Two-photon double-resonant excitation of the Xe* autoionization states using synchronized laser and synchrotron radiation pulses

Abstract

The technique of synchronization between the pulses of a linear dye laser, synchronously pumped by a mode-locked Ar + laser, and the synchrotron radiation pulses from the SuperACO storage ring in Orsay (France) has been applied to study the photoionization of the Xe* 5p 5 5d [3/2] 1 and Xe* 5p 5 6d [3/2] 1 excited states in the energy region between the Xe + 5p 5 ( 2 P 3/2 ) and ( 2 P 1/2 ) thresholds. The experimental spectra are dominated by strong transitions to the Xe* 5p 5 nf [5/2] 2 autoionization resonances, which are characterized by typical asymmetric Fano-type line profiles. The energy positions of the n = 4, 7-13 resonances have been measured. For the 4f [5/2] 2 and nf [5/2] 2 (n = 7-9) resonances, the asymmetry parameter q and the linewidth could be determined upon photoexcitation from the intermediate state 5d [3/2] 1 and 6d [3/2] 1 , respectively. As a general behaviour of the investigated excitations, the oscillator strengths for d → f transitions were found to exceed by far those for the, also dipole-allowed, d → p transitions. Two-photon excitations are a specific, but very subtle and powerful tool to investigate the complex interactions in the electronic subshells of atoms or molecules. In a 'pumpprobe' arrangement the first photon is used to prepare a particular, well defined excited state which is subsequently analysed by the second photon. In this way it is possible to investigate various physical subjects, such as excited states which are not accessible by one-photon excitation due to dipole selection rules, processes related to photo-induced molecular dissociation, consequences of a change in the electronic configuration for the photoionization of a particular subshell, or effects related to aligned or oriented species. Beside the large number of experiments dealing with two (or more) lasers (see, for example, Klar et al 1992, Kung and Lee 1991 and references therein), the combination of synchrotron radiation (SR) and conventional lasers has opened new exciting research fields, related to the inner-shell photoionization of laser-excited atoms (e.g. Bizau et al 1985) and the study of free radicals produced by laser-induced dissociation (e.g. Nahon and Morin 1992). The specific characteristics of a CW laser (high photon flux, high spectral resolution and high degree of polarization) have been fully exploited in the 'pump' process for the production of a high density of excited atoms (e.g. Cubaynes et al 1989) or for the detailed study of the photoionization process by investigating aligned atomic states (e.g. Wedowski et al 1997).

Millimeter-wave spectroscopy and multichannel quantum-defect-theory analysis of high Rydberg states of xenon: The hyperfine structure ofXe129+andSchäfer1, Raunhardt2, Merkt3 2010Phys. Rev. A

“…values of Refs. [41,44] for the nf [5/2] 2 autoionizing Rydberg series have been adopted, instead of the values of Ref. [11]; and (3) the resonance positions given in Refs.…”

Synchrotron-laser two-color experiments: Two-photon double-resonant excitation of Ar to autoionization states between the 2P3/2 and 2P1/2 ionic thresholds

“…The observation of the forbidden transitions, nf' and np', between the core configurations indicates a strong configuration interaction. These series were reported by Meyer et al based on results from the SuperACO storage ring [5]. In the case of argon, by setting the energy of SR to 14.304 eV (corresponding to 115,366.8 cm -1 ), 3p 5 ( 2 P 1/2 )3d' [3/2] 1 autoionization resonances can be excited within the wavelength region of the tunable laser.…”

“…The intense series is identical to that reported in ref. [5] for the 3p5nf' [5/2] 2 series, except that line shapes of this series are nearly symmetric.…”

Combination of lasers and synchrotron radiation in studies of atomic photoionization

“…In order to separate the two-color ionization signal from the intense background arising from the second and third order light of the monochromator, the electrons were analyzed with respect to their kinetic energy allowing to distinguish ionization processes caused by the simultaneous action of the SR and laser pulses and those induced by higher photon energies of the SR. Improvements in beamline performances, especially the suppression of higher order light, has enabled later on the more efficient and simpler ion detection for this type of studies [40].…”