Time-resolved studies on the collapse of magnesium atom foam in helium nanodroplets

Magnesium atoms embedded in superfluid helium nanodroplets have been identified to arrange themselves in a metastable network, referred to as foam. In order to investigate the ionization dynamics of this unique structure with respect to a possible light-induced collapse, the femtosecond dual-pulse spectroscopy technique is applied. Around zero optical delay a strong feature is obtained which represents a direct probe of the foam response. We found that upon collapse, ionization is reduced. A particular intensity ratio of the pulses allows us to address either direct ionization or photoactivation of the neutral complexes, thus affecting reaction pathways. A simplified scheme visualizes possible excitation scenarios in accordance with the experimental observations.