Dynamics of electronic and nuclear motion in a molecular hydrogen ion in a strong laser field

The dynamics of the electron and ion subsystems of a molecular hydrogen ion in the field of femtosecond titanium-sapphire laser radiation is investigated by using numerical simulation. The dependence of the probability of ionization and excitation of various electron states of H ₂ ⁺ on the radiation intensity and on the orientation of the molecule axis relative to the direction of polarization of the electric field of the wave is investigated. It is shown that the population of all electronic states of the molecule (except the ground state and the first excited state) is negligibly low in a wide range of radiation intensity. In such a situation, if the probability of system ionization is also low, the dynamics of vibration-rotation motion of nuclei in the molecule can be considered in the approximation of two potential surfaces (energy levels). The possibility of the effective orientation of the molecular axis along the direction of the electric field of the wave in the absence of dissociation of the system is considered.     

Multiphoton ionization of molecular hydrogen by single-cycle pulses

Multiphoton ionization, first observed by N.B. Delone in 1965, has been a subject of intense studies ever since. In this paper we consider multiphoton ionization of molecules in the limit of subopticalcycle pulse duration. Moreover, we study the regime where the molecules are first prepared in a coherent vibrational superposition state, and then are subjected to sub-cycle laser pulses synchronized with respect to the phase of the coherent molecular motion. The present approach is based on the Keldysh formalism, which assumes that the final free electron’s state is much more sensitive to the pulse than the bound initial wavefunction [1]. We find that the ionization rate depends not only on the sub-cycle shape of the laser pulses, but also on the time delay between the arrival of pulses and molecular motion.     

单分子光子源信号背景比的研究

通过在不同信号背景比下的最佳信号噪声比分析,讨论单分子光子源背景信号分别为时间均匀分布和指数特性分布时同步取样时间的选取.在Hanbury-Brown-Twiss探测方式下,测量光子源的单事件光子统计概率P(n,n=0、1、2).研究给出在P(1)2P(2)-3P(2)时,直接测量单分子光子源的信号背景比的方法SBR=[P(1)]2/2P(2).当信号背景比SBR>2.41时研究给出判别单分子的方法P(2)<(2-4-2n-)2/2,n为每个激发周期内探测到的平均光子数.     

Correlation between double and nonresonant single ionization

We performed simultaneous measurements of electrons and ions produced in Xe photoionization driven by an 800-nm, 100-fs laser pulse. The obtained energy and angular resolved electron spectra allow the identification of the electronic states populated during the ionization. Xe2+ ions appear at the same laser intensity as electrons emerging from a nonresonant 9-photon ionization process of Xe. Similar to optical tunneling ionization, the nonresonant ionization delivers low-energy electrons needed for the formation of Xe2+ by a backscattering process.     

Observation of direct dissociative ionization in molecular hydrogen

Direct dissociative ionization is the simplest three-body breakup process in H2. We describe the experimental verification of direct dissociative ionization to the repulsive A2Sigma(+)(u) state by resolving the kinetic energy and angular distributions of the formed protons. A (2+1) resonant enhanced multiphoton ionization process via the isotropic E,F (1)Sigma(+)(g)(v = 6,J = 0) level is employed. The structure in the kinetic energy spectrum is well described by a projection of the vibrational wave function of the E,F (1)Sigma(+)(g)(v = 6,J = 0) state onto the repulsive ionic state. The electronic character of the ionization continuum is revealed by the proton angular distribution.     

Electron impact single and double ionization of magnesium

Electron impact single and double ionization cross-sections for magnesium have been calculated in the binary encounter model using accurate expression for (cross-section for energy transfer ΔE) as given by Vriens. Hartree-Fock velocity distributions for the target electrons have been used throughout the calculations. In case of double ionization contributions of inner shell ionization and Auger emission have been included in the present work. The results obtained in case of single ionization are excellent and at the same time the double ionization cross-sections show reasonably good agreement with the recent experimental observations. Substantiation of the viewpoint of Peach, and Boivin and Srivastava that a vacancy in the 2p shell of magnesium leads to double ionization is a remarkable feature of the present investigation. Received 9 October 2001 / Received in final form 8 January 2002 Published online 28 June 2002     

Electron impact single and double ionization of halogens

The binary encounter approximation has been used for calculations of electron impact single ionization cross-sections for F, Cl, Br and I and double ionization cross-sections for Br and I. Contributions of ionization from inner shells have also been included in the calculations. Hartree-Fock momentum distribution has been used for the bound electron as far as possible. The results have been found to be in satisfactory agreement with experimental observations.     

