应用变换光学理论调控电磁场光束束宽

根据变换光学理论,提出了利用超常材料调控光束束宽及将有限束宽光束变成线光束的理论方案,得到了所需超常材料的介电常数和磁导率的解析结果。应用这些结果,可以实现对光束束宽的调控或者将有限束宽光束压缩成线光束。利用有限元分析方法进行全波仿真,仿真结果与理论相符合,可应用于压缩或扩展电磁波束的能量密度。线光束中心处的场能量密度极大,可应用于增强非线性光学效应等方面。     

高斯光束非线性“热像”效应研究

高功率激光系统中非线性“热像”强度可能达到光学元件损伤阀值，从而对系统的安全运行造成威胁.以往的非线性“热像”现象研究都是基于无限大平面光波背景，但实际系统中传输的是有限束宽光束.本文以高斯光束为例，基于无像差自聚焦理论分析了有限束宽光束的“热像”形成规律.结果表明，高斯光束“热像”的强度与位置在光束腰斑较小时与平面光波情况有明显不同，但光束腰斑较衍射物大得多时，高斯光束可以近似当作平面光波处理.     

强非局域介质中高斯型损耗空间光孤子

 利用变分法研究了1+1维傍轴高斯光束在含有小损耗的强非局域非线性介质中的传输特性，得到了光束各参量的演化方程、束宽的演化规律和一个临界功率。在介质损耗足够小的前提下，当光束初始功率等于临界功率时，得到了一个束宽随传输距离缓慢展宽的准空间光孤子——损耗空间光孤子；当光束初始功率小于临界功率时，光束束宽则按雅可比椭圆正弦函数和椭圆余弦函数作准周期展宽变化；当光束初始功率大于临界功率时，光束束宽将从按雅可比椭圆正弦函数和椭圆余弦函数作准周期压缩变化过渡到按雅可比椭圆正弦函数和椭圆余弦函数准周期展宽变化。     

激光二极管光束在各向异性非柯氏大气湍流中的传输质量

以厄米-高斯混合模形式描述激光二极管光束的分布,利用光束二阶项矩阵进行计算,研究了光束束宽与光束传输因子之间的关系,并对各向异性大气湍流中广义指数和各向异性系数对光束传输因子的影响进行了分析。结果表明,对于不同的湍流强度,均存在不同的束宽使得光束传输因子最小。此外,大气湍流模型中各向异性系数的增大使得大气湍流对光束传输因子的影响相应减小。通过二维光束质量轨迹图的仿真,证实了各向异性系数对光束传输因子轨迹的影响将随着传输距离的增大变得更加明显。所得结果将有利于大气光传输理论的发展,并对大气光通信、激光雷达探测等应用有着重要意义。     

有限宽光束在生物组织中传输的蒙特卡罗方法

基于光在生物组织中的传输理论,研究有限宽光束在生物组织中的传输特性.利用入射光强与格林函数进行卷积计算,推导了有限宽光束在圆柱坐标系下的光传输过程,给出了有限宽光束的光传输方程.以高斯光源和平圆光源为例,进一步给出了两种光源的有限宽光束在生物组织中的光传输方程.介绍了Monte Carlo方法原理及模拟光在多层生物组织中的传输过程.给出了典型三层生物组织的散射系数、吸收系数和折射率等光学参数.利用Monte Carlo方法模拟了有限宽光束在三层生物组织中的传输特性,对比研究了高斯光源和平圆光源有限宽光束在三层生物组织传输时光学参数漫透射率、漫反射率和光能流率的变化规律.这些参数的变化规律可为光在生物组织传输的实际应用提供理论指导.     

湍流大气中斜程传输部分相干光的光束扩展

运用维格纳分布函数与广义惠更斯菲涅耳原理,推导出部分相干光束在任意折射率起伏功率谱模型的大气湍流中斜程传输时,其束宽传输的一般解析表达式。在此基础上,以部分相干平顶(PCFT)光束为例,给出了PCFT光束在大气湍流中斜程传输的束宽扩展解析表达式。在合肥地区大气折射率结构常数高度分布模式下开展了数值计算和分析,并与水平传输时的结果进行了比较。研究结果表明,光束在斜程传输时的束宽不仅与光束阶数、空间相干度、束腰半径、湍流的强弱和传输距离有关,还与天顶角密切相关。光束的阶数越高,空间相干性越差,天顶角越小,则其束宽扩展受湍流的影响就越小。当天顶角小于60°时,大气湍流对斜程传输光束束宽的影响明显小于水平传输的情况。     

梯度负折射率介质中高斯光束传输特性的研究

导出了高斯光束在梯度负折射率介质中的ABCD矩阵,据此得到光束在此介质中的传输模型.并利用此模型分析了高斯光束在梯度负折射率介质中的传输特性,发现它能产生空间孤子及呼吸子形式的传输,并发现光束的束腰半径不一定是最小束宽半径.还研究了梯度系数对介质聚焦能力的影响,据此可以设计出相应聚焦能力所需要的折射率分布.最后分析了传输时高斯光束曲率半径的变化情况,与光束束宽半径的变化显著不同,曲率半径始终从无穷大开始,然后产生一个个周期性的变换.     

