Power scaling of the self-frequency-doubled quasi-two-level Yb:YCOB laser with a 30% slope efficiency.

The lab-on-chip integration of photonic devices has been attracting increasing attention recently. Multifunctional materials provide natural platforms for the desirable performance by the coupling of different functionalities. The insufficient coupling efficiency of the laser and nonlinear processes in self-frequency-doubled (SFD) lasers is the limiting factor for the output power and further practical applications. Here we demonstrate a SFD Yb ³⁺ -doped calcium yttrium oxoborate (Yb:YCOB) crystal laser with an unprecedented slope efficiency of 30% and output power of 6.2 W at 513 nm. The successful realization of this laser operating in a quasi-two-level configuration is based on enhanced coupling of the laser and frequency-doubling processes using a monolithic configuration, benefiting from an ultimately small laser quantum defect, the anisotropic gain cross sections, and the high effective nonlinearity of the monoclinic YCOB outside the principal planes. Solid-state lasers in the spectral range around 510 nm are scarce, and the results not only present a significant advancement in the field of SFD lasers, but also pave the way for future applications of such green lasers, especially in areas such as medical treatment, daily life, and scientific investigations.