Ultra-Low Threshold Single-Mode Upconversion Lasing in a Strong Coupled Microcavity via Four-Photon Absorption

With the development of ultra-fast optical technology, the nonlinear interaction between light and matter has attracted great attention. Upconversion laser generation through multiphoton absorption (MPA) enables numerous critical applications such as quantum signal processing, biophotonics, and 3D microfabrication. Herein, an ultra-low threshold single-mode four-photon absorption (4PA) upconversion lasing at room-temperature (RT) by constructing a strong-coupling microcavity is demonstrated. The planar microcavity significantly enhances the 4PA nonlinear interaction, which facilitates the obtainment of low-threshold upconversion lasing with an excellent output divergence angle and beam quality. In addition, the temporal dynamic mechanism and polarization characteristics of single-mode upconversion lasing are also comprehensively discussed. The work provides a feasible approach to fabricate a low-threshold single-mode upconversion laser through high-order nonlinear MPA processes.