可控空心光束在单轴晶体中的传输特性

基于光束在各向异性单轴介质中的傍轴矢量传输理论,对可控空心光束(CDHB)在单轴晶体中的传输特性作了研究.得出该光束在单轴晶体中传输的横向慢变振幅的表达式,并利用此表达式作数值计算,研究了CDHB在单轴晶体中的传输特性.研究表明,可控空心光束在单轴晶体中传输时,控制参数ξ和光束阶数N的取值对其光强分布有较大的影响.随着...     

单轴晶体中光轴任意取向时寻常光与非常光间的离散

晶体器件（特别是非线性光学器件）的性能与晶体内o光与e光的离散有很大的关系。详细讨论了光在晶体表面折射时，对于任意光轴取向、任意入射角情况，如何确定o光与e光的离散。借助于转动晶体的方法，形象地描绘出e光相对o光的离散曲线。当入射角较大时，离散曲线的形状 随光轴取向变化很大：从简单的圆或椭圆到复杂的双闭合曲线。理论计算与实验结果很好地吻合。     

Effect of Critical Beam Radius on Self-focusing of cosh-Gaussian Laser Beams in Collisionless Magnetized Plasma

Effect of critical beam radius on self-focusing of cosh-Gaussian laser beams in collisionless magnetized plasma under ponderomotive nonlinearity forms the main core of present work. To investigate propagation dynamics of cosh-Gaussian laser beams in collisionless magnetized plasma, well established parabolic equation approach under WKB and paraxial approximations is employed. Our study is crucially pivoted on the concept of critical curve and subsequent determination of numerical interval for decentered parameter to sustain the competition between diffraction and self-focusing during the propagation of laser beam. Additionally, in the present study an interesting feature in the self-focusing region of the critical curve has been attempted for different values of decentered parameter.     

费米气体在光晶格中的自俘获现象及其周期调制

研究了一维光晶格中费米气体从BCS区过渡到unitarity区研究相图及周期调制现象. 通过调节散射长度与耠合系数对相图的影响, 发现在unitarity 区, 从约瑟夫振荡到振荡自俘获及振荡自俘获到自俘获, 存在耦合系数的临界值, 同时得到了临界耦合系数与散射长度的关系. 关键词： 费米气体 自俘获 周期调制     

Self-trapping light waves and quanta: Towards an explanation of wave-photon duality

Advances in laser technology have made it possible to discover the light-trapping effect and on the basis of its theory to build up a classical understanding of quantum energy, structure of light.Three unanswered questions are discussed: Why is the amount of quantum energy,E, proportional to the wave frequency? Why does E not depend on the wave intensity? Why is Planck's constant h valid for waves and particles of various kinds? The answer lies, in the case of photons, in the non-linearity of the classical Maxwell equations, which lead to the non-linear wave equation, and which in turn yield the light self-trapping effect. The model based on the non-linearity of Maxwell's equations and self-trapping quantitatively fits Planck's constant and provides answers to the above questions.     

Self-trapping and Macroscopic Tunnelling of Superfluid Fermi Gases in Multi-well Potentials

We study the tunnelling dynamics of superfluid Fermi gases trapped in multi-well system along the BEC-BCS crossover. Within the hydrodynamical model and by using the multi-mode approximation, the self-trapping dynamics of superfluid Fermi gases in multi-well system are obtained numerically. We find that the self-trapping to diffusion transition strongly depends on the well number. When the well number is less than three, the self-trapped state takes place easier on the BEC side than that on the BCS side. However, when the well number is larger than three, the self-trapped state takes place easier on the BCS side instead of the BEC side. Furthermore, by considering a superfluid of 40K atoms, we obtain the zero-mode and π-mode Josephson frequencies of coherent atomic oscillations in double-well system. It is noteworthy that the Josephson mode, especially, the existence of π-mode frequency strongly depends on the atoms number on the BCS side.     

双势阱玻色-爱因斯坦凝聚体系的自俘获现象及其周期调制效应

研究了双势阱玻色-爱因斯坦凝聚体系(BEC)的自俘获现象(self-trapping). 在平均场近似下通过相平面(phase space)分析的方法研究了两种自俘获的机理：1)势阱中的粒子数在平衡位置附近振动，而相对相位随时间单调变化(running-phase); 2) 势阱中的粒子数和相对相位都在平衡点附近振动. 研究了周期调制场对自俘获现象的影响，发现发生自俘获现象的相变参数能够被周期场非常有效的调制，从而在弱相互作用BEC体系中也可以观察到自俘获现象. 还研究了多体量子涨落对自俘获现象的影响，讨论了在现有的实验条件下对凝聚体自俘获现象进行观察和周期调制. 关键词： 玻色-爱因斯坦凝聚 自俘获 双势阱 周期调制     

超短超强激光在稀薄等离子体中的自聚焦传输

开展超短超强激光与次稠密等离子体相互作用实验,采用探针光对激光等离子体相互作用区域进行阴影成像,研究了不同激光功率与临界功率比值及不同激光脉冲长度与等离子体波波长比值下的激光在次稠密等离子体中的自聚焦传输。结果表明:相对论效应是超短脉冲在次稠密等离子体中的主要自聚焦机制,激光功率与临界功率比值是影响超短脉冲在次稠密等离子体中形成自聚焦的关键条件。     

