Inelastic processes and the reemission of attosecond and shorter electromagnetic pulses at the interaction with atoms

Inelastic processes and the reemission of attosecond and shorter electromagnetic pulses by atoms have been considered within the analytical solution of the Schrödinger equation in the sudden perturbation approximation. A method of calculations with the exact inclusion of spatial inhomogeneity of the field of an ultrashort pulse and the momenta of photons in the reemission processes has been developed. The results have been presented in the form of analytical formulas. The probabilities of inelastic processes and spectra of reemission of ultrashort electromagnetic pulses by single-electron atoms have been calculated.     

Dynamics of electronic transitions and reemission spectra of attosecond electromagnetic pulses

The processes of reemission of attosecond electromagnetic pulses by systems in nonstationary states have been considered. The probabilities of the reemission of attosecond electromagnetic pulses at the resonance charge exchange of a proton on a hydrogen atom and at the decay of a quasistationary state, as well as the probabilities of the reemission of attosecond pulses by a system in a resonance external field, have been calculated as examples. The developed method can be applied to more complex targets, including targets in the collision state, and to various chemical reactions.     

Spectra for the reemission of attosecond and shorter electromagnetic pulses by multielectron atoms

Based on the analytical solution of the Schrödinger equation, we have considered the reemission of attosecond and shorter electromagnetic pulses by multielectron atoms in the sudden perturbation approximation. We have developed a technique of calculating the spectra for the reemission of attosecond and shorter electromagnetic pulses by neutral multielectron atoms with nuclear charges from 1 to 92. The results are presented in the form of analytical formulas dependent on several coefficients and screening parameters tabulated for all of the atoms whose electron densities are described by the well-known Dirac–Hartree–Fock–Slater model. As examples we have calculated the spectra for the reemission by lithium, carbon, calcium, and iron atoms for two types of incident pulse: Gaussian and “sombrero.”     

Reemission spectra and interference effects upon interaction of ultrashort electromagnetic pulses with nanosystems

The processes of reemission of ultrashort electromagnetic pulses by arbitrary nanosystems consisted of isolated complex atoms have been considered. The angular distributions of reemission spectra have been obtained for a series of regular nanosystems. It has been shown that the interference of the photon-emission amplitudes leads to the appearance of characteristic “diffraction” maxima. One-, two-, and three-dimensional nanostructures, as well as planar and cylindrical constructions as models of planar nanosystems and nanotubes, were used as examples that allow a simple analytical consideration.     

Inelastic processes and interference effects during the interaction of positronium with ultrashort electromagnetic pulses

The excitation, breakup, and reradiation during the interaction of a positronium atom with ultrashort electromagnetic pulses are considered. The probabilities of inelastic processes and reradiation spectra have been obtained. The interference between the amplitudes of the photon emission by the electron and positron is shown to contribute noticeably to the reradiation spectra. The developed approach is applicable for describing the interaction of positronium with ultrashort pulses of attosecond or shorter duration.     

Study of correlation effects during reemission of ultrashort electromagnetic pulses by the helium atom

The calculation of the energy of the ground state of atoms is the criterion for the correctness of compact analytical atomic wave functions. However, such a test is in fact static. We studied the degree of taking into account electron correlations in various simple analytical wave functions in the dynamic process of reemission by the helium atom of ultrashort pulses of an electromagnetic field. Direct guidelines are given on the use of particular analytical wave functions, which can be helpful in simple calculations and estimations of dynamic processes.     

Measurement of harmonic phase differences by interference of attosecond light pulses

By using a self-referencing technique, we have experimentally measured the influence of the carrier-envelope phase of femtosecond light pulses on the phase of the electric field of the radiation produced by high-order harmonic generation. We show that, in particular experimental conditions, the temporal evolution of the electric field of the attosecond pulses, is directly controlled by the carrier-envelope phase of the driving pulses.     

Interaction of attosecond electromagnetic pulses with atoms: The exactly solvable model

We consider the exactly solvable model of interaction of zero-duration electromagnetic pulses with an atom. The model has a number of peculiar properties which are outlined in the cases of a single pulse and two opposite pulses. In perspective, it can be useful in different fields of physics involving interaction of attosecond laser pulses with quantum systems. The text was submitted by the authors in English.     

