Laser-sustained plasmas (LSP) enable high-resolution optical detection in chip fabrication, yet their spatiotemporal oscillations remain mysterious and strongly impede the development of high-brightness ultrabroadband stabilized light sources. We elucidate the fundamental origin and scaling of periodic oscillations in LSP through experiments and simulations. High-speed shadow imaging and validated multiphysics modeling reveal that the LSP oscillations stem from buoyancy-driven vortex dynamics, where periodic toroidal vortex ring formation and detachment—induced by the core-to-boundary density gradient—directly modulate plasma brightness. Crucially, we find that the Prandtl number (Pr) determines the LSP oscillation threshold (Pr > 0.6), while the Péclet number governs the oscillation patterns and frequency. A generalized scaling law incorporating the LSP core-to-boundary gas density ratio that enhances predictive accuracy is established. Further, we disentangle distinct thermal property roles, that is, a larger specific heat capacity promotes oscillations, whereas an increasing thermal conductivity suppresses instability. This study provides a mechanistic framework for LSP stability, enabling targeted suppression strategies to advance LSP-based light sources for high-resolution optical detection and spectroscopy in the field of the semiconductor industry.

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• Laser-plasma interactions
• Rayleigh-Taylor instability
• Vortex dynamics
• Optical plasma measurements