强非局域克尔介质中光束传输的变分问题

在非局域克尔介质中,光束的演化规律服从非局域非线性薛定谔方程。用变分法对此问题进行了重新表述。在强非局域的情况下,通过对介质响应函数进行泰勒展开,可以解析地表示变分问题。束宽的演化规律也可以定性地从光束束宽变分势得出。运用瑞利-里兹方法求解其变分方程,分别求出光束在自散焦和自聚焦介质中的变分解。对于自聚焦介质,当输入功率为某一特定值时,可以得到空间孤子,其束宽在传输过程中保持不变。通过与其他方法得到的解比较表明,变分法是解析讨论光束在非局域非线性介质中演化规律的方法之一。     

强非局域克尔介质中光束传输的变分问题

 在非局域克尔介质中,光束的演化规律服从非局域非线性薛定谔方程。用变分法对此问题进行了重新表述。在强非局域的情况下,通过对介质响应函数进行泰勒展开,可以解析地表示变分问题。束宽的演化规律也可以定性地从光束束宽变分势得出。运用瑞利-里兹方法求解其变分方程,分别求出光束在自散焦和自聚焦介质中的变分解。对于自聚焦介质,当输入功率为某一特定值时,可以得到空间孤子,其束宽在传输过程中保持不变。通过与其他方法得到的解比较表明,变分法是解析讨论光束在非局域非线性介质中演化规律的方法之一。     

偏离束腰入射对非局域非线性介质中高斯光束演化的影响

从1+1维强非局域模型出发，讨论了偏离束腰入射的高斯光束在非局域非线性介质中的传输 特性，得到了精确的解析解.结果表明，在聚焦介质中偏离束腰入射时，不论入射功率多大 ，光束束宽将发生周期性波动，光孤子不复存在，这与从高斯光束束腰入射的情况有本质的 不同；入射功率决定了光束平均束宽的大小，入射位置决定了光束初始的演化趋势.比较了在入射位置相同的条件下，聚焦介质、散焦介质和线性均匀介质中光束的演化.给出了“空 间啁啾”的定义，偏离束腰入射的物理本质是光束的不同入射位置对应不同的初始空间啁啾 .空间啁啾的概念， 关键词： 非局域非线性介质 空间光孤子 高斯光束     

基于电磁超材料的两种等效参数提取算法的比较分析

基于传统反演算法和Kramers-Kronig关系改进算法, 分别提取弱耦合和强耦合超材料渔网结构模型的等效参数, 并对两种算法的有效性及普适性进行了探讨.理论分析及计算结果表明, 传统的反演算法可以准确地反演弱、强耦合情形下电磁超材料结构的等效参数, 但计算复杂度较高;而基于Kramers-Kronig关系的改进算法巧妙地降低了计算的复杂度, 能简单准确地提取弱耦合情形下电磁超材料结构的等效参数, 但对于强耦合情形则不适用, 原因在于强耦合情形破坏了Kramers-Kronig关系的解析且连续性要求. 研究结果拓展了等效媒质理论并可为新的电磁超材料的设计提供理论参考. 关键词： 超材料 反演算法 Kramers-Kronig关系 等效参数     

Metamaterials and metasurfaces for designing metadevices:Perfect absorbers and microstrip patch antennas

In the past twenty years, electromagnetic metamaterials represented by left-handed metamaterials(LHMs) have attracted considerable attention due to the unique properties such as negative refraction, perfect lens, and electromagnetic cloaks. In this paper, we present a comprehensive review of our group's work on metamaterials and metasurfaces. We present several types of LHMs and chiral metamaterials. As a two-dimensional equivalent of bulk three-dimensional metamaterials, metasurfaces have led to a myriad of devices due to the advantages of lower profile, lower losses, and simpler to fabricate than bulk three-dimensional metamaterials. We demonstrate the novel microwave metadevices based on metamaterials and metasurfaces: perfect absorbers and microwave patch antennas, including novel transmission line antennas,high gain resonant cavity antennas, wide scanning phased array antennas, and circularly polarized antennas.     

