Tabletop XUV Spectroscopy of Uranium Oxides From Laser-Produced Plasmas Using Ultrafast Laser-Driven High Harmonic Generation

Uranium oxide conglomerates, formed during pulsed laser ablation of uranium metal targets in oxygen-containing environments, have recently been used to simulate debris from nuclear detonations in forensics. However, current literature lacks mature understanding of the complex gas-phase reaction kinetics which result in the formation of uranium oxide conglomerates nor their precise final structure and composition. Often, existing nondestructive optical spectroscopic methods (vibrational, UV/visible absorption or emission) do not offer clear signatures that can be used to distinguish the various oxide species within these conglomerates because of overlapping features populated by dense electronic transitions. In addition, measuring distinct spectroscopic signatures of subtly different f-electron compounds, those differing only by oxidation state, or organo-metallic complexes with different ligands, is important for understanding more general f-electron chemistry. In present work, we aim to study these conglomerates originating from uranium-containing laser-produced plasmas using eXtreme UltraViolet (XUV) spectroscopy enabled by ultrafast laser-driven high harmonic generation (HHG). HHG provides a tabletop alternative for photon energies that reach actinide O- and N-edges (−30-150 eV) otherwise only available at user-facilities like synchrotrons or free electron lasers, where accessibility and limited ability to handle radiological samples pose challenges toward measurements on actinides.