强激光场中模型氢原子和真实氢原子产生高次谐波的比较

通过数值求解原子在强激光场中的含时薛定谔方程,研究了有库仑奇点和无库仑奇点的一维模型氢原子和三维真实氢原子产生高次谐波的特性.结果表明,有库仑奇点和无库仑奇点的一维模型氢原子和三维真实氢原子产生高次谐波的截止位置相同,但是高次谐波强度变化特征明显不同,进一步的研究表明,无库仑奇点的模型氢原子产生的高次谐波谱相对变化趋势与三维真实氢原子的高次谐波谱变化趋势是完全一致的.     

强激光场中模型氢原子和真实氢原子产生高次谐波的比较

通过数值求解原子在强激光场中的含时薛定谔方程,研究了有库仑奇点和无库仑奇点的一维模型氢原子和三维真实氢原子产生高次谐波的特性。结果表明,有库仑奇点和无库仑奇点的一维模型氢原子和三维真实氢原子产生高次谐波的截止位置相同,但是高次谐波强度变化特征明显不同,进一步的研究表明,无库仑奇点的模型氢原子产生的高次谐波谱相对变化趋势与三维真实氢原子的高次谐波谱变化趋势是完全一致的。     

强激光场中模型氢原子的势函数对产生高次谐波强度的影响

在保证一维模型氢原子基态能量不变的前提下,通过构造一个可调参数的势函数,研究了在单个周期和多个周期激光作用下,取不同参数势函数一维模型氢原子产生的高次谐波谱规律.结果表明,在过垒电离区域,一维模型氢原子的高次谐波强度与势函数势阱的深度有关,与势函数是否存在库仑奇点没有直接关系. 关键词： 强激光场 一维模型氢原子 势函数 高次谐波     

强激光场中长程势与短程势原子产生高次谐波与电离特性研究

用数值方法求解含时薛定谔方程，研究了具有长程势和短程势的一维原子在强激光场中的高次谐波和电离特性. 在强激光场中，长程势和短程势原子产生的高次谐波具有相似的特性，对应的平台和截止位置相同，但是短程势原子没有低阶的高次谐波，而长程势和短程势原子在激光场中的电离概率明显不同. 研究结果表明，原子的激发态结构对低阶的高次谐波和原子的电离概率有重要影响. 关键词： 强激光场 高次谐波 电离概率     

超强激光场中氢原子辐射高次谐波蒙特卡罗模拟

运用蒙特卡罗方法，模拟和计算出在超强激光场中，氢原子在相对论领域的电离几率和辐射出的高次谐波，并且讨论了氢原子的电离几率和辐射出的高次谐波与激光场的电场和磁场的关系。     

双色激光场对氢原子高次谐波的影响

为了深入研究高次谐波产生的多光子过程,使用劈裂算符结合拟谱的方法对氢原子在双色强激光场中的高次谐波辐射作了数值模拟计算,结果显示,当附加一适当双色激光场时,高次谐波谱的平台区大幅提高和展宽.根据计算结果提出的混合跃迁道理论,成功解释了高次谐波谱所呈现的细节特征.     

脉冲形状对氢原子高次谐波的影响

在含时密度泛函理论框架下,采用经典和量子相结合的模型,模拟了氢原子在超强飞秒激光脉冲作用下的高次谐波产生现象,并研究了激光脉冲形状对氢原子高次谐波的影响.结果表明,氢原子的高次谐波谱具有典型的原子谐波谱的特征;具有“下降－平台－截止”的结构和偶次谐波被禁闭仅出现奇次谐波的选择性特征;不同的脉冲形状会导致高次谐波的截止频率和谱线强度的变化.     

非对称波形激光驱动的氢原子高次谐波频移及控制

提出了一种利用非对称波形激光脉冲与原子相互作用在隧穿区发射高次谐波谱的大频移方案.通过数值求解偶极近似下的三维含时薛定谔方程,研究了该激光驱动氢原子发射的高次谐波特性.结果表明,利用上升沿与下降沿不同的非对称激光驱动氢原子所发射的高次谐波在截止位置附近发生了大的频率红移和蓝移,通过改变激光脉冲的上升沿或下降沿,能调控谐波的频移量.产生频移的原因是激光脉冲上升沿或下降沿对谐波贡献的不同所致,当下降沿发射谐波的贡献大于上升沿的贡献时,谐波发生红移,反之则发生蓝移.通过改变激光脉冲波形,在隧穿电离区能够调控截止位置附近原子发射的高次谐波频率,对于给定的某一阶谐波,调控的范围可从奇次阶到邻近偶次阶之间的任意频率处.     