左手材料微结构构型的传输线比拟模型

提出了基于传输线比拟模型的左手材料微结构设计方法,并对此进行了分析、验证.首先根据已有的具有左右手性质的基本传输线模型,通过类比构建了具有左手性质的新模型,进而通过定性分析传输线网络中的各元件与微结构连续介质构型的形状及尺寸的对应关系,推断出模型中各部分的具体尺寸,从而得到了一个合理的左手材料微结构构型及其对应的传输线比拟模型.对设计的模型进行了实验测试,验证了模型确实具有左手性质.最后,通过数值模拟和实验,研究了微结构的各个尺寸参数对材料出现左手性质的带宽和频段的影响,确定了微结构中对左手性质影响最大的尺寸参数.     

基于传输线的特异材料

特异材料(metamaterials)是指自然界中不存在的具有奇异电磁特性的人工结构,通常指的是介电常数和磁导率同时为负值的左手材料(left\\|handed materials).自从2002年利用传输线制备左手材料的思想被提出后,人们对基于传输线的特异材料进行了大量的研究.文章着重概述了近年来人们所提出的几种典型的传输线特异材料的结构、制备方法、实现左手性的原理以及各自的特点.     

Distribution regimes of intense laser beam in a self-consistent plasma channel

In the present work, we investigate the distributed regimes of an intense laser beam in a self-consistent plasma channel. As the intensity of the laser beam increases, the relativistic mass effect as well as the ponderomotive expulsion of electrons modifies the dielectric function of the medium due to which the medium exhibits nonlinearity. Based on Wentzel–Kramers–Brillouin and paraxial ray theory, the steady-state solution of an intense, Gaussian electromagnetic beam is studied. A differential equation of the beamwidth parameter with the distance of propagation is derived, including the effects of relativistic self-focusing (SF) and ponderomotive self-channeling. The nature of propagation and radial dynamics of the beam in plasma depend on the power, width of the beam, and Ω _p, the ratio of plasma to wave frequency. For a given value of Ω _p (<1), the distribution regimes have been obtained in beampower–beamwidth plane, characterizing the regimes of propagation as steady divergence, oscillatory divergence, and SF. The related focusing parameters are optimized introducing plasma density ramp function, and spot size of the laser beam is analyzed for inhomogeneous plasma. This results in overcoming the diffraction and guiding the laser beam over long distance. Numerical computations are performed for typical parameters of relativistic laser–plasma interaction studies.     

Huge Casimir effect at finite temperature in electromagnetic Rindler space

We investigate the Casimir effect at a finite temperature in the electromagnetic Rindler space, and we find that the Casimir energy is proportional to T(4)/d(2) in the high-temperature limit, where T ≈ 27 °C is the temperature and d ≈ 100 nm is a small cutoff. We propose to make metamaterials to mimic the Rindler space and measure the predicted Casimir effect. Because the parameters of metamaterials we proposed are quite simple, this experiment would be easily implemented in the laboratory.     

Beamwidths of a diffracted laser using four proposed methods

The International Organization for Standardization has been preparing test methods for laser beamwidth and propagation factors. Several techniques have been proposed. The purpose of this paper is to compare the results of applying the various proposed definitions and measurement methods to the same diffracted beam. A heavily apertured laser beam is passed through a focusing lens; the beamwidth is measured at several locations on each side of the focus. The apparent beamwidth is calculated using the diameter that passes 86.5% of the light, the knife edge, the slit and the second moment methods of beamwidth measurement.An Invited Paper     

Screw split ring resonator as building block of three-dimensional chiral metamaterials

We proposed and numerically investigated the influence of spatial topology on the infrared frequency region response of chiral metamaterials based on discrete deformed split ring resonators. Compared with the well studied continuous helix, the proposed metamaterials with discrete topology exhibit broad band chiral electromagnetic response. It is shown that the conversion between left and right circular polarization waves for our model is much broader than the continuous helix model. The observed cross-coupling between electric and magnetic fields results from the chiral electric currents on the resonators due to the broken mirror symmetry. The findings are useful for the design of future real three-dimensional chiral metamaterials with tunable optical response.     

Arbitrary angle waveguide bends based on zero-index metamaterials

In this paper, efficient arbitrary angle bends based on impedance-matched zero-index metamaterials (ZIMs) are proposed. Numerical simulations on ZIM-based bends are carried out in waveguide systems. The results show clearly that electromagnetic waves can tunnel through the ZIM-based bends with high transmittance at any bending angles. Moreover, a realistic ZIM-based bends are designed and fabricated on microstrip transmission line. Both simulated and experimental results confirm well the low loss and arbitrary angle bending effects in a system hiring ZIM-based microstrip ring resonator as bending corners.