Acousto-optic interaction of diverging Gaussian beams in anisotropic media

A strong acousto-optic interaction of bounded light and sound beams of a Gaussian shape is considered for different geometries permitting long-term interaction. The anisotropic spreading of an acoustic beam in the course of its propagation is taken into account. The spectra of light beams are described by a Gaussian-polynomial expression, and a set of differential equations is derived which allows one to describe various geometries of acousto-optic diffraction. It is demonstrated that the transmission function of an acousto-optic cell essentially depends on the ratio between the dimensions of the light and sound beams and on the angle between the propagation direction of the diffracted beam and that of the incident beam. The degree of spreading of the acoustic beam noticeably affects the suppression of the transmission side lobes.     

Multiple filamentation of terawatt laser pulses in air

The filamentation of femtosecond light pulses in air is numerically and experimentally investigated for beam powers reaching several TW. Beam propagation is shown to be driven by the interplay between intense, robust spikes created by the defects of the input beam and random nucleation of light cells. Evolution of the filament patterns can be qualitatively reproduced by an averaged-in-time (2D+1)-dimensional model derived from the propagation equations for ultrashort pulses.     

非傍轴矢量高斯光束的传输

运用非傍轴光束传输的矢量矩理论，对非傍轴矢量高斯光束的传输特性进行了系统的研究.结果表明，基于二阶矩定义的横向光束宽度在光束传播过程中满足简单的双曲线变化规律，并且给出了光束传输因子的解析表达式.就高度非傍轴情形，进一步给出了简洁的计算公式，在高斯光源线度趋向零的极限情形下，横向的最大发散角为90°.同时，还推广到了傍轴情形，得到了与原有傍轴公式稍有区别的结果，而且光束传输因子始终保持略大于1最后，对非傍轴矢量高斯光束和非傍轴标量高斯光束的传输进行了比较，结果显示对于线度在两个波长范围之内的高斯光源发散 关键词： 矢量高斯光束 光束传输 非傍轴 二阶矩     

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...     

All Optical Light Deflection and Displacement Using Nonlinear Slab Waveguide

The possibility of all optical control of light deflection and displacement through a planar nonlinear waveguide has been discussed in this article. In this scheme a strong command beam controls the propagation characteristics of a weak signal beam in a nonlinear waveguide. Employing variational approach, we have established a set of coupled nonlinear equations for the displacement of the center of gravity, beam size, deflection angle, and beam divergence of the signal beam. These equations have been solved numerically to confirm the possibility of all optical control of deflection and displacement of a signal beam by a command beam.     

铷蒸气激光器3D理论模型的建立及阈值特性模拟

基于三能级速率方程理论,结合惠更斯-菲涅尔衍射积分公式,利用分步光束传播方法建立了半导体泵浦碱金属蒸气激光器(DPAL)端面泵浦3D理论计算模型,用于模拟研究铷蒸气激光器的泵浦阈值特性。该模型将光束传播、光与物质相互作用独立考虑,利用迭代算法求解。考虑激光器腔内模式与泵浦光模式匹配对阈值特性的影响,模拟了单端泵浦铷蒸气激光器内部的三维动力学过程。在具体算例中研究了模式匹配最佳时,在阈值工作状态下铷蒸气室中的三维粒子数分布,以及沿不同轴线的增益分布。仿真了在最佳模式匹配位置附近,泵浦光模式变化对阈值特性的影响。根据蒸气池中粒子数分布和光场分布具体分析了模式匹配影响阈值特性的机理。同时还模拟了不同长度蒸气池对阈值特性的影响。结果表明,腔参数与泵浦光模式之间存在一定的关系,对于特定的泵浦光模式,存在恰当的腔参数,使得阈值达到最小。     