Reemission spectra and interference effects at the interaction of multiatomic targets with ultrashort electromagnetic pulses

The processes of reemission of ultrashort electromagnetic pulses by linear chains consisting of isolated multielectron atoms have been considered. The developed method makes it possible to accurately take into account the spatial inhomogeneity of the field of an ultrashort pulse and the momenta of photons in reemission processes. The angular distributions of reemission spectra have been obtained for an arbitrary number of atoms in a chain. It has been shown that the interference of the photon emission amplitudes leads to the appearance of characteristic “diffraction” maxima. The results allow standard generalization to the cases of rescattering from two-dimensional (graphene-like) and three-dimensional lattices, as well as to the case of the inclusion of thermal vibrations of the atoms of lattices.     

Effect of nuclear motion on molecular high-order harmonics and on generation of attosecond pulses in intense laser pulses

We calculate harmonic spectra and shapes of attosecond-pulse trains using numerical solutions of Non-Born-Oppenheimer time-dependent Shr?dinger equation for 1D H2 molecules in an intense laser pulse. A very strong signature of nuclear motion is seen in the time profiles of high-order harmonics. In general the nuclear motion shortens the part of the attosecond-pulse train originating from the first electron contribution, but it may enhance the second electron contribution for longer pulses. The shape of time profiles of harmonics can thus be used for monitoring the nuclear motion.     

Generation of attosecond pulses in molecular nitrogen

We investigate the carrier-envelope phase dependence of the total ionization yield for single and double ionization of xenon. We compare our results to theoretical calculations and to the phase dependent asymmetry in photoelectron emission. We observe that the phase dependence of the photoion yields, regardless if single or double ionization, is at least 2-3 orders of magnitude below the photoelectron emission signal. We conclude that total photoionization yields are only very weakly dependent on the carrier envelope phase, and that they are not a useful means for measurement of the phase. It seems possible that the broad bandwidth of few-cycle pulses facilitates multiphoton ionization, which leads to a randomization of strong field ionization phase dependencies. Besides, we observe that the spatial asymmetry in photoelectron emission appears to be useful as an indicator for the laser pulse duration in the few cycle regime.     

Self-referencing, spectrally, or spatially encoded spectral interferometry for the complete characterization of attosecond electromagnetic pulses

We propose a method for the complete characterization of attosecond duration electromagnetic pulses produced by high harmonic generation in an atomic gas. Our method is based on self-referencing spectral interferometry of two spectrally sheared extreme ultraviolet pulses, which is achieved by pumping the harmonic source with two sheared optical driving pulses. The resulting interferogram contains sufficient information to completely reconstruct the temporal behavior of the electric field. We demonstrate that such a method is feasible, and outline two possible experimental configurations.     

Reshaping of attosecond x-ray pulses in thin crystals

A method for reshaping and control of the duration of attosecond x-ray pulses in thin crystals is proposed. The finite width of the reflection and transmission curves around the Bragg angle allows one to engineer Fabry-Perot-type filters for the generation of a large variety of attosecond pulse shapes. The method considered here can be used to manipulate attosecond pulses produced by high-harmonic generation and also for shorter wavelengths for attosecond pulses from x-ray free-electron lasers. X-ray pulses with controllable amplitude and phase may find useful applications in the newly emerging area of attosecond time-resolved spectroscopy.     

重复频率电磁脉冲对氢闸流管栅极的触发干扰

针对重复频率电磁脉冲（EMP）干扰,以氢闸流管的栅极触发电路为研究对象,进行了氢闸流管悬置与共地两种不同的条件下氢闸流管第一栅极与第二栅极的电磁干扰研究。结果表明,两种条件下两个栅极均存在较强烈的电磁干扰,干扰主要来源于空间电磁辐射与共地耦合两个方面;针对重复频率EMP环境下氢闸流管触发的可靠性,分别进行了不同重复频率EMP数量与不同重复频率EMP时间间隔下氢闸流管的输出实验。结果表明,两种情况均对氢闸流管的触发产生影响,重复频率EMP数量增多与间隔减小均使氢闸流管误触发的可能性增大,对比理论分析与实验结果,认为该现象是由于重复频率EMP累积效应与重复频率EMP高频分量增强从而导致交互作用耦合增强所引起。     

