An all-optical method to control the lasing modes of Er-doped random fiber lasers (RFLs) is proposed and demonstrated. In the RFL, an Er-doped fiber (EDF) recoded with randomly separated fiber Bragg gratings (FBG) is used as the gain medium and randomly distributed reflectors, as well as the controllable element. By combining random feedback of the FBG array and Fresnel feedback of a cleaved fiber end, multi-mode coherent random lasing is obtained with a threshold of 14 mW and power efficiency of 14.4%. Moreover, a laterally-injected control light is used to induce local gain perturbation, providing additional gain for certain random resonance modes. As a result, active mode selection of the RFL is realized by changing locations of the laser cavity that is exposed to the control light.

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We demonstrate, in this paper, the creation of a femtosecond green laser achieved from a MgO-doped periodically poled lithium niobate crystal pumped by a home-made Yb-doped MOPA laser system. With an incident fundamental average power of 2 W, 820 mW (41 nJ) is produced at 515 nm with pulse duration of ~540 fs, corresponding to conversion efficiency of 40%. The standard deviation of the 515 nm pulse-to-pulse intensity is calculated as 0.007 (normalized), and the average power keeps stable with a root-mean-square value of 0.18% in an eight hour measurement. The spectral characters of the green laser and laser-induced damage thresholds of the crystal are also investigated. This stable laser system provides a compact and portable laser source for two-photon photopolymerization application.

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