多色强激光场与分子耦合制备长寿命局域模振动

讨论用多色激光场与分子耦合来抑制局域模波包的扩散，从而将能量长时间锁定在单一化学键上以便实现选键化学的可能性．用全量子理论和半经典理论分别建立了分子振动在弱激光场和强激光场中激发和演化的模型．结果表明，多色弱场无法将布居数囚禁在局域模波包上．在强场作用下，利用强激光产生的功率加宽和波包之间的干涉，有可能将布居数囚禁在基态和局域模振动态之间 关键词：     

激光场强度对NO电子态粒子数布居影响的理论研究

用含时波包方法研究了激光场强度对NO各电子态上粒子数布居的影响.在计算中,采用了四态模型.利用分裂算符傅里叶变换方法求解Schrdinger方程,得到各个电子态的波函数,从而求得各个电子态上粒子数的布居.计算结果表明,不同强度的抽运光对各个电子态上粒子数布居会产生不同的影响.通过改变激光强度可以实现对电离产率的控制,这种思想对实现原子分子过程的激光操控具有重要意义.     

差分法求解时空分布的激光动力学模型

利用速率方程理论和差分法数值计算,建立了描述激光器内部粒子数密度和光子数密度的时间演化和空间分布的动力学模型.该方法完善了普通的激光速率方程理论,为了解激光能量的时间演化和空间分布提供了较好的理论模型. 关键词： 速率方程 差分法 动力学模型 铜激光     

基片衍射对会聚激光驻波场中原子波包几率密度演化的影响

针对激光会聚铬原子沉积实验,运用标量衍射理论,通过数值模拟研究了基片衍射对会聚激光驻波场中原子波包几率密度演化的影响。结果显示基片衍射的影响会随激光中轴线与基片沉积表面距离b0的变化而变化。相对于非衍射情况,衍射效应会提高激光驻波场中会聚平面内原子波包几率密度分布的中心值,同时减小其半峰全宽。当参量b0=－0.2w0(w0为高斯光束的束腰半径)时,原子波包几率密度的会聚平面和基片沉积表面完全重合。此处,衍射时原子波包几率密度分布的中心值为1.26,其半峰全宽为5.62 nm,两者分别为非衍射时的1.1倍和0.94倍。     

失谐对开放的四能级系统无粒子数反转激光的影响

提出开放的四能级双驱动场无反转激光系统的理论模型,由电偶极和旋转波近似得到其密度矩阵方程,讨论无反转激光产生的物理机制,利用数值计算结果分析探测场和驱动场失谐对系统无反转激光增益和粒子数差的影响.     

三能级三模量子系统中探测场的增益研究

研究了三能级原子与多模光场相互作用的量子系统，从系统的密度矩阵运动方程出发讨论了无粒子数反转探测场的增益条件，发现当驱动场拉比频率取5，探测场拉比频率取1，非相干抽运取3，驱动场失谐量取3时，系统可以在偏离共振的两端获得粒子数无反转而相应的探测场获得了增益，即实现了无粒子数反转激光，其在光通信方面具有重要的应用价值。     

飞秒激光脉宽对非绝热耦合分子波包运动的影响研究

利用含时波包法研究了强飞秒泵浦-探测激光场中激光脉宽对非绝热耦合NaI分子波包运动的影响.发现波包的振荡周期随脉宽增长而增大,而振荡幅度随脉宽增长而减小.非绝热效应引起的波包在交叉区域的分裂情况影响各态布居.脉宽增长,NaI分子的激发概率增大,而解离概率减小.研究表明调节激光场脉宽可实现对波包运动的控制从而控制态布居的选择性分布.研究结果可以为实验上实现分子的光控制以及量子调控过程提供一定的参考.     

飞秒激光脉冲作用下氢原子径向和角向波包的产生与演化

采用劈裂-伪谱方法求解激光场中的含时薛定谔方程,探讨飞秒激光脉冲中氢原子波包的演化过程.研究了氢原子激发态的径向分布,角向分布、各态布居和电子云密度随时间的变化关系.在用共振激光脉冲控制氢原子波包演化的过程中径向分布、角向分布、各态布居和电子云密度随时间发生变化,但发现径向分布和角向分布在变化的过程中始终经过一些特殊点,并从理论上分析了存在这些特殊点的原因.     

