共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
In this paper, we have used the finite-difference time-domain (FDTD) method to analyze the optical pulse propagation in a nonlinear, one-dimensional photonic crystal (1DPC). Hyperbolic secant pulses with various carrier wavelengths are utilized in this study. In a nonlinear regime, a 1DPC introduces a photonic band-gap whose central wavelength and width depend on the input pulse intensity. In the present work, three different cases are considered. These correspond to the carrier wavelengths of the incident pulses being out of, near to, and partially in the band-gap. For each case, the effect of nonlinearity on pulse propagation is investigated. Also, we have analyzed the two-frequency regime, in which each of the two pulses has a different carrier frequency (wavelength). This kind of study can be done directly with FDTD without any further computational burden but it is somewhat complicated using nonlinear coupled-mode equations (NLCME) and nonlinear Schrödinger equation (NLSE), which require separate treatments for each carrier wavelength. 相似文献
3.
By calculating the momenta of a coupled set of nonlinear equations of laserpulse-plasma wave interaction in the weak relativistic approximation,the conditions for fre-quency up-shift have been found.That the energy change of the pulse due to frequency shiftis compensated by the change of plasma wave energy results in photon number conservation.Some factors that affect the frequency up-shift are studied.It is also found that the laser pulsecan be compressed when it is located near the valley of plasma density perturbation and ifsome threshold value of the plasma wave field is exceeded. 相似文献
4.
Adaptive split-step Fourier method for simulating ultrashort laser pulse propagation in photonic crystal fibres 下载免费PDF全文
In this paper, the generalized nonlinear Schr\"{o}dinger equation (GNLSE) is
solved by an adaptive split-step Fourier method (ASSFM). It is found that
ASSFM must be used to solve GNLSE to ensure precision when the soliton
self-frequency shift is remarkable and the photonic crystal fibre (PCF)
parameters vary with the frequency considerably. The precision of numerical
simulation by using ASSFM is higher than that by using split-step Fourier
method in the process of laser pulse propagation in PCFs due to the fact
that the variation of fibre parameters with the peak frequency in the pulse
spectrum can be taken into account fully. 相似文献
5.
6.
We propose a three-dimensional (3D) finite-difference time-domain (FDTD) method to analyze the pulse propagation characteristics in microstructured optical fibers (MOFs). The computation domain size is greatly reduced by adopting the technique of moving problem space. The propagating pulse is virtually held in the buffer cell of the problem space as simulation continues. This method is capable to investigate the temporal evolution of the propagating pulse. Spectral information can be obtained by Fourier analysis. As an example, the influence of the kerr nonlinearity on the optical pulse propagation in a Lorentz dispersive MOF is demonstrated. The model is also used to simulate the nonlinear interactions between the pump spectral broadening and third harmonic generations in a highly nonlinear fused silica nanowire with good agreement with the generalized nonlinear envelop equation (GNEE) model. 相似文献
7.
Aleksej Mialitsin Stefan Schmult Ilia A. Solov’yov Brian Fluegel Angelo Mascarenhas 《Superlattices and Microstructures》2012
Optical pumping of a type-I/type-II coupled asymmetric quantum well pair induces a spatially separated two dimensional charge carriers plasma in the well’s wide and narrow parts. Treating the two coupled wells as a single system we find that the eigenstate probability distribution localizes exclusively either in the wide or the narrow parts of the well pair. The energy of the narrow-well localized state determines the minimal excitation energy for optically pumped charge carriers separation. In a previously used design [Guliamov et al., PRB 64 035314 (2001)] this narrow well transition energy was measured to correspond to a wavelength of 646 nm. We propose modifications to the design suggested earlier with the purpose of pushing up the energy required for the optical pumping of the two-dimensional plasma into the green and blue regions of the visible spectrum. 相似文献
8.
9.
本文提出了一种研究超短光脉冲在介质中传输特性的简单的计算机计算方法.用该方法得到了正色散光纤中的频率调制、频谱加宽和方波自成形,以及负色散光纤中的一、二、三阶孤子传输.其数值计算结果与解非线性薛定谔方程的数值结果完全一致. 相似文献
10.
Time evolution characteristic of few-cycle pulse propagating in a ladder-type atomic medium is investigated. It is shown that, time evolution of few-cycle pulse has significant difference in the both cases on- and non-resonance. In the non-resonant case, if the pulse central frequency is twice as large as medium atomic transition frequency, the pulse form (including carry-envelope phase, pulse duration, oscillation amplitude and frequency) remains unchanging or remains unchanging basically (only carry-envelope phase has some variation) in the propagation process, which means that self-induced transparency (SIT) or approximate transparency phenomenon appears. However, in the resonant case, the pulse form changes obviously in the propagation process. In addition, there is evident difference in the propagating velocity for on- and non-resonance when the pulse area is smaller. 相似文献
11.
采用时域有限差分法和傅里叶变换对电磁脉冲作用于建筑墙体后发生的反射和透射进行了比较全面的研究分析。采用周期边界实现了不同建筑墙体对电磁脉冲响应的数值计算,对计算的结果进行了讨论分析,研究结果表明:钢筋阵对低频段的屏蔽效果很好,当频率增加时,屏蔽效果变差。混凝土墙的频域波形具有明显的周期性,存在许多谐振频率,谐振时透过很大,谐振频率由墙的厚度、磁导率和介电常数决定,要提高墙的屏蔽效果必须增加墙的电导率,以达到一个比较好的屏蔽效果。钢筋混凝土墙的屏蔽效果和反射特性由钢筋和混凝土墙共同调制决定。 相似文献
12.
