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Formation Dynamics of Excited Neutral Nitrogen Molecules inside Femtosecond Laser Filaments
摘要： Nitrogen molecules are promoted to excited neutral states during femtosecond laser pulse filamentary propagation in atmosphere, leading to a characteristic UV fluorescence. Using a laser-induced fluorescence depletion technique, we measure the formation dynamics of these excited neutral nitrogen molecules with femtosecond time resolution. We find that the excited neutral molecules are formed in an unexpected ultrafast timescale of ～4 ps at 1 bar and ～120 ps at 30 mbar pressure. From this observation we deduce that the excitation of neutral N2 occurs via multiple collisions with hot free electrons. Numerical simulations based on rate equations reproduce well this ultrafast formation time and its dependence on gas pressure, and thus support this interpretation.
关键词： electron impact excitation,femtosecond laser,plasma filament,UV fluorescence,nitrogen molecules
更新于2025-09-12 10:27:22
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Polarization of fluorescence radiation following electron impact excitation of ions immersed in strongly coupled plasmas
摘要： An investigation on the electron impact excitation and subsequent radiative decay process of He-like Fe24t ions immersed in strongly coupled plasmas is made, using the 1s2p 3;1P1 ! 1s2 1S0 characteristic lines as an example. The shielded nuclear potential of the uniform electron gas model (UEGM) type experienced by the electron is parameterized by the ion-sphere radius. For the target structure, accuracies of wave functions are justified by evaluating the energies of the relevant states. To serve as an independent check of the results, self-consistent calculations are carried out using the multiconfiguration Dirac-Fock relativistic configuration interaction method incorporating the same potential. For the impact excitation process, the UEGM potential is also employed to screen the projectile electron from the nucleus and target electrons. A distorted-wave method in the framework of the relativistic theory is developed to include the effect of plasma background, in which the continuum wave function of the projectile electron is evaluated by solving numerically the modified Dirac equations. The plasma effects on the total excitation cross section, magnetic sublevel cross section, and linear polarization of fluorescence radiation are investigated. The comparison with the available theoretical and experimental results is satisfactory.
关键词： UEGM potential,linear polarization,He-like Fe24t ions,electron impact excitation,strongly coupled plasmas,radiative decay
更新于2025-09-12 10:27:22
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Spectroscopic diagnostics of low-ionized iron-peak elements. Electron-impact excitation of Ni3 + and photoionization of Ni2 +.
摘要： The spectra from Fe-peak elements may be used to determine the temperature and density of various astrophysical objects. Determination of these quantities is underpinned by the accuracy and the comprehensiveness of the underlying atomic structure and collisional calculations. In the following paper, we shall focus specifically on Ni iv lines associated with transitions amongst several low-lying levels. We shall employ modified versions of the parallel Dirac R-matrix codes, considering both electron-impact excitation of Ni3+ and the photoionisation of both the ground and excited states of Ni2+. We produce high-quality data sets for both processes, and using these data, we calculate line ratios relevant for plasma diagnostics of temperature and density.
关键词： opacity,Atomic data,electron-impact excitation,photoionization
更新于2025-09-04 15:30:14
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Collisional - radiative model of xenon plasma with calculated electron impact fine-structure excitation cross sections
摘要： Detailed electron impact excitation cross section results for xenon in the wide range of incident energy from threshold to 1000eV are calculated using relativistic distorted wave (RDW) theory. Various transitions from the ground 5p6 state to the excited 5p56s, 5p56p, 5p55d, 5p57s and 5p57p as well as among these excited states are considered. The relativistic Dirac-Fock multi-configuration wave functions for the ground and excited states of the xenon are obtained and used in the calculations. Where available our cross section results are compared with previously reported measurements and calculations. We have also fitted the calculated cross sections through analytical formulae for plasma modeling purposes. As an application, using the obtained cross sections, a collisional Radiative (C-R) model coupled with an optical emission measurement from the inductively coupled Xe plasma is developed and the extracted plasma parameters are reported.
关键词： relativistic distorted wave theory,Electron impact excitation,cross-sections,collisional radiative model
更新于2025-09-04 15:30:14