The high power single frequency laser at 507.4nm is proposed based on the high efficient frequency doubling technology of a 1014.8nm room-temperature fiber laser amplifier.High efficient frequency doubling is realized in a high gain ring cavity with a normal incidence lithium triborate crystal.The double frequency efficiency is up to 61.5% and the output power is up to 3 W.The experimental data and simulated results of the input-output characteristics of the frequency doubling are coincide.The double freque...