the frequency detuning of the pump field and its power greatly affect the formation and evolution of generated solitons. In general, around the two-photon resonance point and for low intensities of the pump field, it is less difficult to form solitons. This investigation enriches the study of the propagation properties of Airy beams and soliton generation in atomic vapor.     

Persistence and breakdown of Airy beams driven by an initial nonlinearity

We study the behavior of Airy beams propagating from a nonlinear medium to a linear medium. We show that an Airy beam initially driven by a self-defocusing nonlinearity experiences anomalous diffraction and can maintain its shape in subsequent propagation, but its intensity pattern and acceleration cannot persist when driven by a self-focusing nonlinearity. The unusual behavior of Airy beams is examined from their energy flow as well as the Brillouin zone spectrum of self-induced chirped photonic lattices.     

Observation of accelerating Airy beams

We report the first observation of Airy optical beams. This intriguing class of wave packets, initially predicted by Berry and Balazs in 1979, has been realized in both one- and two-dimensional configurations. As demonstrated in our experiments, these Airy beams can exhibit unusual features such as the ability to remain diffraction-free over long distances while they tend to freely accelerate during propagation.     

The optical Airy transform and its application in generating and controlling the Airy beam

We propose an optical Airy transform in this paper, and obtain the analytical expressions for the Airy transform of fundamental Gaussian beams and finite energy Airy beams. The setup for performing the optical Airy transform is presented. The Airy transform for Gaussian beams and finite energy Airy beams are theoretically calculated and analyzed. Our results show that the Airy beam can be conveniently generated and controlled through the optical Airy transform of the Gaussian beam. The optical Airy transform also can be used to directly modulate the beam parameters of the incident Airy beam, and it can transform the incident Airy beam into the Gaussian beam.     

Acceleration control of Airy beams with optically induced refractive-index gradient

We demonstrate both experimentally and theoretically controlled acceleration of one- and two-dimensional Airy beams in optically induced refractive-index potentials. Enhancement as well as reduction of beam acceleration are realized by changing the index gradient, while the beam shape is maintained during propagation through the linear optical potential. Our results of active acceleration manipulation in graded media are pertinent to Airy-type beam propagation in various environments.