Continuous-wave visible laser by intracavity-doubled fiber laser

Abstract

A novel continuous-wave blue-green laser was developed by the second-harmonic generation of the emission from Yb doped gain fiber. The laser cavity consists of a fiber Bragg grating (FBG), a gain fiber, an aspheric lens, a dichroic mirror for output coupling of second harmonic, a periodically-poled LiNbO₃ (PPLN), and a high reflector. The intracavity-doubled fiber laser was pumped by a 580-mW, fiber pigtailed laser diode at 974 nm through the FBG. The Yb laser emission from the fiber end was focused onto the high reflector, providing optical feedback and forming the resonator. The PPLN was placed near the flat end mirror, where the waist is formed, in order to increase the fundamental intensity. The emission wavelength can be selected by changing the FBG within the bandwidth of the gain fiber. An FBGs for 1017.6 nm was selected for the experiment. Circulating power of the fundamental wave in the cavity was measured to be approximately 1500 mW when a 5% output coupler was placed instead of high-reflecting mirror. Stable output in excess of 30 mW at 508.8 nm was obtained. The optical-optical efficiency from the pump power to the visible output was about 5%. The fluctuation of the laser output power was less than 0.5% for more than 2 hours without a power feedback loop. The M2 value was measured to be 1.2. Wavelength-selectable lasers will be useful for applications including fluorescent microscopy, biological imaging, flow cytometry and spectroscopic analysis.