Compton散射对等离子体零色散附近调制不稳定性的影响

应用Compton散射模型和非线性Schrdinger方程,研究了Compton散射对等离子体零色散附近调制不稳定性的影响,提出了将Compton散射作为形成调制不稳定性的新机制,给出了等离子体修正色散方程,并进行了数值计算.结果表明:二阶色散较大时,远离零色散附近调制不稳定性增益谱由入射和散射光产生的二阶色散决定,随二阶色散增大,四阶色散作用迅速减小,这是因散射效应有效削弱了四阶效应的缘故.零色散附近调制不稳定性增益谱由入射和散射光产生的四阶色散决定,二阶色散被湮灭,微扰频率最大值向临界微扰频率较快靠近,这是因散射效应有效增强了四阶效应的缘故.增益谱宽随等离子体损耗增大而迅速增大,这是因功率增大使散射效应增强,导致带电粒子辐射阻尼增强的缘故.     

饱和非线性下零色散附近的交叉相位调制非稳

从光纤中扩展的耦合非线性薛定谔方程组出发,在饱和非线性光纤零色散附近,研究了不同二、四阶色散参量下交叉相位调制不稳定性增益谱及其临界扰动频率、谱宽和谱峰随两光波入射功率的演化特点.研究表明,随色散参量不同,增益谱随两光波入射功率的增大可能出现三种演化形式：一是始终是两个分离的谱区;二是由开始时的两个合成一个,最后再分离成两个;三是始终是一个谱区.饱和非线性的存在则使每个谱区的谱宽、谱峰及远离零点的临界扰动频率,随两光波入射功率的增大可能呈现出先增大后减小的特点,使第二谱区靠近零点的临界扰动频率呈现先减小后增大的特点,从而可能出现两个不同的输入功率对应同一个增益峰值和谱宽的情形.色散参量对增益谱的谱峰影响小,对谱宽影响大.越靠近零色散区,每个谱区谱宽越大,越易连成一个谱区.     

色散磁导率对异向介质中的调制不稳定性的影响

基于Drude模型研究了异向介质的色散磁导率对调制不稳定性的影响. 结果表明,在反常色散情形,赝五阶非线性在异向介质的负折射区中增大了调制频谱的范围及增益值,这与常规正折射介质中出现的现象正好相反;自陡峭效应在异向介质中有可能为负值,但无论正负,也无论在正折射区还是负折射区,它都抑制调制不稳定性的产生;二阶非线性色散效应在正、负折射区中分别促进和抑制调制不稳定性的产生. 在正常色散情形,由于二阶非线性色散效应的作用,使本来在常规正折射介质中不可能出现的调制不稳定性现象也能出现,这一特性为在正常色散区形成孤 关键词： 异向介质 调制不稳定性 色散磁导率 二阶非线性色散     

色散磁导率对异向介质中的调制不稳定性的影响

基于Drude模型研究了异向介质的色散磁导率对调制不稳定性的影响. 结果表明，在反常色散情形，赝五阶非线性在异向介质的负折射区中增大了调制频谱的范围及增益值，这与常规正折射介质中出现的现象正好相反；自陡峭效应在异向介质中有可能为负值，但无论正负，也无论在正折射区还是负折射区，它都抑制调制不稳定性的产生；二阶非线性色散效应在正、负折射区中分别促进和抑制调制不稳定性的产生. 在正常色散情形，由于二阶非线性色散效应的作用，使本来在常规正折射介质中不可能出现的调制不稳定性现象也能出现，这一特性为在正常色散区形成孤     

非线性管理光纤光栅中的调制不稳定性研究

基于非线性耦合模方程,研究了非线性管理光纤光栅中的调制不稳定性,得到了调制不稳定性的色散关系。与常规的非线性光纤光栅相比,在非线性管理光纤光栅中,克尔非线性的变化改变了调制不稳定性增益谱的谱宽和幅度,并导致新的不稳定性区域的出现:在反常色散区,原来关于零波数对称的两个旁瓣随着克尔非线性变化的增加其增益幅度递减至零,在经历了一段无增益区域之后,又逐渐形成了在零波数附近区域的一个新的单峰;而在正常色散区,除了原来的两个增益区域之外,零波数附近出现了新的增益区,增益的幅度随克尔非线性变化的增加而递增。可见,非线性管理光纤光栅给调制不稳定性的产生提供了更多的空间。     

