Topological modes in a laser cavity through exceptional state transfer

Shaping the light emission characteristics of laser systems is of great importance in various areas of science and technology. In a typical lasing arrangement, the transverse spatial profile of a laser mode tends to remain self-similar throughout the entire cavity. Going beyond this paradigm, we demonstrate here how to shape a spatially evolving mode such that it faithfully settles into a pair of bi-orthogonal states at the two opposing facets of a laser cavity. This was achieved by purposely designing a structure that allows the lasing mode to encircle a non-Hermitian exceptional point while deliberately avoiding non-adiabatic jumps. The resulting state transfer reflects the unique topology of the associated Riemann surfaces associated with this singularity. Our approach provides a route to developing versatile mode-selective active devices and sheds light on the interesting topological features of exceptional points. Description An exceptional laser cavity Laser cavities are typically simple structures in the sense that the pump light oscillates between the cavity walls symmetrically, ideally with a single resonant output mode. More complex cavity designs exploiting materials exhibiting gain and loss can be realized that result in an exceptional point at which the output mode can effectively be tuned. Schumer et al. designed a cavity in which the pump light encircles the exceptional point as it propagates back and forth within the cavity. The result is a laser capable of simultaneously emitting in two different, but topologically linked, transverse profiles, each from a different facet of the cavity. The approach provides flexibility in designing topologically robust laser cavities. —ISO A laser cavity is designed with a spatial mode that exploits the topology surrounding an exceptional point.