Abstract
The multiple ionisation of atomic Mn, excited at (photon energy: 52.1 eV) and above (photon energy: 61.1 eV) the discrete giant resonance, was studied using high irradiation free-electron-laser soft x-ray pulses from the BL2 beamline of FLASH, DESY, Hamburg. In particular, the impact of the giant resonance on the ionisation mechanism was investigated. Ion mass-over-charge spectra were obtained by means of ion time-of-flight spectrometry. For the two photon energies, the yield of the different ionic charge states Mn (q = 0–7) was determined as a function of the irradiance of the soft x-ray pulses. The maximum charge state observed was Mn6+ for resonant excitation at 52.1 eV and Mn7+ for non-resonant excitation at 61.1 eV at a maximum irradiation of .
Highlights
Since the discovery of the photoelectric effect by Hertz [1] and its explanation by Einstein [2] it has been used extensively to study the interaction between light and matter
The vapour was crossed with the pulsed focused photon beam from FLASH in the interaction region of the mass-spectrometer
The beamline delivers photon pulses with a typical energy bandwidth of one percent of the photon energy [20, 86] and a pulse duration in the order of t = (100 10) fs (FWHM). The latter was estimated by measuring a single-shot spectral intensity profile at the PG2 beamline of FLASH before and after the experiment as well as by online determination of the length of the electron bunch [87]
Summary
Since the discovery of the photoelectric effect by Hertz [1] and its explanation by Einstein [2] it has been used extensively to study the interaction between light and matter. With the upcoming lasers in the 1960s, the ionisation of atoms with optical light via multi-photon absorption became possible [3] using an optical ruby laser with a wavelength of 694.3 nm (photon energy: 1.78 eV). The nonlinear multi-photon photoionisation was afterwards an active field in the 1970s and 1980s [4,5,6,7,8], but limited to the optical regime because only optical lasers were able to generate sufficiently high electromagnetic fields [9, 10]. [7, 16]) while the first light source generating pulses in the soft x-ray regime with sufficient photon densities [17] for multi-photon excitation was the free electron laser (FEL) FLASH (formerly TTF [18]) built by DESY [19,20,21]. At the VUV-FEL facility SCSS in Japan, the multi-photon multiple ionisation of argon was reported at 20 eV and 2 ́ 1014 W cm-2 [27]
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