Mainz 2017 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 19: Clusters II (with A)

MO 19.2: Vortrag

Freitag, 10. März 2017, 11:30–11:45, N 3

NIR-induced Auger decay in clusters — •Bernd Schütte, Marc Vrakking, and Arnaud Rouzée — Max-Born-Institut, Berlin

In nanoplasmas, which are formed by the interaction of clusters with intense laser pulses, Rydberg states are efficiently populated. While it is well known that some of the excited atoms and ions relax via the emission of photons [1], nonradiative relaxation mechanisms have only recently been discovered at moderate cluster ionization [2,3]. Here we show that nonradiative decay remains important at high ionization degrees, as is demonstrated for CH₄ clusters that interact with 400-fs NIR pulses (I=1× 10¹⁴ W/cm²). We observe a clear peak in the electron spectrum at 7 eV that is assigned to Auger decay, and that is explained by a 3-step process: (i) Our calculations show that the laser pulse removes almost all electrons from the outer shells of C, resulting in a dominant C⁴⁺ ion contribution at the end of the laser pulse. (ii) Rydberg and outer-vacancy shell levels are populated by recombination, and (iii) relax via Auger decay. This picture is consistent with a dominant C³⁺ ion contribution observed in the experiment, whereas, surprisingly, C⁺ and C⁴⁺ ion contributions are negligible.

Our results could explain the high average ion charge states that have been observed in clusters in spite of highly efficient recombination processes. Furthermore, the observed population inversion may be exploited for the development of an XUV or X-ray laser.

[1] A. McPherson et al., Nature 370, 631 (1994).

[2] B. Schütte et al., Phys. Rev. Lett. 114, 123002 (2015).

[3] B. Schütte et al., Nat. Commun. 6, 8596 (2015).