Non-Hermitian physical systems have attracted considerable attention lately for their unconventional behaviour around exceptional points (EPs)—spectral singularities at which eigenvalues and eigenvectors coalesce. In particular, many new EP-related concepts such as unidirectional lasing and invisibility, as well as chiral transmission, have been realized. Given the progress in understanding the physics of EPs in various photonic structures, it is surprising that one of the oldest theoretical predictions associated with them, a remarkable broadening of the laser linewidth at an EP, has been probed only indirectly so far. Here, we fill this gap by steering a phonon laser through an EP in a compound optomechanical system formed by two coupled resonators. We observe a pronounced linewidth broadening of the mechanical lasing mode generated in one of the resonators when the system approaches the EP.

非Hermitian物理系统近来因其围绕例外点（EPs）的非常规行为而引起了相当大的关注，这些例外点是特征值和特征向量合并的谱奇点。特别地，已经实现了许多新的与EP相关的概念，例如单向激光和隐形以及手性传输。鉴于在理解各种光子结构中的EP物理学方面取得了进步，令人惊讶的是，到目前为止，仅间接地探讨了与它们相关的最古老的理论预测之一，即EP处激光线宽的显着扩大。在这里，我们通过在两个耦合谐振器形成的复合光机械系统中通过声子使声子激光穿过EP来填补这一空白。