半导体光折变介质中光束传输的自囚禁及周期调制

推导了光束在半导体光折变介质的光子晶格中演化的二能级形式, 给出了光束在其中传播时二能级方程的经典正则形式. 解析计算出了经典正则方程的不动点并对其稳定性作了分析, 计算出了拓扑结构变化的临界值. 根据二能级方程的经典正则形式做出了空间相图, 进一步分析了半导体光折变介质中光束传输的自囚禁现象, 发现有两种形式的自囚禁: 1)能级中的布居数差和相对相位都在平衡点附近振动; 2)能级中的布居数差在平衡点附近振动, 而相对相位单调变化. 分别从高频、低频、中频三个方面研究了外加周期调制对自囚禁的影响, 发现在高频调制中发生自囚禁现象的相变参数能够被周期场非常有效的调制, 使得光束在半导体光折变介质中传输时, 在非线性效应影响较小时也能够发生自囚禁. 关键词： 半导体光折变介质 自囚禁 二能级形式 周期调制     

大芯径石英光纤中皮秒脉冲激光的自聚焦

本文报道了对大芯径石英光纤中皮秒脉冲激光自聚焦现象的实验研究和理论分析.文中测量了自聚焦先场的近场光强轮廓,研究了自聚焦光场的时域和频域性质,并对环形自聚焦光场的成因进行了解释.     

强激光圆对称超高斯光束的自聚焦环

 通过数值求解非线性薛定谔方程,详细描述了圆对称超高斯光束在Nd:glass介质中传输形成的自聚焦环。初始光束受到扰动后,环就会分裂形成强烈的细光束,显示出自聚焦环的不稳定性,细光束具有很大的峰值光强,将对介质造成极大的危害。     

溶胶Cds毫微晶的自聚焦和自位相调制

本文首次报道了氩离子激光在溶胶CdS半导体毫微晶中产生的自聚焦、热自散焦及自位相调制,实验测得此种材料具有很大的克尔(Kerr)非线性系数n_2,比CS_2大10~5倍。并且,文中还分析了这种具有弱吸收的半导体溶胶毫微晶的非线性自位相调制机理及其与热自位相调制的差别。     

Self-trapping and Macroscopic Tunnelling of Superfluid Fermi Gases in Multi-well Potentials

We study the tunnelling dynamics of superfluid Fermi gases trapped in multi-well system along the BEC-BCS crossover. Within the hydrodynamical model and by using the multi-mode approximation, the self-trapping dynamics of superfluid Fermi gases in multi-well system are obtained numerically. We find that the self-trapping to diffusion transition strongly depends on the well number. When the well number is less than three, the self-trapped state takes place easier on the BEC side than that on the BCS side. However, when the well number is larger than three, the self-trapped state takes place easier on the BCS side instead of the BEC side. Furthermore, by considering a superfluid of ⁴⁰K atoms, we obtain the zero-mode and π-mode Josephson frequencies of coherent atomic oscillations in double-well system. It is noteworthy that the Josephson mode, especially, the existence of π-mode frequency strongly depends on the atoms number on the BCS side.     

无线电窄波束在低电离层中的聚焦和散焦

推导了无线电窄波束在电离层中传输的非线性几何光学方程,分析了无线电窄波束在低电离层中传输的聚焦和散焦原理,推导出了散焦参数和聚焦参数的计算公式,研究了无线电窄波束在低电离层中传输的散焦现象,讨论了电波频率和功率对发散波束宽度的影响。计算结果表明：低电离层主要表现为一种散焦介质,使电波波束发散,当电波频率较低并且功率较大时,波束散焦现象非常明显,使到达目标点的功率密度大幅度降低,而当频率达到数GHz时,波束散焦现象很微弱。     

HMO in nonlinear optics

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Dynamics of resonant self-focusing on second harmonic generation of Gaussian laser beam in a rippled density plasma

Resonant second harmonic generation by a Gaussian laser beam in a rippled density plasma is studied using the moment theory approach. The nonlinearity arises through the relativistic mass effect and ponderomotive forces. The laser beam creates a plasma channel and gives rise to electron density perturbation at the laser frequency. The density perturbation beats with electron quiver velocity to produce second harmonics. The ripple provides phase matching and makes the process a resonant one. The second harmonic power efficiency is increased effectively with density ripple. Self-focusing causes enhancement in the efficiency of harmonic generation.     

激光自聚焦和成丝模拟中的并行计算方法

已编制完成三维非线性流体力学与激光传播耦合并行模拟程序,用以研究高强度激光在稀疏等离子体中的自聚焦和成丝不稳定性形成机制.介绍该三维并行程序中所使用的数值方法和并行算法.     

强激光圆对称超高斯光束的自聚焦环

通过数值求解非线性薛定谔方程 ,详细描述了圆对称超高斯光束在 Nd:glass介质中传输形成的自聚焦环。初始光束受到扰动后 ,环就会分裂形成强烈的细光束 ,显示出自聚焦环的不稳定性 ,细光束具有很大的峰值光强 ,将对介质造成极大的危害     

单轴晶体中的负折射现象研究

分析了在各向同性介质和单轴晶体界面实现负折射的最佳条件。计算发现,通过调节光轴角和各向异性参量可以使得负折射现象更为明显,获得最佳光轴角和最大入射临界角。各向异性强的晶体实现负折射的入射角范围可能会很大。讨论了单轴晶体中和负折射率介质中的负折射现象的区别：负折射率介质中的负折射是由负的折射率引起的,单轴晶体中是由于各向异性决定的。同时还发现单轴晶体中的能流负折射现象不能实现Pendry在理论上所预言的完美透镜。