Influence of Atomic Motion on a Microlaser in an Optical Standing—Wave Cavity

We study the microlaser in an optical standing-wave cavity injected with two-level atoms.The results have shown the obvious influence of atomic centre-of-mass motion on the microlaser,such as the photon distribution,the linewidth and the frequency shift.It was found that when the momentum of atoms is comparable to that of photons,the influence of atomic motion is dominated and the number of photons in the microlaser can be greatly enhanced,owing to part of the atomic kinetic energy being transferred to the resonator.This work provides a comparison of the related studies on the atomic motion under special assumptions.     

Calculation of the photoelectron spectra under a scaling transform

By solving the time-dependent Schro¨dinger equation, the dependence of photoelectron energy spectra on the binding energy of targets, wavelength and the intensity of laser pulse is exhibited and a scaling law of kinetic energy spectra of both the direct and the rescattered photoelectrons is concluded. The scaling law provides a convenient tool to determine the equivalent photoionization process of various atoms or molecules in various laser fields. The verification of the scaling law by independent methods provides incontestable support to the validity of the scaling law.     

Imprints of molecular orbitals using photoelectron angular distribution by strong laser pulses of circular polarization

We theoretically investigate the strong-field ionization of H+2 molecules in four different electronic states by calculating photoelectron angular distributions in circularly polarized fields. We find that the structure of photoelectron angular distribution depends on the molecular orbital as well as the energy of the photoelectron. The location of main lobes changes with the symmetric property of the molecular orbital. Generally, for molecules with bonding electronic states, the photoelectron's angular distribution shows a rotation of π/2 with respect to the molecular axis, while for molecules with antibonding electronic states, no rotation occurs. We use an interference scenario to interpret these phenomena. We also find that, due to the interference effect, a new pair of jets appears in the waist of the main lobes, and the main lobes or jets of the photoelectron's angular distribution are split into two parts if the photoelectron energy is sufficiently high.     

Calculation of the photoelectron spectra under the scaling transform

By solving time-dependent Schrödinger equation, the dependence of photoelectron energy spectra on the binding energy of targets, wavelength and intensity of laser pulse is exhibited and a scaling law of kinetic energy spectra of both the direct and the rescattered photoelectrons is concluded. The scaling law provides a convenient tool to determine the equivalent photoionization process of various atoms or molecules in various laser fields. The verification of the scaling law by independent methods provides an incontestable support to the validity of the scaling law.     

Entanglement dynamics of two qubits coupled by Heisenberg XY interaction under a nonuniform magnetic field in a spin bath

This paper investigates the entanglement dynamics of a Heisenberg XY model for a two-spin system in the presence of a nonuniform magnetic field.The master equations and the concurrence evolution equations for the initial α state are derived and analysed.It is shown that for the symmetric initial α state,only the nonuniform field can play a role in entanglement dynamics while the uniform field and the bath will not play such a role.For the asymmetric α state,the nonuniform field leads to the beat pattern oscillation of the concurrence evolution.The inhomogeneity of the field can enhance the entanglement by suppressing the decoherence effects of both the spin-orbit interaction and the spin bath.     

单周期激光脉冲序列作用下H原子光电离率的不对称性

采用非微扰散射理论，分别研究了线偏振的单周期激光脉冲序列以及圆偏振的单周期激光脉冲序列作用下，H原子的光电离特性。对相反方向上的光电子的不对称性进行了研究，结果表明其不对称程度与载波－包络（CE）相位、激光强度及光电子的动能有关。线偏振时，最大电离率随CE相位变化，且不对称程度随CE相位的变化呈正弦曲线特性；圆偏振时，最大电离率是常数，不随CE相位变化，但不对称程度随CE相位的变化仍呈正弦曲线特性。     

Influence of Coulomb force between two electrons on double ionization of He-like atoms

In strong-field double ionization,two electrons are ionized by intense laser field.These two electrons move in the laser field and the state is described by a Coulomb-Volkov state,where the repulsive Coulomb state describes the relative motion of the two electrons and the Volkov state describes the center-of-mass motion of the two electrons in the laser field.In the frame of scattering theory,we derive a simple analytical formula of the double ionization of He-like atoms.The effect of the Coulomb force between two electrons on the double ionization process is discussed.Numerical studies disclose that the Coulomb force enhances the ionization rate of high-energy electrons but suppresses the ionization rate of the lowest-energy electrons.     

周期量级激光脉冲作用下原子电离不对称性研究

应用不对称性参量对周期量级强激光脉冲下原子电离分布的反演不对称性进行了定量分析.采用非微扰的散射理论解析方法和三个激光模式模拟超短脉冲,研究不对称性参量随激光强度、包络位相和脉冲宽度的变化.计算表明,这种不对称性是随着波包的绝对位相以正弦形式变化而变化,其最大不对称程度依赖于脉冲强度和脉冲宽度.随着激光强度的提高,不对称性参量是先降低到最小值然后增加.对脉冲宽度相对长、有几个周期量级的高强度激光,其不对称性具有显著的特点.因此,提高脉冲强度有助于对包络绝对位相变化的观察.     

Photoelectron Angular Distributions of Positronium in Intense Laser Field

When positronium is generated in super intense laser fields irradiated by an intense laser field, it breaks up into an electron and a positron. The momentum of the electron as well as that of the positron depends on the relative direction with respect to the laser propagation. Thus, the photoelectron angular distributions show inversion asymmetry. The inversion asymmetry becomes notable for higher kinetic energy of electrons.     

INTERACTION BETWEEN A MOVING ATOM AND AN ELECTROMAGNETIC WAVE

Dynamics of a two-level atom moving in an electromagnetic field is studied. The atomic motion gives rise to a momentum-dependent detuning which holds back the atomic transition, and leads to a momentum-dependent Rabi oscillation which causes an overlapping among different Rabi oscillations. When the field is in a Fock state, the atomic population and the mean momentum of the atom exhibit damping oscillation, the damping rate is related to the momentum distribution; the collapse-revival phenomena of the atomic population and the mean momentum will occur if the atomic momentum has some special distribution. When the field is in a superposition state, the collapse-revival phenomena are modified by the atomic momentum distribution and disappear for the wider atomic momentum wavepackets. We also find that each atomic level will split into two sublevels with the same energy difference when the field is in a Fock state and the atom has a definite momentum.