High Power Single-Frequency 976 nm Fiber Laser Source and its Frequency Doubling for Blue Laser Generation

Abstract

High power compact and robust single-frequency all-fiber laser sources operating at 9xx nm have attracted significant attention because they can be used in a variety of applications including high-brightness low-noise single-mode pumps for neodymium (Nd3+), ytterbium (Yb3+), or erbium (Er3+)-doped lasers and nonlinear frequency converters for visible and deep-UV laser generation, atom cooling, remote sensing, and spectroscopy. So far, several 100-W-level fiber laser sources operating at around 980 nm have been demonstrated with Yb3+-doped photonic crystal fibers. However, all these laser sources have broad bandwidths, which constrain their use in many applications where single-frequency lasers with very narrow linewidths and very low noises are required. High power single-frequency fiber lasers are generally achieved with master oscillator and power amplifier (MOPA). In this dissertation, single-frequency Yb3+-doped silica and phosphate fiber amplifiers at 976 nm were investigated and the obstacles to develop high power 976 nm fiber amplifiers were studied and analyzed. A power-scalable 976 nm single-frequency MOPA laser source was developed by using a custom-designed large-mode-area Yb3+-doped phosphate fiber for the second stage amplifier and over 10 W continuous-wave output with a polarization extinction ratio of 20 dB was obtained. Further power scaling of the 976 nm fiber amplifiers has been discussed. The frequency doubling of the 976 nm single-frequency fiber laser was also demonstrated with a magnesium-doped periodically-poled lithium niobate (MgO:PPLN) crystal and over 500 mW single-frequency laser at 488 nm was obtained with single-pass second harmonic generation.