聚焦部分相干涡旋光束作用于不同折射率瑞利粒子上的辐射力

 使用聚焦部分相干高斯谢尔涡旋光束,对不同折射率的瑞利粒子的辐射力做了分析,着重研究了相关长度和束腰宽度对辐射力和俘获稳定性的影响。结果表明：相关长度和束腰宽度分别存在临界值,相干长度小于等于其临界值或束腰宽度大于等于其临界值时,可利用其俘获相对折射率大于1的微粒;而在相关长度大于其临界值或束腰宽度小于其临界值时,可利用其俘获相对折射率小于1的微粒。对俘获稳定性的分析表明,需选择适当的相关长度和束腰宽度才能稳定俘获瑞利粒子。     

Modulation instability in metamaterials with fourth-order linear dispersion,second-order nonlinear dispersion,and three kinds of saturable nonlinearites

The linearized nonlinear propagation equation and its coefficients, gain spectrum of modulation instability (MI) in metamaterials (MMs) with fourth-order linear dispersion, second-order nonlinear dispersion, and three kinds of saturable nonlinearites, are analytically deduced by utilizing the linear stability analysis and Drude electromagnetic model. Then variations of gain spectra of MI with the normalized angular frequencies and the optical power densities are calculated in real units. In the negative refractive region, two kinds of gain spectra are discovered. The first (second) one is close to (far from) the zero perturbation frequencies and it corresponds to the lower (higher) normalized angular frequencies. Moreover, the second one has higher cutoff frequency, which is obviously beneficial to generation of high-repetition-rate pulse trains. While in the positive refractive region, only the first kind of gain spectra is found. With increase of the optical power densities, the peak gains and the spectral widths of MI increase before decrease, but they vary the most rapidly (slowly) for the exponential (conventional) saturable nonlinearities. The MI characteristics and their corresponding applications can be adjusted by several methods.     

Modulation instability in negative refractive metamaterials with exponential saturable nonlinearity and self-steepening effects

Modulation instability (MI) in negative refractive metamaterials with exponential saturable nonlinearity and the self-steeping effect is investigated by using the standard linear stability analysis and the Drude electromagnetic model. The dispersion relation, instability condition, cut-off frequency, gain spectrum, and their corresponding dimensionless expressions are analytically deduced and then calculated. The results show that, the self-steepening effect will suppress MI by decreasing the cut-off frequency and the maximum gain. And the larger the power density ratio is, more slowly the cut-off frequency and the maximum gain decrease with increase of the self-steepening parameter. Although the sign of the self-steepening parameter does not influence MI but its absolute value must be smaller than a certain value. Depending on different self-steepening parameters, the cut-off frequency and maximum gain may decrease or increase before decrease with increase of the power density ratio. In particular, for large self-steepening parameters, the power density ratio may have a threshold value. When the power density ratio is under this threshold, MI will disappear.     

饱和非线性正折射异向介质中的调制不稳定性

直接从异向介质中包含饱和非线性、自陡峭和二阶非线性色散效应的非线性扩展传输方程出发,采用线性稳定性分析法,导出了调制不稳定性的色散关系、不稳定条件、无量纲的临界扰动频率和增益谱。计算和讨论了异向介质正折射区无量纲的增益谱随归一化角频率和入射功率密度的变化关系。结果表明,在异向介质正折射区,随归一化角频率和入射功率密度的不同,增益谱将会出现扰动频率大于零、扰动频率大于某个非零临界值、扰动频率大于零而小于某个非零临界值3种形式。在归一化角频率较小时,调制不稳定性可能出现阈值入射功率密度;且在较小的入射功率密度时,调制不稳定性只能出现在大于某个临界频率时。     

Effects of group-velocity mismatch and cubicquintic nonlinearity on cross-phase modulation instability in optical fibers

The synthetic effects of group-velocity mismatch and cubic-quintic nonlinearity on cross-phase modulation induced modulation instability in loss single-mode optical fibers have been numerically investigated. The results show that the quintic nonlinearity plays a role similar to the case of neglecting the group-velocity mismatch in modifying the modulation instability, namely, the positive and negative quintic nonlinearities can still enhance and weaken the modulation instability, respectively. The group-velocity mismatch can considerably change the gain spectrum of modulation instability in terms of its shape, peak value, and position. In the normal dispersion regime, with the increase of the group-velocity mismatch parameter,the gain spectrum widens and then narrows, shifts to higher frequencies, and the peak value gets higher before approaching a saturable value. In the abnormal dispersion regime, two separated spectra may occur when the group-velocity mismatch is taken into account. With the increase of the group-velocity mismatch parameter, the peak value of the gain spectrum gets higher and shorter before tending to a saturable value for the first and second spectral regimes, respectively.     

Propagation dynamics and optical trapping of a radial Airy array beam

Analytical propagation expression of a radial Airy array beam in coherent and incoherent combination passing through paraxial ABCD system is derived, and used to investigate the effect of combination scheme, array orientation and initial phase of Airy beamlet on propagation dynamics of the resulting beam in free space, where optical spot array and vortex array with different shapes are also found, respectively. And then taking four-beamlet Airy array beam in same array orientation as an example, square optical spot array obtained in focal field can be used for simultaneous trapping multiple Rayleigh particles with relative refractive index larger than 1. The transverse gradient forces serving as restore forces tend to push particles at different initial positions to their individual optical spot center. The analysis of trapping stability indicates that larger input peak intensity of Airy beamlet and smaller particle size are benefit to trapping particle owing to many deeper potential wells. Vortex array produced by coherent combined Airy array beam in this paper is expected to be useful for simultaneous trapping microparticles with relative refractive index smaller than 1.     

Two-photon and Three-photon Fluorescence of Triton X-100 in the Ultraviolet Region

Journal of Fluorescence - We report, to our best knowledge, the first observation of two-photon and three-photon fluorescence of Triton X-100 (TX-100) in water and cyclohexane. The observed...     

过渡金属铬调控光催化环化反应研究进展

如何运用更加经济、环境友好的方式制备具有生物/药理活性的化合物是有机合成、生物医药领域的重要问题。近年来发展的过渡金属催化光氧化还原反应为解决上述问题提供了契机。其中,相对于传统的钌/铱络合物催化剂,新型第一周期过渡金属铬催化剂在该领域的开发及应用备受关注。烯/炔的[2+N]环化反应是过渡金属光敏试剂催化的一个经典反应类型,通常表现出高化学、区域及立体选择性,而且产物是很多药物分子的基本结构单元,本文围绕铬调控光催化[2+N]环化反应以及机理研究进行综述,并对其中有待进一步研究的方向进行展望,希望为铬调控光催化环化反应的深入理解以及新型光氧化还原催化剂在该类反应中的发展提供启发。     

Evolution of hyperbolic-secant optical pulses towards wave breaking in quintic nonlinear fibers

Evolutions of the frequency chirps, shapes, and spectra of initial hyperbolic-secant pulses towards wave breaking are numerically investigated in the normal dispersion regimes of optical fibers with quintic nonlinearity and the developing chirps and the characteristic distances of wave breaking are analytically processed approximately. The results show that quite different mathematical expressions from those of initial Gaussian pulses are obtained. Moreover, the wave breaking here will be more intense for more oscillation peaks will appear in the pulse wings and the breaking process will last longer distance before rectangle-shaped pulses form at last. However, the quintic nonlinearity plays a similar role to the case of initial Gaussian pulses in developing chirps and bringing forward or retarding the wave breaking. The wave breaking distance will also decrease with increase of the quintic nonlinearity and the soliton order.