铷蒸气激光器3D理论模型的建立及阈值特性模拟

基于三能级速率方程理论,结合惠更斯-菲涅尔衍射积分公式,利用分步光束传播方法建立了半导体泵浦碱金属蒸气激光器(DPAL)端面泵浦3D理论计算模型,用于模拟研究铷蒸气激光器的泵浦阈值特性。该模型将光束传播、光与物质相互作用独立考虑,利用迭代算法求解。考虑激光器腔内模式与泵浦光模式匹配对阈值特性的影响,模拟了单端泵浦铷蒸气激光器内部的三维动力学过程。在具体算例中研究了模式匹配最佳时,在阈值工作状态下铷蒸气室中的三维粒子数分布,以及沿不同轴线的增益分布。仿真了在最佳模式匹配位置附近,泵浦光模式变化对阈值特性的影响。根据蒸气池中粒子数分布和光场分布具体分析了模式匹配影响阈值特性的机理。同时还模拟了不同长度蒸气池对阈值特性的影响。结果表明,腔参数与泵浦光模式之间存在一定的关系,对于特定的泵浦光模式,存在恰当的腔参数,使得阈值达到最小。     

Nonlinear diffraction in a system of quantum dots

We consider the problem of propagation of large-intensity monochromatic radiation in a solid with the three-dimensional superlattice of quantum dots interlinked by strong tunneling along one axis. Electrons are treated in a classical way in the formalism of the Boltzmann kinetic equation for the distribution function. Analysis of the Maxwell equations for this case yields a (2+1)-dimensional equation, which has a form similar to the Schrödinger nonlinear equation. Various regimes of the electromagnetic-field propagation were numerically analyzed. The super-Gaussian light beam was found to undergo a waist stage, and the interaction of light beams led to their merging.     

Broad band resonant light pressure

This paper treats the mechanical pressure of resonant light acting on a two-level system, where the degenerate magnetic sublevels are taken into account. The theory is developed with arbitrary relations between the quantization axis and the propagation and polarization of the light. Rate terms are obtained both for spontaneous and induced transitions; the requirements of incoherence put restrictions on the possible geometries of the experiment. The rate equations are restricted to motion along a light beam only; this one-dimensional case is simpler to handle. For small recoil velocities a Fokker-Planck equation is derived, and an adiabatic elimination procedure enables us to derive an equation for the velocity distribution of the total population. The assumptions and approximations are formulated and discussed.     

Beam Propagation Factor and Generation of Cosh-squared-Gaussian Beams

A new light beam termed as a cosh-squared-Gaussian beam (ChSGB) which may be one of solutions of the paraxial wave equation for propagation in complex optical systems has been introduced. Their beam propagation factor (M2-factor) is derived and schemes to generate this light beams are proposed.     

Beam Propagation Factor and Generation of Cosh-squared-Gaussian Beams

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Instability of a light beam and its decomposition with thermal self-stress in a moving medium

On the basis of linearized equations for perturbations in a one-dimensional light beam propagating in a moving medium with thermal nonlinearity, the article shows the possibility of an exponential growth of these perturbations with an intensity above the critical in the beam. Numerical solutions were carried out for the nonlinear equations of the propagation of Gaussian beams, showing that small perturbations can lead to decomposition of the beams.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 21, No. 11, pp. 1610–1617, November, 1978.     

Towards observation of sub-diffractive pulse propagation in photonic crystals

It is shown that sub-diffractive (self-collimating) propagation of ultrashort pulses of narrow light beams is possible in two dimensional planar photonic crystal slabs (in particular made with air holes in Si₃N₄ slab) where the sub-diffractive propagation of monochromatic beam of visible light has been demonstrated previously both theoretically and numerically. We found that the sub-diffractive propagations of the pulses of duration of more than 40 fs are indistinguishable from that of monochromatic beams. However, for the pulses with duration less than 40 fs their propagation peculiarities associated with asymmetric spatiotemporal misshaping, spatial and temporal broadening come into play. The effects are pronounced for the pulses of duration less than 20 fs. The phenomena are shown for both TM and TE polarized light by means of numerical integration of 2D Maxwell’s equations with finite-difference time-domain technique.     

