Inelastic scattering of broadband electron wave packets driven by an intense midinfrared laser field

Intense, 100 fs laser pulses at 3.2 and 3.6 μm are used to generate, by multiphoton ionization, broadband wave packets with up to 400 eV of kinetic energy and charge states up to Xe(+6). The multiple ionization pathways are well described by a white electron wave packet and field-free inelastic cross sections, averaged over the intensity-dependent energy distribution for (e, ne) electron impact ionization. The analysis also suggests a contribution from a 4d core excitation, or giant resonance, in xenon.     

Redshift in the optical absorption of ZnO single crystals in the presence of an intense midinfrared laser field

We report time-resolved electroabsorption of a weak probe in a 500 μm thick zinc-oxide crystal in the presence of a strong midinfrared pump in the tunneling limit. We observe a substantial redshift in the absorption edge that scales with the cube root of intensity up to 1 TW/cm(2) (0.38 eV cm(2/3) TW(-1/3)) after which it increases more slowly to 0.4 eV at a maximum applied intensity of 5 TW/cm(2). The maximum shift corresponds to more than 10% of the band gap. The change in scaling occurs in a regime of nonperturbative high-order harmonic generation where electrons undergo periodic Bragg scattering from the Brillouin zone boundaries. It also coincides with the limit where the electric field becomes comparable to the ratio of the band gap to the lattice spacing.     

氦原子在啁啾激光与中红外组合场中产生的单个阿秒脉冲

通过Crank Nicolson方法数值求解一维氦原子的含时Schrdinger方程,研究了啁啾激光与中红外激光形成组合场驱动氦原子发射高次谐波的特点.研究结果表明,在组合场驱动下,高次谐波平台区能得到很大的扩展,其截至位置得到大幅度扩展,对平台区不同阶次范围的高次谐波进行叠加均能得到单个的阿秒脉冲,最短可实现46 as的单个脉冲输出,经分析发现,中红外场的加入,不仅使高次谐波的平台得到扩展,而且提高了平台区前端的谐波强度.通过经典计算和对电离几率特点的讨论,解释了发生这种现象的原因.     

Scaling laws of electron acceleration driven by an intense laser pulse

We studied the scaling laws for slow-electron acceleration driven by an intense laser pulse in a vacuum, the ponderomotive acceleration scenario (PAS) scheme. With 3D test particle simulation by numerically solving the relativistic Lorentz–Newton equation of motion, the maximum electron energy gain was found to be proportional to the laser intensity (a₀), the laser beam width (w₀), and inversely proportional to the laser pulse duration (τ). Theoretical analyses and a physical explanation based on the ponderomotive potential model (PPM) are presented. PACS 42.50.Vk; 41.75.Jv; 42.60.Jf     

Ionization in an intense field considering Coulomb correction

We derive a simple ionization rate formula for the ground state of a hydrogen atom in the velocity gauge under the conditions:ω1 a.u.(a.u.is short for atomic unit) and γ1(ω is the laser frequency and y is the Keldysh parameter).Comparisons are made among the different versions of the Keldysh-Faisal-Reiss(KFR) theory.The numerical study shows that with considering the quasi-classical(WKB) Coulomb correction in the final state of the ionized electron,the photoionization rate is enhanced compared with without considering the Coulomb correction,and the Reiss theory with the WKB Coulomb correction gives the correct result in the tunneling regime.Our concise formula of the ionization rate may provide an insight into the ionization mechanism for the ground state of a hydrogen atom.     

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.     

β-Decay of an unpolarized neutron in an intense electromagnetic field

This study will consider the effect of a circularly polarized electromagnetic field on- decay of a neutron for values of the parameter ea/m 1 and ea/m 1, where e and m are the charge and mass of the electron; anda is the amplitude of the field potential. Within the framework of the V=A variant of the weak interaction theory, in the first-order perturbation theory, it is shown that with increase in field intensity the probability of neutron decay increases. The energy distributions of the electrons generated are calculated for ea/m = 0.5 and ea/m=1, and the results obtained are evaluated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 115–120, April, 1974.The author thanks S. V. Izmailov and R. Yu. Volkovyskii for their evaluation of the study.     

