A generalized kinetic model of atomic level populations in an optically dense plasma excited by laser pulses of arbitrary duration is formulated and studied.This model is based on a nonstationary expression for the pr...A generalized kinetic model of atomic level populations in an optically dense plasma excited by laser pulses of arbitrary duration is formulated and studied.This model is based on a nonstationary expression for the probability of excitation of an atomic transition and takes into account the effects of laser pulse penetration into an optically dense medium.A universal formula for the excitation probability as a function of time and propagation length is derived and applied to the case of a Lorentzian spectral profile of an atomic transition excited by a laser pulse with a Gaussian envelope.The features of nonstationary excitation probabilities are presented for different optical depths of the plasma,laser pulse durations,and carrier frequencies.The formulas derived here will be useful for the description of atomic populations excited by laser pulses under realistic conditions of dense plasmas.展开更多
Statistical models combined with the local plasma frequency approach applied to the atomic electron density are employed to study the photoionization cross-section for complex atoms.It is demonstrated that the Thomas...Statistical models combined with the local plasma frequency approach applied to the atomic electron density are employed to study the photoionization cross-section for complex atoms.It is demonstrated that the Thomas–Fermi atom provides surprisingly good overall agreement even for complex outer-shell configurations,where quantum mechanical approaches that include electron correlations are exceedingly difficult.Quantum mechanical photoionization calculations are studied with respect to energy and nl quantum number for hydrogen-like and non-hydrogen-like atoms and ions.Ageneralized scaled photoionizationmodel(GSPM)based on the simultaneous introduction of effective charges for non-H-like energies and scaling charges for the reduced energy scale allows the development of analytical formulas for all states nl.Explicit expressions for nl1s,2s,2p,3s,3p,3d,4s,4p,4d,4f,and 5s are obtained.Application to H-like and non-H-like atoms and ions and to neutral atoms demonstrates the universality of the scaled analytical approach including inner-shell photoionization.Likewise,GSPMdescribes the near-threshold behavior and high-energy asymptotes well.Finally,we discuss the various models and the correspondence principle along with experimental data and with respect to a good compromise between generality and precision.The results are also relevant to large-scale integrated light–matter interaction simulations,e.g.,X-ray free-electron laser interactions with matter or photoionization driven by a broadband radiation field such as Planckian radiation.展开更多
The theory of photoionization describing the interaction of x-ray free-electron laser(XFEL)pulses and high-harmonic-generated(HHG)radiation is generalized to ultrashort laser pulses,where the concept of the standard i...The theory of photoionization describing the interaction of x-ray free-electron laser(XFEL)pulses and high-harmonic-generated(HHG)radiation is generalized to ultrashort laser pulses,where the concept of the standard ionization probability per unit time in Fermi’s golden rule and in Einstein’s theory breaks down.Numerical calculations carried out in terms of a generalized photoionization probability for the total duration of pulses in the near-threshold regime demonstrate essentially nonlinear behavior,while absolute values may change by orders of magnitude for typical XFEL and HHG pulses.XFEL self-amplified spontaneous emission pulses are analyzed to reveal general features of photoionization for random and regular spikes:the dependences of the nonlinear photoionization probability on carrier frequency and spike duration are very similar,allowing an analytical expectation value approach that is valid even when there is only limited knowledge of random and regular parameters.Numerical simulations carried out for typical parameters demonstrate excellent agreement.展开更多
On the basis of equations obtained in the framework of second-order quantum-mechanical perturbation theory,the standard approach to the calculation of scattering radiation probability is extended to the case of ultras...On the basis of equations obtained in the framework of second-order quantum-mechanical perturbation theory,the standard approach to the calculation of scattering radiation probability is extended to the case of ultrashort laser pulses.Weinvestigate the mechanism of the appearance of plasmon peaks in the spectrum of the plasma form factor for different parameters of the problem.For the case in which scattering on plasmons dominates over scattering on electron density fluctuations caused by chaotic thermal motion,we derive analytical expressions describing the scattering probability of ultrashort laser pulses on plasmons.Together with this,we obtain a simple expression connecting the frequency of scattered radiation and the energy transmitted from the incident pulse to plasmon,and vice versa.In considering the scattering probability,our emphasis is on the dependence on the pulse duration.Weassess in detail the trends of this dependence for various relations between pulse carrier frequency and plasmon energy.展开更多
Novel phenomena andmethods related to dielectronic capture and dielectronic recombination are studied for non-local thermodynamic equilibrium(LTE)plasmas and for applications to non-LTE ionization balance.It is demons...Novel phenomena andmethods related to dielectronic capture and dielectronic recombination are studied for non-local thermodynamic equilibrium(LTE)plasmas and for applications to non-LTE ionization balance.It is demonstrated thatmultichannel autoionization and radiative decay strongly suppress higher-order contributions to the total dielectronic recombination rates,which are overestimated by standard approaches by orders of magnitude.Excited-state coupling of dielectronic capture is shown to be much more important than ground-state contributions,and electron collisional excitation is also identified as a mechanism driving effective dielectronic recombination.A theoretical description of the effect of angularmomentum-changing collisions on dielectronic recombination is developed from an atomic kinetic point of view and is visualized with a simple analytical model.The perturbation of the autoionizing states due to electric fields is discussed with respect to ionization potential depression and perturbation of symmetry properties of autoionizationmatrix elements.The first steps in the development of statistical methods are presented and are realized in the framework of a local plasma frequency approach.Finally,the impact of collisional–radiative processes and atomic population kinetics on dielectronic recombination is critically discussed,and simple analytical formulas are presented.展开更多
基金supported by the Ministry of Science and Higher Education of the Russian Federation(Goszadaniye)No.075-03-2024-107.