开放的非共振梯型无粒子数反转激光系统非线性增益与色散的研究

本文给出了开放的非共振ladder型三能级无粒子数反转激光系统的非线性精确解,利用数值计算结果讨论了系统各参量的变化对激光场的增益和色散的影响.作者得到以下结论:当探测激光场和驱动场都共振时,无论其他参量如何变化,色散为零.当仅有探测场失谐(驱动场失谐)时,增益和色散随探测场失谐(驱动场失谐)的变化曲线分别具有偶对称性和中心对称性,当探测场和驱动场皆失谐时,这种对称性消失;适当调节探测激光场或(和)驱动场的失谐可获得最大或较大的无粒子数反转激光增益和无吸收高色散.增益和色散(粒子数差绝对值)随原子注入速率之比的增加单调增加(单调减小),且原子退出速率越大增加(减小)得越快.在探测场和驱动场适当失谐的情况下,保持系统其他参量不变,非相干泵浦速率只有在一定范围内取值时,才能获得无粒子数反转激光增益,并存在一个增益极大值.改变探测场或驱动场Rabi频率对无粒子数反转激光增益的影响与非相干泵浦速率改变时的情况类似.     

开放四能级原子系统粒子数反转或无反转激光研究

在封闭的简单四能级原子系统模型的基础上提出了开放的四能级原子系统模型.通过在电偶极和旋转波近似下,解此系统的半经典密度矩阵运动方程得其稳态线性解析解.对该稳态解的数值模拟显示:随着驱动场的Rabi频率的连续增加系统会发生由输出的无粒子数反转激光到输出粒子数反转激光的转变;随着系统退出速率或者注入速率比的连续增大,系统会发生由输出的粒子数反转激光到输出无粒子数反转激光的转变;该系统能获得无吸收高色散;在稳态,探测激光上下能级粒子数差随探测场失谐的变化曲线呈弱矩形波.     

等离子体中调制不稳定性和波包的坍缩过程

本文给出了等离子体中由动力学理论所得到的形成强湍流的高频和低频非线性电流的表达式。根据文献[2]给出的包含有质动力、自生磁场和它们的阻尼效应的方程组,我们推广了Kono等人关于调制不稳定性的分析,得到了在各种情况下由Langmuir波或横波pump波激发的纵波和横波的增长率与参量的关系式。最后,讨论了波包的坍缩动力学问题,把非线性Schrodinger方程的坍缩讨论推广到密度和场耦合的方程组的情况。 关键词：     

Theory of a laser-plasma method for detecting terahertz radiation

A theory is developed for calculating the spectrum and the shape of a terahertz wave packet from the temporal profile of the energy of the second harmonic of the laser field generated during nonlinear interaction of laser and terahertz pulses in an optical-breakdown plasma. The spectral and temporal characteristics of the second-harmonic envelope and a terahertz pulse are shown to coincide only for short laser pulses. For long laser pulses, the second-harmonic spectral line shifts to the red and its temporal profile is determined by the time integral of the electric field of terahertz radiation.     

Resonant interaction of an electromagnetic wave with an inhomogeneous plasma slab

Resonant interaction at oblique incidence of an electromagnetic wave on an inhomogeneous plasma slab is studied. The time evolution of this interaction is solved numerically from two-fluid equations, adiabatic equation for electron pressure and from Maxwell equations. It is shown that the electromagnetic energy of an incident wave is transformed both into the heat energy and into the energy of plasma oscillations in the direction of density gradient. The distribution of the transformed energy between the heat energy and the energy of plasma oscillations is strongly dependent on the plasma temperature. The ratio of heat energy to the energy of plasma oscillations is growing with growing temperature. The plasma oscillations are generated by magnetic induction of the penetrating wave. In a cold plasma they are generated especially in the overdense region and their frequency is equal to local plasma frequency. The electric field in the direction of plasma gradient has a form of a wave packet whose envelope reaches a maximum at resonance. The characteristic wavelength in the wave packet decreases and the amplitude of the packet increases with the time.     

Dynamics of electron in a surface quantum well

This paper studies the quantum dynamics of electrons in a surface quantum well in the time domain with autocorrelation of wave packet. The evolution of the wave packet for different manifold eigenstates with finite and infinite lifetimes is investigated analytically. It is found that the quantum coherence and evolution of the surface electronic wave packet can be controlled by the laser central energy and electric field. The results show that the finite lifetime of excited states expedites the dephasing of the coherent electronic wave packet significantly. The correspondence between classical and quantum mechanics is shown explicitly in the system.     

