Observation of Centrally Converging Airflow Columns Induced by Heat Accumulation in High-Repetition-Rate Femtosecond Laser Filaments

This study first reveals a thermally driven airflow phenomenon in high-repetition-rate (1~100 kHz) femtosecond laser filaments, characterized by the formation of a stable, perpendicularly oriented central converging airflow column. Using transverse optical shadowgraphy, we directly visualize the filament-induced flow dynamics and find that the airflow intensity and spatial coherence increase almost linearly with repetition rates above 10 kHz. Thermofluidic simulations indicate that cumulative heat deposition from successive pulses governs the evolution of airflow column, transforming initially diffuse vortices into a symmetric dual-vortex structure. And the particle-tracing simulations confirm that acoustic heating contributes negligibly to the overall flow dynamics. These findings further confirm that heat accumulation plays a predominant role in governing filament–air interactions and reveal a distinct thermally induced converging airflow phenomenon, offering new insight into the thermal dynamics of high-repetition-rate filamentation.