Comparison of nanoplasma ignition in helium nanodroplets induced by molecular and atomic dopants

We experimentally compare nanoplasma ignition in a helium (He) nanodroplet doped with either oxygen molecules (O2) or xenon atoms (Xe) under intense near-infrared femtosecond laser pulses. At low dopant concentrations, Xe demonstrates higher ignition efficiency than O2. However, as dopant concentration increases, O₂ surpasses Xe due to the weaker intermolecular interactions of O₂ with He atoms, which reduce He evaporation losses. The yields and relative abundances of He_n · He+ ions (n = 0, 1, 2) exhibit distinct trends for O₂ and Xe, reflecting a competition between dopant-assisted ionization and neutral He depletion. At higher laser intensities, O2 exhibits reduced efficiency compared to Xe, underscoring the critical influence of molecular electronic structures on nanoplasma-ignition dynamics. We also examine the role of droplet size in these processes. Our results reveal the potential of molecular dopants like O₂ to enable tailored ignition strategies for nanoplasma applications.