Lithium ionization by a strong laser field

We study ab initio computations of the interaction of lithium with a strong laser field. Numerical solutions of the time-dependent fully correlated three-particle Schrodinger equation restricted to the one-dimensional soft-core approximation are presented. Our results show a clear transition from nonsequential to sequential double ionization for increasing intensities. Nonsequential double ionization is found to be sensitive to the spin configuration of the ionized pair. This asymmetry, also found in experiments of photoionization of Li with synchrotron radiation, shows evidence of the influence of the exclusion principle on the underlying rescattering mechanism.     

Electron-electron momentum exchange in strong field double ionization

We have investigated the momentum balance between the two electrons from strong field double ionization of argon at 780 nm and 1.9 x 10(14) W/cm(2). Experimental data show that perpendicular to the laser polarization direction the electrons emerge preferentially in opposite directions. Results of model calculations are found to agree well with the data and reveal a dominant role of the Coulomb correlation between the two outgoing electrons in this kinematical geometry. Differences between the experimental observations and the theoretical results for the ion momentum distribution indicate the importance of the further effects during the three-body breakup.     

Single-photon double ionization of an atom in a strong radiation field

Double ionization is studied by direct numerical integration of the time-dependent Schrödinger equation for a model two-electron system in the field of an electromagnetic wave in the case when the photon energy exceeds the energy required for the removal of both electrons of the atom. The probabilities of single-electron and double ionization are obtained as functions of the radiation intensity. The energy spectra and double pulse distributions of photoelectrons are analyzed. It is shown that single-photon ionization plays a significant role only in the limiting cases of weak and strong fields. The obtained results are used in an analysis of the contributions from different channels to the double-ionization process (in particular, for clarifying the role of the electron-electron interaction). The results of numerical calculations are compared with the analytic model of the phenomenon.     

Time-resolved quantum dynamics of double ionization in strong laser fields

Quantum calculations of a (1+1)-dimensional model for double ionization in strong laser fields are used to trace the time evolution from the ground state through ionization and rescattering to the two-electron escape. The subspace of symmetric escape, a prime characteristic of nonsequential double ionization, remains accessible by a judicious choice of 1D coordinates for the electrons. The time-resolved ionization fluxes show the onset of single and double ionization, the sequence of events during the pulse, and the influences of pulse duration and reveal the relative importance of sequential and nonsequential double ionization, even when ionization takes place during the same field cycle.     

The above-threshold ionization spectrum in a strong linearly polarized laser field

We use the saddle-point method to derive analytical expressions for the spectral-angular probability distributions of the ionization by a strong linearly polarized laser field in Keldysh’s model that are valid for an arbitrary electron energy and adiabaticity parameter. We obtain asymptotic expansions of the general formulas in the multiphoton and tunneling regimes, analyze their accuracy, and formulate the validity conditions. We provide literal estimates of the parameters that characterize the properties and evolution of the distributions.     

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.     

Binary and recoil collisions in strong field double ionization of helium

We have investigated the correlated momentum distribution of both electrons from nonsequential double ionization of helium in a 800 nm, 4.5 x 10(14 W/cm2 laser field. Using very high resolution coincidence techniques, we find a so-far unobserved fingerlike structure in the correlated electron momentum distribution. The structure can be interpreted as a signature of the microscopic dynamics in the recollision process. We identify features corresponding to the binary and recoil lobe in field-free (e,2e) collisions. This interpretation is supported by analyzing ab initio solutions of a fully correlated three-dimensional helium model.     

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.     

Relativistic theory of tunnel and multiphoton ionization of atoms in a strong laser field

Relativistic generalization is developed for the semiclassical theory of tunnel and multiphoton ionization of atoms and ions in the field of an intense electromagnetic wave (Keldysh theory). The cases of linear, circular, and elliptic polarizations of radiation are considered. For arbitrary values of the adiabaticity parameter γ, the exponential factor in the ionization rate for a relativistic bound state is calculated. For low-frequency laser radiation , an asymptotically exact formula for the tunnel ionization rate for the atomic s level is obtained including the Coulomb, spin, and adiabatic corrections and the preexponential factor. The ionization rate for the ground level of a hydrogen-like atom (ion) with Z ? 100 is calculated as a function of the laser radiation intensity. The range of applicability is determined for nonrelativistic ionization theory. The imaginary time method is used in the calculations.     

