Low‐Threshold Whispering‐Gallery Mode Upconversion Lasing via Simultaneous Six‐Photon Absorption

Abstract The upconversion lasing through simultaneous multiphoton absorption (MPA) is a high‐order nonlinear optical process, which enables many critical applications in the fluorescence imaging probe, laser tomography, and photodynamic therapy. Herein, the upconversion lasing from microwires via simultaneous six‐photon absorption at room temperature is first realized. Moreover, the lasing peak and third‐harmonic generation peak of pumping light are observed concurrently, while the temperature‐dependent spectrum elucidates the essential distinction between each other. In addition, the low‐threshold six‐photon excited whispering‐gallery mode lasing based on strong optical confinement of the hexagonal microcavity is investigated comprehensively. The results prove that it is feasible to realize high‐order MPA upconversion lasing using high Q‐factor microcavity, which can be promoted to other wide bandgap semiconductor micro‐/nanostructure to generate frequency upconversion lasing.