Compact 10 mW all-solid-state 491 nm laser based on frequency doubling a master oscillator power amplifier laser diode

We report on continuous-wave blue-green light generation by direct frequency doubling a monolithically integrated master oscillator power amplifier laser diode in a potassium niobate (KNbO3) crystal. 10 mW of diffraction limited (M(2) less than or equal to 1.1) second-harmonic light at 491 nm is generated with a fundamental power of 760 mW incident on a 17 mm long crystal. The blue-green laser radiation is 100% polarised and single-longitudinal mode with a frequency linewidth of similar to 33 GHz corresponding to a coherence length of similar to 6 mm. The root-mean-square fluctuations of the second-harmonic output power is as low as O.1% and the power drift is less than 3% over six hours.