2-micron solid state master oscillator and fiber power amplifier

Development of 2 micron solid-state lasers has attracted a great deal of attention in recent years, because 2 micron lasers have many potential applications in various fields, such as remote sensing, medical application, laser radar, and optical communication in space. The MOPA system is an effective way to obtain high energy and good frequency and beam qualities which are required in coherent lidars. The traditional MOPA systems use injection seeding technology to obtain narrow linewidth and high power/energy laser output at the same time. Feedback control makes systems of injection seeding MOPA more complicated in applications. Thanks to the fast development of fiber fabrication technology, various fibers working in 2 micron region are commercially available. Two micron fiber MOPA systems are more attractive for researchers due to their compactness, good thermal dissipation and high efficiency. A 2 micron master-oscillator-power-amplifier (MOPA) system was built. The seed oscillator was a plano-concave straight cavity. YAP Laser crystals with 4% and 5% thulium-doped concentration were used in our experiments. 1.5% and 3% output couplers were used. 442mW output power at 1.99μm was obtained with the 4% thulium-doped Tm:YAP crystal when the launched pumping power is 2.7W. The seed oscillator is coupled into a 4.5-meter-long double-cladding LMA Tm³⁺ and Al³⁺ co-doped fiber. The fiber diameter is 25 μm and NA is 0.1. 6.13W CW amplified output signal power was obtained when the launched pumping power was 60W.