75%-efficiency blue generation from an intracavity PPKTP frequency doubler

Abstract We report on a high-efficiency 461 nm blue light conversion from an external cavity-enhanced second-harmonic generation of a 922 nm diode laser with a quasi-phase-matched KTP crystal (PPKTP). By choosing a long crystal ( L C  = 20 mm) and twice looser focusing ( w 0  = 43 μm) than the “optimal” one, thermal lensing effects due to the blue power absorption are minimized while still maintaining near-optimal conversion efficiency. A stable blue power of 234 mW with a net conversion efficiency of η  = 75% at an input mode-matched power of 310 mW is obtained. The intra-cavity measurements of the conversion efficiency and temperature tuning bandwidth yield an accurate value d 33 (461 nm) = 15 (±5%) pm/V for KTP and provide a stringent validation of some recently published linear and thermo-optic dispersion data of KTP.