Femtosecond lasers have been applied in the machining of zirconia ( \({{\textrm{ZrO}}_2}\) ) ceramics because of their ultrashort pulse duration and high peak power. However, the high-precision micromachining of zirconia remains challenging owing to an unclear understanding of the ultrafast laser–material interaction mechanisms. In this study, the transient processing phenomenon induced by a femtosecond laser pulse, namely electron excitation (filament), occurring on a picosecond to nanosecond timescale, was directly observed and quantitatively investigated inside \({{\textrm{ZrO}}_2}\) . A pump-probe imaging method comprising a focusing probe beam integrated with a high-speed camera was used. The evolution process, type variation, and related interaction mechanisms of the filament were revealed under different parameters, including laser pulse energy, sample position, and pulse duration. Finally, the generation mechanism of multiple filaments was clarified and successfully elucidated. This study reveals the ultrafast laser–material interaction mechanisms and the high-precision processing in the laser drilling of zirconia ceramics.
