Abstract: A TiO2 split-square-slot metasurface for highly efficient lasing in the visible is proposed and studied. The slot is filled with highly fluorescent rhodamine 6G (R6G) molecules dissolved in methanol, providing optically pumped gain under pulsed excitation at 532 nm. Lasing is enabled via a slot-type quasi-bound state in the continuum (qBIC) resonance, while the pump light is effectively coupled to a bright mode of the metasurface maximizing the absorption efficiency. Highly performing lasing is achieved with very low threshold of ~ 1 kW/cm2 and remarkably high overall efficiency of 15% at ~ 570 nm. To analyze and design the light-emitting metasurface, a computationally efficient temporal coupled-mode theory (CMT) framework is employed, explicitly adapted to organic dye gain media and accounting for the critical reabsorption effect.

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