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...     

Tunneling ionization of air in the strong field of femtosecond laser pulses

The effect of the tunneling ionization of air excited by individual intense femtosecond pulses with subcritical peak powers has been investigated by the optoacoustic method. With an increase in the laser radiation intensity in the range of 0.5–20 PW/cm², the saturation of the amplitude of acoustic pressure with the corresponding decrease in the nonlinearity index of this dependence is observed. The analysis of the ionization of air molecules in the Ammosov-Delone-Krainov model of tunneling ionization predicts a weakly nonlinear increase and saturation of the yield of singly charged ions at an air ionization degree close to 50% under these conditions of the effect of femtosecond laser radiation.     

Bremsstrahlung in a strong laser field

We consider the bremsstrahlung of electrons as they collide with ions in a strong laser field. The bremsstrahlung spectrum has been found to be enriched in sufficiently strong fields. Particular attention is given to the coherent bremsstrahlung component. We propose a qualitative model that explains our results. The possibility of experimentally observing the coherent bremsstrahlung component in a strong field is discussed.     

飞秒激光惰性气体Ar原子多次电离过程的空间分辨研究

使用100飞秒、1014 W/cm2的强激光与惰性气体Ar原子相互作用,我们利用飞行时间质谱仪结合Z扫描技术获得了各次电离的Ar原子在激光焦点附近不同位置处强度分布.测量得到的各个不同电离态Ar n+(n=1～4)的产额随激光焦点位置变化关系与不同电离态的空间分布理论预言相一致.     

Lorentz ionization of atoms in a strong magnetic field

Lorentz ionization emerges due to the motion of atoms or ions in a strong magnetic field. We use the semiclassical approximation to calculate the probability w _L of Lorentz ionization. We also find the stabilization factor S, which takes into account the reduction by the magnetic field of the probability of ionization decay of the bound s state. We estimate the probabilities w _L in magnetic-cumulation experiments and in astrophysics. We also qualitatively examine the dynamics of the magnetic cumulation process with allowance for the conductivity of the shell. Finally, we discuss a paradox related to the use of the quasistationary solution at the shell expansion stage. Zh. éksp. Teor. Fiz. 115, 1642–1663 (May 1999)     

Recoil-Ion momentum distributions for single and double ionization of helium in strong laser fields

We have measured the momentum distributions of singly and doubly charged helium ions created in the focus of 220 fs, 800 nm laser pulses at intensities of (2.9-6.6)x10(14) W/cm(2). All ions are emitted strongly aligned along the direction of polarization of the light. We find the typical momenta of the He2+ ions to be 5-10 times larger than those of the He1+ ions and a two peak structure at the highest intensity.     

Trap ionization in phosphors in a strong electric field

Temperature dependences of the intensity of Gudden-Pohl flashes in zinc sulfide crystals in various electric fields were measured in order to study trap ionization by electric fields. The decrease in the flash intensity from trap levels of a given depth in a certain temperature range is due to a decrease in the probability for the liberation of an electron from a trap as the temperature decreases. The temperature dependences of the flash intensity found in various electric fields are compared with the theoretical temperature dependence of the probability for electron liberation from a trap. The agreement between experimental and theoretical curves indicates that electrons are liberated from the deeper levels through ionization by an electric field involving many phonons.Translated from Izvestiya VUZ. Fizika, No. 10, pp. 53–58, October, 1969.     

Multiple recapture of electrons in multiple ionization of the argon dimer by a strong laser field

We observe multiply frustrated tunneling ionization-induced dissociation of the argon dimers by intense linearly polarized ultrashort laser pulses. By measuring the kinetic energy release and angular distribution of the Coulomb explosion of up to eightfold ionized argon dimers, we can trace the recapture of up to two electrons to Rydberg states of the highly charged compound at the end of the laser pulse. Upon dissociation of the dimer, the Rydberg electron prefers to localize at the atomic ion with the higher charge state. We probe the electron recapture dynamics by a time-delayed weak pulse.