运用时域有限差分法计算了地面有限长电缆在高功率微波、超宽带和核电磁脉冲作用下的外导体感应电流。计算结果表明:场强相同情况下,核电磁脉冲在电缆上感应的电流最大,持续时间最长,高功率微波和超宽带在几m长和几十m长的电缆上感应的电流相差不大;入射角对电缆感应电流也有影响,电场方向与电缆平行时感应最强;地面电缆的感应电流振荡频率比自由空间中电缆的感应电流振荡频率低;随着大地电导率的增大,感应电流反射波衰减加快;电缆任一端接地后,接地端电缆感应电流都会增大。 相似文献
13.
14.
Dynamics of cooperative emissions in a cascade three-level molecular system driven by an ultrashort laser pulse 下载免费PDF全文
This paper investigates the dynamics of cooperative emissions in a cascade three-level system driven by an ultra, short laser pulse by solving numerically the full-wave Maxwell-Bloch equations. The 4, 4'-bis(dimethylamino) stilbene molecule is used as the model molecule because of its strong two-photon absorption property. The two-colour cooperative emissions are studied as functions of molecular number density and dephasing rate of the dipole coherence. The propagation effects on the evolution of the cooperative radiations are also taken into account. The cooperative radiations are enhanced for large number density of the molecule, while the fast dephasing of the dipole coherence reduces the intensity of the cooperative radiations and delays the emission times or even inhibits the formation of the emissions. The delay time of the radiation decreases with the increase of the molecular number density and the propagation distance. 相似文献
15.
16.
电离层对电磁脉冲传播的影响可以用一个频域的电流密度来描述,在时域则等效为一附加的电流密度和电导率。推导了附加电流密度和电导率在时域的表达式,它们是电离层参数和作用电场的函数,并以差分方程的形式给出。高空核爆电磁脉冲(HEMP)的计算是在时域进行的,将该电流密度和电导率计算方法应用于HEMP产生和传播的自洽计算中。作为算例,计算了100 km高空核爆电磁脉冲产生和向上传播的3种情况,并对计算结果进行了比对分析。计算结果表明:电离层时域计算方法与核爆电磁脉冲计算方法的结合是合理有效的,爆点上方考虑电离层影响的HEMP要比不考虑电离层影响的结果小得多。 相似文献
17.
A new kind of parallel finite-difference time-domain (FDTD) method is used to calculate and analyze the transmission properties of photonic crystal. The effectiveness and the accuracy of parallel FDTD method were proved by the typical two-dimensional sine wave. The result shows that parallel FDTD method, which can save time effectively in electromagnetic problems with large size and long time, performs as accurate as the series one. This method, whose results shows that the photonic band gap normalized frequency moves to the low-frequency direction with the enlargement of the section area of the square cylinder and that the band gap gets thinner, is applied to simulate and analyze the two-dimensional photonic crystal and gives calculating method and analyzing accordance to calculate and analyze large-sized photonic crystal structure. 相似文献
18.
以一维不对称π共轭分子体系(DBASVP分子)为介质,在双光子共振条件下,从双光子面积定理和严格数值求解Maxwell-Bloch方程两方面出发,分别研究超短脉冲激光在该有机分子介质中的传播过程,从而探讨双光子面积的演化规律,并分析双光子面积定理的适用性.提出了一种数值模拟分子介质光限幅特性的理论方法.分子的电子结构和电偶极矩是基于密度泛函理论利用从头计算方法得到的.研究结果表明,基于慢变幅和慢变相近似以及单模场条件下的双光子面积定理不能很好地描述超短脉冲的双光子面积在该分子介质中的演化规律.基于双光子吸收的分子光限幅特性与分子介质的厚度有关.
关键词:
双光子吸收
光限幅效应
双光子面积定理
超短脉冲激光 相似文献
19.
Dynamics control of geometric quantum discord for two coupling qubits in a squeezed vacuum reservoir
We investigate the dynamics of geometric quantum discord of coupled qubits in a squeezed vacuum reservoir. The results show that there is distinct difference between the dynamics of geometric quantum discord and that of quantum entanglement near (or away from) the decoherence free subspace. We also find that the squeezed vacuum reservoir with high squeezed amplitude is more suitable for geometric quantum discord to survive. The robustness of geometric quantum discord is stronger than that of quantum entanglement. 相似文献
20.
以具有强双光子吸收特性的4,4′-二甲氨基二苯乙烯分子体系为研究对象,通过采用时域有限差分法和预估矫正法数值求解Maxwell-Bloch方程,模拟了飞秒脉冲在该分子介质中的传播过程,研究了含时电离对双光子吸收过程和光限幅行为的影响.研究结果表明,光电离使介质与光场的非线性相互作用减弱,同时自发辐射降低, 随着入射电场的增强,光电离对主脉冲演化有明显的影响.光电离使介质的光限幅失效行为减弱.随着光电离截面增加,光限幅的动力学窗口变宽,表明了光电离有利于增强介质的光限幅效应.在不同的传播距离处,脉冲传播呈现
关键词:
含时电离
双光子吸收
光限幅效应
超短脉冲激光 相似文献