重复频率电磁脉冲对氢闸流管栅极的触发干扰

针对重复频率电磁脉冲（EMP）干扰,以氢闸流管的栅极触发电路为研究对象,进行了氢闸流管悬置与共地两种不同的条件下氢闸流管第一栅极与第二栅极的电磁干扰研究。结果表明,两种条件下两个栅极均存在较强烈的电磁干扰,干扰主要来源于空间电磁辐射与共地耦合两个方面;针对重复频率EMP环境下氢闸流管触发的可靠性,分别进行了不同重复频率EMP数量与不同重复频率EMP时间间隔下氢闸流管的输出实验。结果表明,两种情况均对氢闸流管的触发产生影响,重复频率EMP数量增多与间隔减小均使氢闸流管误触发的可能性增大,对比理论分析与实验结果,认为该现象是由于重复频率EMP累积效应与重复频率EMP高频分量增强从而导致交互作用耦合增强所引起。     

任意夹角的双色偏振激光作用下孤立阿秒脉冲的产生

本文选取脉宽为12 fs波长为2000 nm和800 nm的两束线性偏振激光, 适当调节两束激光的偏振方向的夹角θ, 发现当θ=π/2时, 高次谐波谱的第二级平台出现了“漏斗形”凹槽.当θ为π/6时, 得到了290 eV的超宽连续谱的高次谐波发射, 利用小波变换合理的解释了高次谐波形状及截止位置. 在该段连续谱上任意截取70 eV宽度的频率, 都可以得到脉宽约为60 as的孤立阿秒脉冲. 适当减小截取范围可以得到线性偏振的脉宽94 as的孤立阿秒脉冲. 这为实验中产生能灵活调节的孤立阿秒脉冲提供了一种方案.     

CMOS反相器的电磁干扰频率效应

利用自主开发的2维半导体器件-电路联合仿真器,研究了CMOS反相器在1 MHz～20 GHz电磁干扰作用下的响应。仿真结果表明：低频电磁干扰通过控制CMOS反相器中MOS管的导通、截止影响CMOS反相器的正常工作;高频电磁干扰通过MOS管中的本征电容耦合到输出端,干扰CMOS反相器的工作状态;CMOS反相器对于电磁干扰的敏感度随着干扰频率上升而不断降低。     

CMOS反相器的电磁干扰频率效应

利用自主开发的2维半导体器件-电路联合仿真器,研究了CMOS反相器在1 MHz～20 GHz电磁干扰作用下的响应。仿真结果表明:低频电磁干扰通过控制CMOS反相器中MOS管的导通、截止影响CMOS反相器的正常工作;高频电磁干扰通过MOS管中的本征电容耦合到输出端,干扰CMOS反相器的工作状态;CMOS反相器对于电磁干扰的敏感度随着干扰频率上升而不断降低。     

Frequency-resolved optical gating of isolated attosecond pulses in the extreme ultraviolet

The pulse shape and phase of isolated attosecond extreme ultraviolet (XUV) pulses with a duration of 860 asec have been determined simultaneously by using frequency-resolved optical gating based on two-photon above-threshold ionization with 28-eV photons in He. From the detailed characterization, we succeeded in shaping isolated XUV pulses on an attosecond time scale by precise dispersion control with Ar gas density or by changing the driving pulse width. These results offer a novel way to excite and observe an electron motion in atoms and molecules.     

利用两束同色圆偏振激光场产生水窗区间阿秒脉冲

数值研究了氦原子在两束同色圆偏激光场下发射高次谐波以及阿秒脉冲的特点.计算结果表明,当适当调节两束激光场的波长,相位以及时间延迟时,不仅高次谐波谱的平台区域能得到很大的扩展,而且谐波的强度也有较大的增强,形成了一个500 e V的超长平台区.最后,通过适当的叠加谐波平台上的谐波,可获得一系列脉宽为35 as左右的水窗区间阿秒脉冲.