受激拉曼散射对非线性介质波导的时空不稳定性影响

基于非线性包络方程我们研究了平面非线性介质波导中的时空不稳定性,得到了有拉曼散射效应情形下不稳定性调制的增益谱的表达式.结果表明在正常和反常两种群速度色散情形下,拉曼散射效应都会导致出现新的不稳定性区域,并且使原有的每一个谱分量的增益上升从而使谱的范围扩大.并通过分析反常色散情况下四种不同函数分布的非线性色散介质系数对不稳定性增益谱的影响,得到呈双曲函数分布的非线性色散介质最为理想.     

具有饱和非线性的非克尔光纤的调制不稳定性

理论上分析了当存在高阶色散时具有饱和非线性的非克尔光纤的调制不稳定性.三阶色散对调制不稳定性没有影响,四阶色散效应导致在正常和反常色散区出现了新的调制不稳定区.并且对比了不同他和参数的增益谱,在新的调制不稳定区,发现同样有一个临界调制频率对应两个入射功率的现象.     

四阶色散和五阶非线性对零色散附近交叉相位调制不稳定性的综合影响

从包含高阶色散和高阶非线性的广义非线性薛定谔方程出发,研究了零色散附近交叉相位调制不稳定性增益谱,分析了四阶色散和五阶非线性系数对增益谱的影响.结果表明：当光脉冲工作在零色散附近时,四阶色散对交叉相位调制不稳定性起决定作用,它使增益谱变宽.正（负）五阶非线性使增益谱的谱宽和峰值增大（减小）.随着二阶色散的增加,四阶色散对增益谱的影响越来越小.     

五阶非线性下零色散附近的调制不稳定性

在同时考虑光纤损耗、高阶色散以及高阶非线性情况下,从广义非线性薛定谔方程出发,研究了零色散附近的调制不稳定性,分析了四阶色散和五阶非线性对增益谱的影响.结果表明：当光脉冲工作在零色散附近时,四阶色散对调制不稳定性起决定作用,它使反常色散区的增益谱变宽.在光纤正常色散区,正（负）五阶非线性使增益谱的谱宽和峰值增大（减小）;但在反常色散区,五阶非线性仅改变增益谱的峰值,几乎不影响谱宽.     

Compton散射对五阶非线性下零色散附近调制不稳定性的影响

应用多光子非线性Compton散射模型和非线性薛定谔方程,研究了Compton散射对五阶非线性零色散附近调制不稳定性的影响.将入射光和Compton散射光作为产生调制不稳定性的机制,分析了光纤损耗、四阶色散和五阶非线性对增益谱的影响.结果表明:散射下的正或负五阶非线性分别使零色散附近的增益谱宽和峰值比散射前增大得更大或...     

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.     

Retrieval of high-order susceptibilities of nonlinear metamaterials

Active metamaterials embedded with nonlinear elements are able to exhibit strong nonlinearity in microwave regime.However, existing S-parameter based parameter retrieval approaches developed for linear metamaterials do not apply in nonlinear cases. In this paper, a retrieval algorithm of high-order susceptibilities for nonlinear metamaterials is derived.Experimental demonstration shows that, by measuring the power level of each harmonic while sweeping the incident power,high-order susceptibilities of a thin-layer nonlinear metamaterial can be effectively retrieved. The proposed approach can be widely used in the research of active metamaterials.     

Impacts of higher-order dispersions and saturable nonlinearities on modulation instability in negative-refractive metamaterials

On the basis of the standard linear stability analysis and Drude electromagnetic model,the impacts of higher-order dispersions and three kinds of typical saturable nonlinearities on modulation instability(MI) have been analyzed and calculated for negative-refractive metamaterials(MMs).Our results show that the MI gain spectra consist of only one spectral region instead of one or two regions in ordinary materials,which may be close to or far from the zero point.Particularly,the spectrum far from the zero point has a high cut-off frequency but a narrow spectral width,which is obviously beneficial to the generation of high-repetition-rate pulse trains.Moreover,MI characteristics here will vary with the normalized angular frequency which can be modified by adjusting the structures of negative-refractive MMs,signifying the controllability of bistable solitons and MI based applications.The effects of saturable nonlinearities are similar to those in ordinary materials.     

