Spatial and Spectral Mode-Selection Effects in Topological Lasers with Frequency-Dependent Gain

Matteo Seclì


When different modes of a laser cavity have different spatial profiles, a common strategy in order to lase in a specific mode is to increase its spatial overlap with the gain material; this mechanism has been used in several recent topolaser realizations, e.g. in the one by M. Bandres and co-authors, whereby the topological edge mode was selected by concentrating the pump along the edge. Here, we go beyond this simple spatial mode-selection scheme by including the additional spectral mode-selection mechanism coming from the frequency-dependence of gain. In particular, we take motivation from the recent topolaser experiment by B. Bahari and co-authors to investigate how a subtle combination of spectral and spatial mode-selection mechanisms can conspire to stabilize laser oscillation into a chiral edge state, and we point out a possible mechanism for their still unexplained experimental observation of single-mode emission under a spatially homogeneous pump.

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