Double ionization by strong elliptically polarized laser pulses

We join the tribute to Professor N.B. Delone in this memorial issue by presenting the results of new calculations on the effects of ellipticity on double ionization by short and strong near-optical laser pulses.     

两束短脉冲激光驱动O_2分子的取向特性

利用数值方法模拟O2分子在短脉冲激光场中的转动波包,从理论上研究了在两束短脉冲激光驱动下O2分子的取向程度.在相同的环境温度下,与单脉冲激光驱动相比,通过优化两束激光脉冲的强度比和时间延迟,可以有效提高O2分子的取向程度.研究表明,当两束激光脉冲的强度比约为1:3,时间延迟为11.73 ps时,O2分子可以达到很好的取向效果.     

Trident pair production in strong laser pulses

We calculate the trident pair production amplitude in a strong laser background. We allow for finite pulse durations, while still treating the laser fields nonperturbatively in strong-field QED. Our approach reveals explicitly the individual contributions of the one-step and two-step processes. We also expose the role gauge invariance plays in the amplitudes and discuss the relation between our results and the optical theorem.     

Coherent crystallization of bismuth under strong excitation by ultrashort laser pulses

By means of coherent control, fully symmetric bismuth phonons A _1og are investigated at helium temperature depending on the degree of crystal excitation. It is shown that coherent phonons with large amplitude show phase rigidity that is absent at small amplitude. Such a change in the phase properties of crystal lattice excitations can be understood using the concept of a coherent crystal, the achievement of which results from condensation of phonon modes arising with increasing degree of excitation.     

Ionization of clusters in strong x-ray laser pulses

The effect of intense x-ray laser interaction on argon clusters is studied theoretically with a mixed quantum/classical approach. In comparison to a single atom we find that ionization of the cluster is suppressed, which is in striking contrast to the observed behavior of rare-gas clusters in intense optical laser pulses. We have identified two effects responsible for this phenomenon: A high space charge of the cluster in combination with a small quiver amplitude and delocalization of electrons in the cluster. We elucidate their impact for different field strengths and cluster sizes.     

Numerical study on transmission of multimode laser pulses by dye molecules

A theoretical model and a numerical study of the transmission of multimode laser pulses by malachite green dye are presented. Excited state absorption is taken into account. The transmitted pulses exhibit increased intensity fluctuations moderated by the excited state absorption. Reference is made to recent experimental results.     

Field-free two-direction alignment alternation of linear molecules by elliptic laser pulses

We show that a linear molecule subjected to a short specific elliptically polarized laser field yields post-pulse revivals exhibiting alignment alternatively located along the orthogonal axis and the major axis of the ellipse. The effect is experimentally demonstrated by measuring the optical Kerr effect along two different axes. The conditions ensuring an optimal field-free alternation of high alignments along both directions are derived.     

Nonsequential double ionization of diatomic molecules by elliptically polarized laser pulses

Using the classical ensemble method, we investigate nonsequential double ionization （NSDI） of diatomic molecules by elliptically polarized laser pulses. The results show that the ellipticity of the laser field has a strong suppression effect on NSDI probabilities both in parallel and perpendicular alignments. The double ionization （DI） channel is commonly dominated by NSDI, and the NSDI channel changes with ellipticity. As ellipticity increases, more and more NSDIs occur through recollision excitation with subsequent field ionization （RESI）. Moreover, like the case of linear polarization, the two electrons involved in NSDI for perpendicularly aligned molecules are more likely to emit into the opposite hemispheres as compared to the case of parallel alignment. Additionally, this alignment effect increases as ellipticity increases.     

Long plasma channels and high-voltage discharges induced by strong picosecond laser pulses

The formation of long plasma channels and laser-induced high-voltage discharges are demonstrated by focusing infrared picosecond laser pulses in air. Based on measurements of the channel conductivity, the maximum electron density in excess of 1014cm-3is estimated. The plasma channels are good conductors, through which long-air-gap high-voltage discharges are triggered. The breakdown voltages show large drops but the discharging paths are not well guided: in this, the plasma spots distributed along the channel might play an important role.     