包含高阶色散的色散缓变光纤中交叉相位调制不稳定性分析

从包含高阶色散的广义非线性薛定谔方程出发,得到了色散缓变光纤中交叉相位调制不稳定增益谱,研究了增益谱随入射功率及光纤纵向色散参量的变化关系.结果表明：由于四阶色散的影响,在色散缓变光纤的正、反常色散区,交叉相位调制不稳定均发生在两个频谱区.反常色散区两频谱区宽度均比正常色散区宽,且反常色散区第二频谱区更靠近零点,说明色散缓变光纤中交叉相位调制不稳定更容易发生在反常色散区.增益谱宽都随两入射光波功率比值的增加而增大.色散缓变光纤中交叉相位调制不稳定增益谱宽比常规光纤的宽,且随着光纤纵向色散参量μ的增大色散缓变光纤中交叉相位调制不稳定越来越明显.     

具有电与磁非线性效应超常介质中光束的聚焦特性

基于Drude模型,采用解析法与数值模拟法研究了具有电与磁非线性效应超常介质中光束的聚焦特性。结果表明超常材料中光束聚焦现象不但可以发生在自聚焦非线性介质中(正折射区)而且可以发生在自散焦非线性介质中(负折射区),且光束中心频率离介质的等离子频率越近,其聚焦效应越明显。特别是当电与磁非线性极化率为异号时,超常介质的非线性符号可以通过调控电与磁等离子频率的相对大小控制,这为主动操控光束的传输提供一种新的自由度。     

Experimental demonstration of near-infrared negative-index metamaterials

Metal-based negative refractive-index materials have been extensively studied in the microwave region. However, negative-index metamaterials have not been realized at near-IR or visible frequencies due to difficulties of fabrication and to the generally poor optical properties of metals at these wavelengths. In this Letter, we report the first fabrication and experimental verification of a transversely structured metal-dielectric-metal multilayer exhibiting a negative refractive index around 2 microm. Both the amplitude and the phase of the transmission and reflection were measured experimentally, and are in good agreement with a rigorous coupled wave analysis.     

Reflection of a focused light beam in a medium with Kerr nonlinearity. I. Estimates in the paraxial-beam approximation

The reflection intensity in a nonlinear dielectric layer is calculated in the approximation of paraxial incident and reflected light beams. It is shown that reflection is mainly determined by discontinuities of the refractive-index on the boundaries. Unlike reflection by a linear dielectric layer, reflection by a nonlinear layer occurs with a three-time decrease in the effective reflection area and the corresponding broadening of the angular spectrum. The intensity of the reflected wave is comparable to that of an incident wave with nearly critical beam power.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 7, pp. 867–875, July, 1996.This work was supported by the International Science Foundation and the Russian Federation Government (projects MR1000 and MR1300).     

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.     

Correlated ejection of electron-hole drops from a continuously generated electron-hole liquid in Ge

The photocurrent power spectra were measured in a Ge photodiode as a function of the incident optical intensity at 1.8 K and 4.3 K. The observed spectra showed a peak at low frequencies superimposed on a continuum which has a cut-off at high frequency. The interpretation of the results implies that the electron-hole drops coming from a same region of the photoexcited liquid are ejected periodically.     

高功率垂直外腔面发射半导体激光器增益设计及制备

垂直外腔面发射半导体激光器(vertical external cavity surface emitting laser, VECSEL)兼具高功率与良好的光束质量,是半导体激光器领域的持续研究热点之一.本文开展了光抽运VECSEL最核心的多量子阱增益区设计,对量子阱增益光谱及其峰值增益与载流子浓度及温度等关系进行系统的理论优化,并对5种不同势垒构型的量子阱增益特性进行对比,证实采用双侧GaAsP应变补偿的发光区具有更理想的增益特性.对MOCVD生长的VECSEL进行器件制备,实现了VECSEL在抽运功率为35 W时输出功率达到9.82 W,并且功率曲线仍然没有饱和;通过变化外腔镜的反射率, VECSEL的激光波长随抽运功率的漂移系数由0.216 nm/W降低至0.16 nm/W,证实外腔镜反射率会影响VECSEL增益芯片内部热效应,从而影响VECSEL激光输出功率.所制备VECSEL在两正交方向上的发散角分别为9.2°和9.0°,激光光斑呈现良好的圆形对称性.