Wave Packets in a Magnetic Field

A Gaussian wave packet confined to move on a plane perpendicular to a magnetic field remains a Gaussian wave packet in its time evolution. The average position and momentum follow the Ehrenfest equations which are identical to the classical Hamilton equations. A set of nonlinear equations decoupled from the Ehrenfest equation is derived for the parameters describing the time evolution of the density distribution and phases of a wave packet. Explicit solutions are then obtained when the "internal" angular momentum of the wave packet vanishes. In this case it is shown that the motion of the wave packet is a superposition of a translational motion, a rotation and a vibration.     

The structural features of wave collapse in medium with normal group velocity dispersion

The dynamic characteristics of self-action in three-dimensional wave packets described by the nonlinear Schrödinger equation with a hyperbolic space operator were studied analytically and numerically. The class of the initial wave field distributions for which self-focusing effects predominated over dispersion spreading and caused the arising of wave collapses was considered. The collapse of tubular wave packets was shown to be accompanied by packet shape changes during its contraction to the axis of the system. The nonlinear stabilization of collapses resulted in wave field fragmentation in the longitudinal direction followed by the expansion of the bunches thus formed along the axis. The dynamics of collapses was numerically studied taking into account medium nonlinearity saturation and nonlinear dissipation.     

Two kinds of upper hybrid soliton bistability

The basic model employed to describe nonlinear upper hybrid wave structures is the generalized nonlinear Schrödinger equation including second and fourth order dispersive effects as well as local and nonlocal nonlinearity. For two kinds of such an equation the existence of two stable solitons with the same plasmon number but with different spatial scales and amplitudes is shown as two qualitatively different kinds of upper hybrid soliton bistability. An integral relation for an arbitrary nonlinear upper hybrid wave packet evolution is derived taking into account higher order dispersive effects. Necessary conditions for soliton formation from arbitrary wave packets and the impossibility of wave packet collapse are demonstrated taking into account higher order dispersive effects.     

Electric field controlled, pulsed autoionization in two electron wave packets

In this paper, control of the evolution of a two electron wave packet through the application of a static electric field is demonstrated. Specifically, application of a small electric field is used to produce pulsed autoionization events, the timing of which can be controlled on a picosecond time scale. The technique is demonstrated by exciting calcium atoms using a short-pulsed laser to the 4p(3/2)19d doubly excited state, which is energy degenerate with the 4p(1/2)nk stark states. Evolution of the resultant wave packet is monitored through the application of a second short laser pulse, which stimulates the atoms to emit a photon producing singly excited Rydberg states which are detected using field ionization.     

On the radiation pressure of electromagnetic wave packets in nondispersive fluid dielectrics

Using the classical dipole representation for the gas molecules, an approximate kinetic equation is derived including radiation pressure forces. The energy-momentum tensor for a quasimonochromatic electromagnetic wave packet is constructed. Electrostrictive forces and nonlinear perturbations of the gas rest energy density are taken into account. Certain particle-like properties of the wave packet are demonstrated. Radiation pressure forces are given for some simple models of fluid inhomogeneities.     

Effects of relativistic and ponderomotive nonlinearities on the interaction of high-power laser beam with an inhomogeneous warm plasma

The influence of relativistic-ponderomotive nonlinearities and the plasma inhomogeneity on the nonlinear interaction between a high-power laser beam and a warm underdense plasma are studied. It is clear that the relativistic ponderomotive force and the electron temperature modify the electron density distribution and consequently change the dielectric permittivity of the plasma. Therefore, by presenting the modified electron density and the nonlinear dielectric permittivity of the warm plasma, the electromagnetic wave equation for the propagation of intense laser beam through the plasma is derived. This nonlinear equation is numerically solved and the distributions of electromagnetic fields in the plasma, the variations of electron density, and plasma refractive index are investigated for two different background electron density profiles. The results show that the amplitude of the electric field and electron density oscillations gradually increase and decrease, during propagation in the inhomogeneous warm plasma with linear and exponential density profiles, respectively, and the distribution of electron density becomes extremely sharp in the presence of intense laser beam. It is also indicated that the electron temperature and initial electron density have an impact on the propagation of the laser beam in the plasma and change the plasma refractive index and the oscillations' amplitude and frequency. The obtained results indicate the importance of a proper choice of laser and plasma parameters on the electromagnetic field distributions, density steepening, and plasma refractive index variations in the interaction of an intense laser beam with an inhomogeneous warm plasma.