文摘A generalized kinetic model of atomic level populations in an optically dense plasma excited by laser pulses of arbitrary duration is formulated and studied.This model is based on a nonstationary expression for the probability of excitation of an atomic transition and takes into account the effects of laser pulse penetration into an optically dense medium.A universal formula for the excitation probability as a function of time and propagation length is derived and applied to the case of a Lorentzian spectral profile of an atomic transition excited by a laser pulse with a Gaussian envelope.The features of nonstationary excitation probabilities are presented for different optical depths of the plasma,laser pulse durations,and carrier frequencies.The formulas derived here will be useful for the description of atomic populations excited by laser pulses under realistic conditions of dense plasmas.
基金The work described here was supported by the Cooperation Agreement between the Sorbonne University,Faculty of Sciences(Pierre and Marie Curie)and the Moscow Institute of Physics and Technology MIPTFinancial support from MIPT in the framework of Grant No.075-02-2019-967 and the 5-top-100 program is greatly acknowledgedThis work has also been supported by the Competitiveness Program of NRNU MEPhI in the framework of the Russian Academic Excellence Project.
文摘Statistical models combined with the local plasma frequency approach applied to the atomic electron density are employed to study the photoionization cross-section for complex atoms.It is demonstrated that the Thomas–Fermi atom provides surprisingly good overall agreement even for complex outer-shell configurations,where quantum mechanical approaches that include electron correlations are exceedingly difficult.Quantum mechanical photoionization calculations are studied with respect to energy and nl quantum number for hydrogen-like and non-hydrogen-like atoms and ions.Ageneralized scaled photoionizationmodel(GSPM)based on the simultaneous introduction of effective charges for non-H-like energies and scaling charges for the reduced energy scale allows the development of analytical formulas for all states nl.Explicit expressions for nl1s,2s,2p,3s,3p,3d,4s,4p,4d,4f,and 5s are obtained.Application to H-like and non-H-like atoms and ions and to neutral atoms demonstrates the universality of the scaled analytical approach including inner-shell photoionization.Likewise,GSPMdescribes the near-threshold behavior and high-energy asymptotes well.Finally,we discuss the various models and the correspondence principle along with experimental data and with respect to a good compromise between generality and precision.The results are also relevant to large-scale integrated light–matter interaction simulations,e.g.,X-ray free-electron laser interactions with matter or photoionization driven by a broadband radiation field such as Planckian radiation.
基金funded by RFBR Grant No.19-32-90016,Ecole Polytechnique,the Cooperation Agreement between the Sorbonne University and MIPT,and the MIPT 5-top-100 programsupported by the Competitiveness Program of NRNU MEPhI in the framework of the Russian Academic Excellence Project.
文摘The theory of photoionization describing the interaction of x-ray free-electron laser(XFEL)pulses and high-harmonic-generated(HHG)radiation is generalized to ultrashort laser pulses,where the concept of the standard ionization probability per unit time in Fermi’s golden rule and in Einstein’s theory breaks down.Numerical calculations carried out in terms of a generalized photoionization probability for the total duration of pulses in the near-threshold regime demonstrate essentially nonlinear behavior,while absolute values may change by orders of magnitude for typical XFEL and HHG pulses.XFEL self-amplified spontaneous emission pulses are analyzed to reveal general features of photoionization for random and regular spikes:the dependences of the nonlinear photoionization probability on carrier frequency and spike duration are very similar,allowing an analytical expectation value approach that is valid even when there is only limited knowledge of random and regular parameters.Numerical simulations carried out for typical parameters demonstrate excellent agreement.
基金funded by MIPT in the framework of the 5-Top-100 Programsupported by RFBR,Project No.19-32-90016.
文摘On the basis of equations obtained in the framework of second-order quantum-mechanical perturbation theory,the standard approach to the calculation of scattering radiation probability is extended to the case of ultrashort laser pulses.Weinvestigate the mechanism of the appearance of plasmon peaks in the spectrum of the plasma form factor for different parameters of the problem.For the case in which scattering on plasmons dominates over scattering on electron density fluctuations caused by chaotic thermal motion,we derive analytical expressions describing the scattering probability of ultrashort laser pulses on plasmons.Together with this,we obtain a simple expression connecting the frequency of scattered radiation and the energy transmitted from the incident pulse to plasmon,and vice versa.In considering the scattering probability,our emphasis is on the dependence on the pulse duration.Weassess in detail the trends of this dependence for various relations between pulse carrier frequency and plasmon energy.
基金This work was supported by the Cooperation Agreement between the Sorbonne University(Faculty of Sciences)the Moscow Institute of Physics and Technology-MIPT.Financial support from MIPT under Grant No.075-02-2019-967 in the framework of the 5-top-100 program is greatly acknowledged.
文摘Novel phenomena andmethods related to dielectronic capture and dielectronic recombination are studied for non-local thermodynamic equilibrium(LTE)plasmas and for applications to non-LTE ionization balance.It is demonstrated thatmultichannel autoionization and radiative decay strongly suppress higher-order contributions to the total dielectronic recombination rates,which are overestimated by standard approaches by orders of magnitude.Excited-state coupling of dielectronic capture is shown to be much more important than ground-state contributions,and electron collisional excitation is also identified as a mechanism driving effective dielectronic recombination.A theoretical description of the effect of angularmomentum-changing collisions on dielectronic recombination is developed from an atomic kinetic point of view and is visualized with a simple analytical model.The perturbation of the autoionizing states due to electric fields is discussed with respect to ionization potential depression and perturbation of symmetry properties of autoionizationmatrix elements.The first steps in the development of statistical methods are presented and are realized in the framework of a local plasma frequency approach.Finally,the impact of collisional–radiative processes and atomic population kinetics on dielectronic recombination is critically discussed,and simple analytical formulas are presented.