聚焦部分相干涡旋光束的焦移

基于部分相干光的传输理论获得了部分相干涡旋光束被光阑透镜聚焦后的传输方程。基于这些方程研究了部分相干涡旋光束的焦移现象。研究结果表明,部分相干涡旋光束的焦移不仅依赖于菲涅耳数,而且依赖于光束的相干长度和涡旋光束的拓扑荷数。菲涅耳数越小,焦移量越大;部分相干涡旋光束的相干长度越小,焦移量越大;涡旋光束的拓扑荷数越大,焦移量越大。     

光纤端面衍射场光束参数及其测量

基于非傍轴标量光束的传播理论和横截面上光强的精确描述,分析了光纤端面衍射场光束特征参数的解析表达式,并与傍轴近似条件下的结论进行了比较.证明了傍轴近似对于弱导光纤的合理性,但是随着光纤相对折射率差Δ增大,傍轴近似由于忽略了衍射角度,远场发散角角半径和M2因子比考虑衍射角度时偏小.最后提出了一种可行的实验测量光束参数的方法,这种方法没有忽略衍射角度影响,从理论上说,比傍轴近似更为客观可靠.     

矢量效应对超短脉冲光束非傍轴传输的影响

从严格的矢量非傍轴传输方程出发,并通过傅里叶变换及角谱分析的方法,分析了在超短脉冲光束中,矢量效应对其在自由空间中的非傍轴传输的影响。结果表明,矢量效直对脉冲光束的标量傍轴解的修正有着重要的影响,当对脉冲光束进行非傍轴传输处理时,必须考虑它的矢量特性。基于上述分析,得到了支配超短脉冲光束传输的矢量非傍轴方程的一个完整积分解。从这个积分解出发,通过对电场进行泰勒级数展开的方法,得到了一种相对简单的方法,通过这种方法,可以从脉冲光束的已知标量傍轴解来求出矢量非傍轴波动方程的相对精确解。     

Comparison of two approximate methods for hard-edged diffracted flat-topped light beams

The integral resulted in an infinite series of Bessel functions and expanding a hard aperture into a complex-Gaussians shape are proposed as two methods for studying the propagation properties of the hard-edged diffraction flat-topped light beam. Using the two methods, the corresponding analytical propagation equations of flat-topped light beams through a circular apertured ABCD optical system are obtained. Some numerical calculations and comparative analyses by using the two methods and the diffraction integral formulae are made. It is shown that the first method of an infinite series of Bessel functions is superior to the second of expanding a hard aperture function into a complex-Gaussians shape at the aspect of calculation accuracy, but the second method is superior to the first method at the aspect of the improvement in the calculation efficiency.     

LD泵浦的Nd:YVO_4激光器被动式产生近似无衍射绿光

使用连续式输出的砷化镓半导体激光器泵浦的掺钕钒酸钇激光器作为光源,利用磷酸氧钛钾晶体腔内倍频产生波长为532nm的绿光,通过轴棱锥产生了近似无衍射贝塞尔光束。推导了倍频产生的绿光的场分布,并模拟了倍频绿光经过轴棱锥产生的近似无衍射光束的轴向光强分布图和截面光强分布图。通过实验拍摄了距离轴棱锥不同位置的截面光强分布,测量了无衍射贝塞尔绿光的最大无衍射距离和中心光斑直径,实验数据与理论模拟基本吻合。实验结果说明所述方法产生的倍频无衍射绿光具有良好的光束质量,具有应用价值。     

Propagation properties of partially coherent modified Bessel–Gauss beams

Starting from the propagation law of partially coherent light, the analytical propagation equations of partially coherent modified Bessel–Gauss beams (MBGBs) through a paraxial optical ABCD system are derived and illustrated with typical application examples. Furthermore, by using the intensity moments method and integral transformation technique, the important characteristic parameters, including the beam width, far-field divergence angle, M² factor and kurtosis parameter of partially coherent MBGBs, are expressed in a closed and simple form. As a result, some basic properties of MBGBs and the dependence of the M² factor and kurtosis parameter on the spectral degree of coherence and beam order are illustrated both analytically and numerically.