Efficient Direct Laser Generation by Three‐Phonon‐Assisted Transition with Yb:YCOB Crystal

Electron–phonon‐coupling effect can generate the direct lasing beyond the fluorescence spectrum of the gain medium, but the laser efficiency is still low owing to weak multiphonon‐coupling intensity. Herein, associated with the three‐phonon‐assisted electron transitions beyond 1100 nm, the tunable laser generation from 1125 to 1155 nm and highly efficient continuous‐wave lasers at 1131 and 1140 nm in a ytterbium‐doped YCa 4 O(BO 3 ) 3 crystal are realized, by balancing the intracavity loss and phonon‐determined gain. The maximum output power reaches to 3.95 and 2.06 W at 1131 and 1140 nm, corresponding to a slope efficiency of 52.4% and 39.1%, respectively, which represents the highest efficiency in the solid‐state lasers in this spectral range. More impressively, this phonon‐assisted vibronic laser exhibits a wide‐spectral tunability and a good output power stability. Herein, a practical laser source in the underdeveloped spectral range is provided by the results, and they are helpful for the development of multiphonon‐assisted lasers beyond the inherent fluorescence spectrum.