飞秒强激光场中的原子、分子——非微扰现象研究

文章简要回顾了飞秒强激光场中的原子、分子这一研究领域在近年来所取得的一系列里程碑式的重大发现,包括多光子电离、阈上电离、隧穿电离、越垒电离、非顺序双电离、电离稳定化、高次谐波发射等等非微扰现象.讨论了纯量子理论和纯经典方法在处理该类问题时经常遇到的困难.介绍了作者所在小组为此提出的半经典模型及其在解释强场物理现象时所取得的成果.最后对这一领域在未来几年内的可能发展方向作了简单的评述.     

Triple-ionization-induced dissociation of molecules in strong laser fields

We study triple-ionization-induced dissociation in diatomic molecules with different laser polarizations.     

强激光场中团簇Na_2的谐波产生

在时间相关的局域密度近似TDLDA理论框架下 ,研究了强激光场中最简单金属团簇Na2 高次谐波的产生。当激光参数选为强度 1.338× 10 12 W/cm2 和频率 5 .2 6 6eV时 ,在激光频率和Na2 的共振频率处成峰 ;而当强度为 5 .0 5 5× 10 12 W/cm2 ,频率为 1.12 4eV时 ,观察到了第三 ,第五次谐波产生。     

Numerical investigation of atomic dynamics in strong ultrashort laser pulses

The algorithms for the numerical solution of the stationary and nonstationary Schrödinger equations that allow the analysis of the dynamics of single-electron atoms in the presence of an external strong linearly polarized electromagnetic field in the dipole approximation are presented. Several examples of the simulation of atomic dynamics in the presence of high-intensity laser fields are considered to illustrate the possibilities of the proposed algorithms.     

强激光场中团簇Na2的谐波产生

在时间相关的局域密度近似TDLDA理论框架下,研究了强激光场中最简单金属团簇Na2高次谐波的产生.当激光参数选为强度1.338×1012W/cm2和频率5.266eV时,在激光频率和Na2的共振频率处成峰;而当强度为5.055×1012W/cm2,频率为1.124eV时,观察到了第三,第五次谐波产生.     

低强度周期量级脉冲驱动排列分子的非次序双电离

本文利用三维经典系综模型研究了低强度周期量级脉冲驱动排列分子的非次序双电离. 结果表明, 电子对的关联特性强烈地依赖于分子的排列方向和激光脉冲的载波包络相位; 垂直分子反关联电子对的比例总是高于平行分子反关联电子对的比例; 当载波包络相位从0到π 逐渐增加时, 反关联电子对的数目先增加再减少; 对于平行分子, 电子对的释放总是以正关联为主; 而垂直分子的主导关联模式则依赖于激光脉冲的载波包络相位, 当载波包络相位为0.3π-0.7π之间时, 电子对以反关联释放为主, 其他相位下以正关联为主. 本文利用分子势能曲线和电子返回能量很好地解释了电子关联特性对分子排列方向和载波包络相位的依赖关系.     

Above threshold Coulomb explosion of molecules in intense laser pulses

We have measured and explained a new mechanism of molecular ionization near the appearance intensity that produces a sequence of peaks in the nuclear kinetic energy spectrum separated by the photon energy. Our interpretation is based on an internally consistent model for the nuclear motion during an intense laser pulse. Within this model, the same concepts and language can be used for both dissociation and ionization, leading to a more unified understanding of the dynamics.     

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.     

Internal collision double ionization of molecules driven by co-rotating two-color circularly polarized laser pulses

The double ionization process of molecules driven by co-rotating two-color circularly polarized fields is investigated with a three-dimensional classical ensemble model. Numerical results indicate that a considerable part of the sequential double ionization(DI) events of molecules occur through internal collision double ionization(ICD), and the ICD recollision mechanism is significantly different from that in non-sequential double ionization(NSDI). By analyzing the results of internuclear distan...