Delocalization and wave-packet dynamics in one-dimensional diluted Anderson models

We study the nature of one-electron eigen-states in a one-dimensional diluted Anderson model where every Anderson impurity is diluted by a periodic function f(l). Using renormalization group and transfer matrix techniques, we provide accurate estimates of the extended states which appear in this model, whose number depends on the symmetry of the diluting function f(l). The density of states (DOS) for this model is also numerically obtained and its main features are related to the symmetries of the diluting function f(l). Further, we show that the emergence of extended states promotes a sub-diffusive spread of an initially localized wave-packet.Received: 7 July 2003, Published online: 19 November 2003PACS: 63.50. + x Vibrational states in disordered systems - 63.22. + m Phonons or vibrational states in low-dimensional structures and nanoscale materials - 62.30. + d Mechanical and elastic waves; vibrations     

Quantum processes in an intense electromagnetic field. I

The Furry approach for arbitrary external electromagnetic fields that do not generate real pairs is considered. Problems of the existence of a stable vacuum in the field are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 81–86, October, 1976.The author is grateful to F. A. Berezin for refinement of the theorems used in this work and to A. A. Grib, S. G. Mamaev, and V. M. Mostepanenko for valuable critical comments.     

Quantum processes in an intense electromagnetic field. II

An approach is suggested to the treatment of processes in an external electromagnetic field that generates real pairs. The interaction with the field is allowed for exactly by means of the solutions of the Dirac equation. Processes of arbitrary order in the electron-photon interaction are considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 86–92, October, 1976.In conclusion the author wishes to thank V. G. Bagrov and Sh. M. Shvartsman for useful discussions and critical comments.     

The ionization of atoms in an intense nonclassical electromagnetic field

The ionization of atoms in a strong nonclassical unimodal electromagnetic field was considered. It was shown that the probability of ionization could substantially change depending on the quantum state of the field even at a constant mean number of quanta in the radiation mode. The difference of ionization rates was especially large for multiphoton ionization processes. It was, in particular, shown that a nonclassical field could be much more effective from the point of view of the ionization of atoms than a classical field of the same intensity. The characteristics of the decay of a bound atomic system state in a strong nonclassical field were studied without invoking perturbation theory.     

Inverse-bremsstrahlung absorption of an intense laser field in cluster plasma

Inverse-bremsstrahlung absorption of an intense laser field in cluster plasma is considered in the Born approximation with allowance made for electron interaction with the entire subsystem of clustered ions. The electromagnetic power absorbed in plasma is calculated for linearly and circularly polarized laser radiations. It is shown that plasma “clustering” can give rise to much more effective absorption of electromagnetic energy as a result of collisions. The collective effects (the action of the overall field of clustered ions on an electron) dominate over the elementary processes (electron scattering by individual ions in the cluster) in the course of inverse bremsstrahlung.     

Dynamics of a spherical particle in an intense optical field

The evaporation rate of a spherical particle in an intense, isotropic optical field is calculated.     

Electron scattering in the presence of an intense electromagnetic field

The general theory of electron scattering in the presence of an external electromagnetic field, provided by an intense laser beam, accompanied by absorption ofn photons, each with energy ?ω is discussed. The calculation leads to many summations over intermediate states. A general method for exactly evaluating several sums is described in detail. Numerical results show that the cross-section varies with intensity in a power law fashion.     

Coherent control of rotational wave-packet dynamics via fractional revivals

We show (i) how the evolution of a wave packet created from an initial thermal ensemble can be controlled by manipulating interferences during the wave packet's fractional revivals and (ii) how the wave-packet evolution can be mapped onto the dynamics of a few-state system, where the number of states is determined by the amount of information one wants to track about the wave packet in the phase space. We illustrate our approach by (i) switching off and on field-free molecular axis alignment induced by a strong laser pulse and (ii) converting alignment into field-free orientation, starting with rotationally cold or hot systems.     

Scattering by a potential well in an intense radiation field

Scattering by a spherically symmetric potential well in a laser radiation field is examined in the eikonal approximation. The total scattering cross section is found for radiation of an arbitrary number of photons. The range of values of the Born parameter is obtained for which the influence of the radiation field on the scattering cross sections is significant.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 73–76, April, 1989.