Driven-dissipative optical microcavities provide a versatile platform for exploring lasing dynamics far from equilibrium. While the Kibble-Zurek mechanism provides a framework for understanding non-equilibrium phase transitions, the critical dynamics associated with first-order phase transitions in microlasers, particularly as a non-Hermitian system, remains largely unexplored. Here we report the temporal critical behavior of lasing-state transitions in an ultrahigh-Q whispering-gallery microlaser. By dynamically ramping a non-Hermitian interferometric coupling, the laser switches between two nearly degenerate standing-wave supermodes with opposite parities. Using radio-frequency beat-note readout with high resolution, we directly capture the real-time switching process and measure the transition time as a function of the ramp speed. A power-law scaling is found with an exponent of $\sim 0.5$, which also remains robust in coupled-cavity laser networks, setting a fundamental speed limit for microcavity laser state conversion.

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• Laser dynamics
• Optical microcavities
• Microcavity & microdisk lasers