This work challenges the conventional rule that the highest‑Q mode always reaches the lasing threshold first under uniform gain. By studying non‑Hermitian degeneracies (exceptional points) in laser cavities, the authors show that lower‑quality‑factor modes can coalesce and accelerate toward threshold, surpassing initially more favorable modes. JCMsuite’s finite‑element solver was used to compute the quasi‑normal modes of a designed polygonal microcavity and to trace their complex‑frequency trajectories as gain is increased, thereby validating the predicted exceptional‑point‑induced mode switching.
J. Kullig, et al. Exceptional Points and Lasing Thresholds: When Lower-Q Modes Win. Phys. Rev. Lett. 135, 173802 (2025).
DOI: 10.1103/zc6x-pfw2