双色激光场中高次谐波转化效率的提高

采用渐近边界条件和辛算法数值求解双色激光场与模型P?schl-Teller势相互作用的含时Schr?dinger方程，计算了电离概率、平均位移、高次谐波以及跃迁概率；数值结果显示添加6倍频光的双色激光场能使高次谐波转化效率明显提高.分析了双色激光场极大地提高高次谐波转化效率的机理，并且通过对产生特定级次谐波的跃迁概率的计算，给出高次谐波转化效率提高的具体数值. 关键词： 渐近边界条件 辛算法 双色激光场 高次谐波     

电四极矩对高次谐波产生的贡献

通过数值求解强场近似下单电子原子的含时薛定谔方程,研究了在强线偏振激光场下,氢原子电四极矩对高次谐波产生的贡献.研究结果表明,在强激光场的作用下,在偶极矩的影响下氢原子能够产生奇次谐波,当激光场强度增加到一定值时,氢原子在电四极矩的作用下产生了偶次谐波.根据谐波功率谱和时频分析图并结合半经典"三步模型"分析了偶次高次谐波产生机制,并对产生的物理现象做出了合理的解释.     

Floquet study of ionization and high-order harmonic generation for a hydrogen atom in high-frequency laser fields

In this paper, we investigate the dynamics of a hydrogen atom in high-frequency (several atomic units) super strong (up to several tens of atomic units) laser fields within the high frequency Floquet theory framework. The ionization rate, ionization spectrum, angular distribution and high-order harmonic generation are all investigated. Our studies reveal the universal behavior of the total ionization rate, excess-photon ionization spectrum and angular distribution of the ionization rate in the stabilization regime, and achieve a deep insight into the dynamics of high-order harmonic generation in the stabilization regime. Received 6 June 2001 and Received in final form 31 August 2001     

势函数对强激光辐照下原子高次谐波辐射的影响

理论上研究了中红外强激光分别与长程库仑原子和短程势模型原子相互作用产生的高次谐波辐射.发现在相同激光参数条件下,与长程库仑原子的谐波辐射相比,短程原子具有更低的辐射效率,但在高频区域(接近cutoff位置),二者效率相似.通过对谐波辐射的时间频率分析发现,在短程模型原子谐波辐射中,长轨道发挥更重要的作用.利用其产生的高次谐波辐射,可以产生孤立阿秒脉冲.     

激光强度依赖的阈下谐波产生机制

利用广义伪谱方法精确数值求解了氢原子在强激光场中的三维含时薛定谔方程,获得了强激光中氢原子的含时波函数,利用时间依赖的偶极矩的傅里叶变换得到了高次谐波谱,研究了氢原子在强激光场中发射低于电离阈值的谐波谱对激光强度的依赖性.研究发现,激光强度在低于电离阈值的谐波产生的通道选择的过程中扮演着重要角色,主要有两种量子通道对阈下谐波的产生有贡献,即广义的短轨道和长轨道,其中长轨道对激光场强度比较敏感.结合小波时频变换、经典轨道分析、以及强度依赖的量子通道选择分析,本文阐明了其背后的物理机制.     

Single Ultrashort Attosecond Pulse Generation via Combination of Chirped Fundamental Laser and an Ultraviolet Controlling Pulse

We theoretically study the high-order harmonic generation (HHG) from a hydrogen atom in an intense few-cycle chirped fundamental laser in combination with an ultraviolet (uv) controlling pulse.The high-order harmonic spectrum is calculated by solving the time-dependent Schr¨odinger equation using the split-operator method.In our calculation,we present the difference of the high-order harmonic spectrum from one-dimensional (1D) model hydrogen atom and three-dimensional (3D) real hydrogen atom.We found that the plateau of the high-order harmonic generation from the 1D case and 3D case are all extended effectively to I p + 35U p due to the presence of the chirped laser pulse and the HHG supercontinuum spectrum is generated by adding an ultraviolet controlling pulse at a proper time,but the efficiency of the HHG for 3D case is more higher at the near cut-off region than the 1D case.Therefore,the generation of the attosecond pulse by synthesizing the harmonics near cut-off region have some slight differences between 1D and 3D simulations.As a real 3D case study,we show that an isolated 18 as pulse with a bandwidth of 232.5 eV is generated directly by optmizing the combination laser fields.     

Ionization of a molecular hydrogen ion by a strong low-frequency electromagnetic field of laser radiation

Simple analytical expressions are obtained for the energy and angular distributions of outgoing electrons in ionization of a molecular hydrogen ion by a strong low-frequency electromagnetic field as well as for the ionization probabilities per unit time. The cases of linear and circular polarization of the laser radiation are studied. It is shown that in contrast to the case of the ionization of atoms oscillations appear in the energy spectra of the photoelectrons as a function of their kinetic energy. The well-known limits for the tunneling ionization probabilities for the hydrogen atom by a strong low-frequency alternating field are obtained in the case of large internuclear separations. Zh. é ksp. Teor. Fiz. 113, 583–592 (February 1998)     

Molecular imaging using high-order harmonic generation and above-threshold ionization

Accurate molecular imaging via high-order harmonic generation relies on comparing harmonic emission from a laser-irradiated molecule and an adequate reference system. However, an ideal reference atom with the same ionization properties as the molecule is not always available. We show that for suitably designed, very short laser pulses, a one-to-one mapping from high-order harmonic frequencies to electron momenta in above-threshold ionization exists. Comparing molecular and atomic momentum distributions then provides the electron recollision amplitude in the molecule for enhanced molecular imaging. The method retrieves the molecular recombination transition moments highly accurately, even with suboptimal reference atoms.