Giant resonances of endohedral atoms

It is demonstrated for the first time that the effect of a fullerene shell on the photoionization of a “caged” atom in an endohedral can result in the formation of giant endohedral resonances or GER. This is illustrated by the concrete case of the Xe@C₆₀ photoionization cross section that, at 17 eV, exhibits a powerful resonance with total oscillator strengths of about 25. The prominent modification of the 5p ⁶ electron photoionization cross section of Xe@C₆₀ takes place due to the strong fullerene shell polarization under the action of the incoming electromagnetic wave and the oscillation of this cross section due to the reflection of the photoelectron from Xe by the C₆₀. These two factors transform the smoothly decreasing 5p ⁶ cross section of Xe into a rather complex curve with a powerful maximum for Xe@C₆₀, with the oscillator strength of it being equal to 25. We also present the results for the dipole angular anisotropy parameter that is strongly affected by the reflection of the photoelectron waves, but not modified by C₆₀ polarization. The text was submitted by the authors in English.     

Photoionization of the outer electrons in noble gas endohedral atoms

We suggest a prominent modification of the outer shell photoionization cross section in noble gas (NG) endohedral atoms NG@C _n under the action of the electron shell of fullerene C _n . This shell leads to two important effects: a strong enhancement of the cross section due to fullerene shell polarization under the action of the incoming electromagnetic wave and to prominent oscillation of this cross section due to the reflection of a photoelectron from the NG by the fullerene shell. Both factors lead to powerful maxima in the outer shell ionization cross sections of NG@C _n , which we call giant endohedral resonances. The oscillator strength reaches a very large value in the atomic scale, 25. We consider atoms of all noble gases except He. The polarization of the fullerene shell is expressed in terms of the total photoabsorption cross section of the fullerene. The photoelectron reflection is taken into account in the framework of the so-called bubble potential, which is a spherical δ-type potential. It is assumed in the derivations that the NG is centrally located in the fullerene. It is also assumed, in accordance with the existing experimental data, that the fullerene radius R _C is much larger than the atomic radius r _A and the thickness Δ_C of the fullerene shell. As was demonstrated recently, these assumptions allow us to represent the NG@C _n photoionization cross section as a product of the NG cross section and two well-defined calculated factors. The text was submitted by the authors in English.     

Interference effects in photoionization of noble gas atoms outer s-subshells

A strong influence of ns²np⁶ → ns²np⁵ εd transition on the outer ns subshell photoionization cross section of noble gas atomsis demonstrated.     

On nonlinear cascades and resonances in the outer magnetosphere

The paper addresses nonlinear phenomena that control the interaction between plasma flow (solar wind) and magnetic barrier (magnetosphere). For the first time we demonstrate that the dominant solar wind kinetic energy: (i) excites boundary resonances and their harmonics which modulate plasma jets under the bow shock; (ii) produces discrete three-wave cascades, which could merge into a turbulent-like one; (iii) jet produced cascades provide the effective anomalous plasma transport inside and out of the magnetosphere; (iv) intermittency and multifractality characteristics for the statistic properties of jets result in a super-ballistic turbulent transport regime. Our results could be considered as suggestive for the space weather predictions, for turbulent cascades in different media and for the laboratory plasma confinement (e.g., for fusion devices).     

Distortion and preservation of giant resonances in endohedral atoms A@C<Subscript>60</Subscript>

It is demonstrated in this Letter that the effect of the fullerene shell upon atomic Giant resonance decisively depends upon energy of photoelectrons, by which the resonance decay. According to the earlier prediction, the Giant resonance in Xe is strongly modified in the endohedral Xe@C₆₀ being transformed from a single broad and powerful maximum in Xe into four quite narrow, but with almost the same total oscillator strength. On the contrary, here the 4d Giant resonances in ions Ce³⁺ (the electronic structure that Ce has, when stuffed into fullerene), in Ce⁴⁺, and Eu are considered. In none of them the 4d Giant resonance in endohedrals is affected essentially. This is because the decay of the Giant resonances in these endohedrals proceeds by emission of fast photoelectrons that are almost unaffected by the C₆₀ shell. The results obtained give at least qualitative explanation to the fact that relatively recent observation of 4d Giant resonance in Ce@C₈₂⁺, where the Giant resonance was observed as a maximum without noticeable structure. The article is published in the original.     

Evaluation of the probability of hydrogen atoms photoionization in a strong ultrashort laser field using the trajectory method

A method for calculating transition probabilities based on an earlier developed trajectory approach is tested by the example of evaluating the probability of photoionization of the hydrogen atom exposed an ultrashort optical pulse.     

