Vacuum-UV absorption spectrum of a laser-produced chromium plasma: 3p-subshell photoabsorption by Cr²⁺ions

Abstract

The dual laser plasma photoabsorption technique has been used to measure the time-resolved vacuum-UV photoabsorption spectrum of a chromium plasma. Resonant photoabsorption cross sections, constructed with the aid of Hartree-Fock calculations, and weighted in accordance with the plasma temperature, have been used to produce the synthetic Cr2+ spectra. The relevant plasma temperature and ionization balance are obtained from simple analytical models for various times during the expansion phase of the plasma plume. The experimental spectra taken at delays of 32, 62 and 90 ns compare well with Cr2+ spectra computed for corresponding predicted temperatures. It is found that in order to produce synthetic spectra that match experiment well, it is necessary to take into account absorption from many states belonging to the Cr2+ ground state configuration 3p63d4, while states from the nearest metastable configuration 3p63p34s make a negligible contribution.

3pphotoabsorption spectra ofMn2+andMn3Kilbane1, Mayo2, Kampen3 et al. 2007Phys. Rev. A1010View full textAdd to dashboardCite

“…The theoretical data have been shifted by +0.75 eV to fit the 3p − 4s resonances of the experimental spectrum. Comparing these data with observation, it is seen that the relative contributions expected for a plasma electron temperature (T e ) of 2.5 eV fit the experimental data quite well and compare favourably with the temperature quoted for Cr 2+ (T e = 3.3 eV) [3]. This accounts for the presence of metastables in the plasma which contribute to the photoabsorption spectrum of Mn 2+ recorded here.…”

“…The 3p→ns (n ≥ 5) and the 3p→4d transitions occur at higher energies than experimentally recorded here. As was observed in [3] for Cr 2+ (which is isoelectronic with Mn 3+ ), photoabsorption from states of the 3d 3 4s configuration does not play a significant role in determining the overall shape and structure of the experimental photoabsorption spectrum and they are therefore omitted from this figure. Fig.…”

“…We account for these metastable contributions by superimposing calculated cross sections for several individual low-lying terms weighted according to a Boltzmann distribution for several plasma temperatures [2,3]. A multitude of low lying states are positioned above the 3d 5 , which lies at 7.744 eV [22].…”

“…EUV photoabsorption and photoion spectra of ions of chromium (Costello et al [1], McGuinness et al [2,3], West et al [4]), manganese (Cooper et al [5], Costello et al [1], Kjeldsen et al [6]) and iron (Kjeldsen [7]) and theoretical studies by Dolmatov [8][9][10][11][12] and Donnelly [13][14][15][16] gave rise to significant debate. A recent photoabsorption experiment by Kilbane et al [17] confirmed Dolmatov's predictions [9], that between Mn + and Mn 2+ , not only do the 3p-4s resonances swap over to the high energy side of the giant 3p-3d resonance but also that this reordering has significant effects on the resonance profiles.…”

10.1007/s11449-008-2019-4

“…Our investigations using 35-fs pulses showed that the 29th harmonic (λ = 27.6 nm, E ph ≈ 45.1 eV) is enhanced at the leading edge of the strong spectral band of the 3p 3d transitions of chromium ions. At the same time, previous investigations of the photoabsorption and photoionization spectra of chromium plasma in the region from 41 to 42 eV showed the existence of transitions with high oscillator strengths, which can be responsible for the strong absorption (in particular, of the 27th harmonic) [43][44][45]. These and other studies of the photoabsorption spectra of chromium allowed one to identify the ranges of strong absorption in the FUV region.…”