Ultrafast lasers for attosecond science - Nature

A central problem in semiconductor lasers is deceptively simple: how can one increase optical performance without allowing unwanted modes to oscillate? In broad-area semiconductor lasers, increasing the emission area increases the available power, but it also favors many-mode oscillation and degraded beam quality. Photonic-crystal surface-emitting lasers have addressed this problem by engineering optical coupling inside a two-dimensional photonic lattice. In the large-area limit, recent works have shown that single-mode operation can be preserved by controlling Hermitian and non-Hermitian couplings so that higher-order modes experience larger radiation losses than the fundamental mode1. The lesson is broader than the particular device: a good laser is not defined only by the quality factor (Q) of one mode, but by the threshold margin separating that mode from all its competitors. Recently published in Light: Science & Applications, the work of Peng and colleagues, “Robust single-mode laser via merging bound state in the continuum”, brings this principle into the realm of compact bound-state-in-the-continuum lasers2.