碱金属原子的光激发与光电离

本文研究了碱金属原子在三步激光脉冲作用下的光激发和光电离过程的动力学特性, 重点关注和比较了锂和铯原子的异同. 针对多种激发模式, 本文不但建立了其原子布居数在各个跃迁态的速率方程组, 还给出了各相关态的光激发和光电离过程的解析解. 通过精心设计并选择了特殊情况, 显著简化了解析解的数学表达式, 从而凸显和讨论了其物理内涵. 通过自行编程, 系统地计算和观察了各种激发模式对锂原子的光激发和光电离过程的可能影响, 研究和讨论了电离率随激光参数的变化规律. 在相同激发模式下, 比较和分析了采用两种不同激发路径所导致的各态原子布居率的变化, 凸显了改变原子参数所产生的作用. 探讨了锂和铯原子在类似的激发条件下在电离率方面的差别. 最后, 基于本文的研究结果, 本文指出了优化电离率的多种途径.     

Nonlinear resonances of contact photoionization in heterogeneous nanostructures

A theory of nonlinear interference effects is constructed for a heterogeneous charge transfer between atoms in polycrystalline films or heterogeneous nanostructures of the semiconductor-insulator type, which interact with resonance radiation, and a metallic contact surface. The probability of resonance contact photoionization in heterogeneous solid nanostructures is determined, which makes it possible to use this process in nanotechnologies and nonlinear information systems. Nonlinear resonances of contact photoionization are asymmetric due to interference of a radiative transition to an excited state and a transition to the continuum induced by the metal surface. The probability of resonance contact photoionization abruptly decreases with increasing distance between an atom in the semiconductor and the metal.     

钴、钛原子激发态光电离研究

本文报道紫外区钛和钴原子共振增强多光子电离(REMPI)谱和激发态绝对光电离截面。实验上通过激光烧蚀金属样品制备中性原子,由飞行时间质谱仪检测离子产物,在298-351nm范围扫描激光波长,得到钛原子和钴原子共振增强多光子电离谱;并根据共振离子信号强度与电离激光通量关系得到原子激发态的绝对光电离截面,这些激发态电离截面的实验值在0.5-4 Mb。     

On the absence of a density effect for inner shell ionization

It is shown that the observed absence of a density effect in inner shell ionization in solids is due to the fact that the required momentum transfer has a wavelength of the order of, or smaller than, the lattice constant, and thus cannot be transmitted to the lattice. This leads to a cut-off in the dielectric function corresponding to electronic binding energies above 1—1.5 keV, depending on the lattice constant. For more strongly bound electrons there shoul be no density effect.     

钴、钛原子激发态光电离研究

本文报道紫外区钛和钴原子共振增强多光子电离(REMPI)谱和激发态绝对光电离截面。实验上通过激光烧蚀金属样品制备中性原子,由飞行时间质谱仪检测离子产物,在298-351nm范围扫描激光波长,得到钛原子和钴原子共振增强多光子电离谱;并根据共振离子信号强度与电离激光通量关系得到原子激发态的绝对光电离截面,这些激发态电离截面的实验值在0.5-4 Mb。     

A note on the projectile charge dependence of inner shell ionisation of atoms by heavy charged particles

The formula for the binding of the electron to the impinging projectile in inner shell ionization of atoms by heavy charged particles in the static approximation, are generalized to arbitrary electron wavefunctions. The effect is calculated for K-shell electrons using relativistic wavefunctions. A qualitative difference in the impact parameter dependency of the effect between light and heavy target are found.     

Nonlinear resonances in the near-field interaction between atoms

It has been shown that nonlinear near-field optical resonances occur in diatomic nanostructures consisting of identical or different two-level atoms in the presence of a radiation field when the dipole-dipole interaction is taken into account. The frequencies of these resonances depend strongly on the intensity of the external optical radiation, on the initial conditions, on the polarization of the external field with respect to the axis of the nanostructure, and on the interatomic distance. The interatomic interaction is taken into account beyond perturbation theory. For this reason, the effective polarizabilities of the atoms of the nanostructure are expressed in terms of the polynomials of both the interatomic distance and the electric field strength of the external optical wave. A “falling tower” effect that is caused by the nonlinear behavior of the local dipole moments of atoms in the nanostructure is predicted.     

Scaling laws for the photoionization cross section of two-electron atoms

The cross sections for single-electron photoionization in two-electron atoms show fluctuations which decrease in amplitude when approaching the double-ionization threshold. Based on semiclassical closed orbit theory, we show that the algebraic decay of the fluctuations can be characterized in terms of a threshold law sigma proportional to |E|(mu) as E --> 0(-) with exponent mu obtained as a combination of stability exponents of the triple-collision singularity. It differs from Wannier's exponent dominating double-ionization processes. The details of the fluctuations are linked to a set of infinitely unstable classical orbits starting and ending in the nonregularizable triple collision. The findings are compared with quantum calculations for a model system, namely, collinear helium.     

The influence of inner shells upon the angular distribution of Kr 4p-photoelectrons

The influence of inner shells upon the anisotropy parameter of the 4p-photoelectrons angular distribution in Kr is investigated in the frame of the random phase approximation with exchange (RPAE). The comparison with experimental data and other calculations demonstrates an essential role of intershell correlations, the account of which allows to achieve a satisfactory agreement between theoretical and experimental data.