Electron impact single and double ionization of argon

Stable two-mode, and three-mode oscillations due to the spatial hole burning effect were observed experimentally with the increase of the pump power ratio in a laser-diode pumped sub-nanosecond microchip Cr,Yb:YAG self-Q-switched multimode laser. The stability of the output pulse trains was attributed to the mode coupling through antiphase dynamics between different modes. Modified multimode rate equations including the spatial hole-burning effect in the active medium and the non-linear absorption of the saturable absorber were proposed. Numerical simulations of the antiphase dynamics of such a laser were in good agreement with the experimental data, and the antiphase dynamics were explained by the evolution of the inversion population and the bleaching and recovery of the inversion population of the saturable absorber.     

飞秒强激光场中分子双电离的半经典动力学模拟

文章介绍了超短强激光场中原子、分子双电离的研究现状,提出了能够有效处理双电离过程的半经典模型,成功地重现了双电离率随激光强度变化的实验数据,同时预言了分子取向对双电离率的重要影响.文章还通过分析典型的双电离轨道的演化,给出了理解双电离复杂动力学过程的直观物理图像.     

Multiple ionization bursts in laser-driven hydrogen molecular ion

Theoretical study on H2(+) in an intense infrared laser field on the attosecond time scale reveals that the molecular ion shows multiple bursts of ionization within a half-cycle of the laser field oscillation, in contrast to the widely accepted tunnel ionization picture for an atom. These bursts are found to be induced by transient localization of the electron at one of the nuclei, and a relation between the time instants of the localization and the vector potential of the laser light is derived. A scheme is proposed to probe the localization dynamics by an extreme ultraviolet laser pulse.     

First-order photon interference of a single photon from a single quantum dot

Photon interference indicating wave-like nature of a single photon emitted from a single quantum dot is demonstrated. Photon state as a superposition of two orthogonal linear polarization modes is prepared inside a solid-state single photon source, which causes the first-order interference analogous to the Young’s double slit experiment. The lack of which-mode information is essential for observing the single photon interference.     

Estimating the ionization time of a hydrogen atom during its motion in a carbon nanotube

The processes in a hydrogen atom moving at a certain velocity along a row of atoms in a carbon nanotube are considered. The change in the atomic state is calculated by numerically solving the nonstationary Schr?dinger equation. The ionization time of the atom is estimated.     

Controlling attosecond double ionization dynamics via molecular alignment

We investigate the dynamics of double ionization in aligned nitrogen molecules. An ultrashort, weak laser pulse creates an aligned ensemble of molecules that is ionized with a subsequent, strong probe pulse. We find that the two electrons involved in nonsequential double ionization more likely exit the molecule in the same direction if it is parallel to the probe laser polarization, indicating that they are ejected within a few hundred attoseconds of each other. Double ionization is less probable and takes longer for perpendicular molecules.     

Electron dynamics of molecular frustrated double ionization driven by strong laser fields

We theoretically investigate the frustrated double ionization(FDI) of molecules with different alignment-dependence using a three-dimensional classical ensemble method. The numerical results show that the FDI probability decreases with increasing wavelength, which is similar to the wavelength dependence of the FDI probability of atoms. Tracing the classical trajectories reveals that the contributions to molecular FDI from single-recollision and multiple-recollision mechanisms are equal in the sh...     

Nonsequential double ionization of the aligned hydrogen molecule in strong field

This paper studies the nonsequential double ionization(NSDI) process of diatomic molecules aligned parallel and perpendicular to an intense linearly polarized laser field by using a three-dimensional semiclassical model.With this model,it achieves insight into the ion momentum distribution under the combined influence of a two-centre Coulomb potential and an intense laser field,and this result shows the significant influence of molecular alignment on the ratio between double and single ionization rate.Careful investigations show that the NSDI process for different alignment molecules has a close relation to the laser intensity and the different bounding electron distribution has a significant influence on the final ion momentum distribution.     

Comparison study of atomic and molecular single ionization in the multiphoton ionization regime

In this Letter, we report, for the first time in the multiphoton ionization regime, a comparison study of single-electron ionization of diatomic molecules versus rare gas atoms with virtually the same ionization potentials. In comparing N2+ to Ar+, a higher ion signal is seen in N2+ compared to Ar+ for linear polarization but the difference vanishes in circularly polarized light. In comparing O2+ to Xe+, we observe a suppression in O2+ compared to Xe+ for both linear and circular polarization but this suppression exhibits an intensity dependence; i.e., there is little suppression for O2+ at the lowest intensity range, but the suppression becomes increasingly stronger as the laser intensity increases. The multielectron screening model is used to discuss possible mechanisms of this intensity dependent suppression in O2+ in the multiphoton ionization regime.