We experimentally compare nanoplasma ignition in a helium (He) nanodroplet doped with either oxygen molecules $\left({\mathrm{O}}_2\right)$ or xenon atoms (Xe) under intense near-infrared femtosecond laser pulses. At low dopant concentrations, Xe demonstrates higher ignition efficiency than ${\mathrm{O}}_2$. However, as dopant concentration increases, ${\mathrm{O}}_2$ surpasses Xe due to the weaker intermolecular interactions of ${\mathrm{O}}_2$ with He atoms, which reduce He evaporation losses. The yields and relative abundances of ${\mathrm{He}}_n·\mathrm{H}{\mathrm{e}}^{+}$ ions $(n=0, 1, 2)$ exhibit distinct trends for ${\mathrm{O}}_2$ and Xe, reflecting a competition between dopant-assisted ionization and neutral He depletion. At higher laser intensities, ${\mathrm{O}}_2$ 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 ${\mathrm{O}}_2$ to enable tailored ignition strategies for nanoplasma applications.

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• Atomic & molecular processes in external fields
• Laser-cluster interaction
• Multiphoton or tunneling ionization & excitation
• Plasmonics