To meet the light source requirement for image positioning of the lightning imager on board the Fengyun-4 meteorological satellite, a laser with a central wavelength of 777. 4 nm and a continuous output power of 1. 5 W is designed based on a two-stage master oscillation power amplifier structure (MOPA) and a periodically polarized lithium niobate crystal doped with magnesium oxide (MgO: PPLN) to double the frequency. Using 940 nm off-peak pumping technology to suppress the amplified spontaneous emission (ASE) and stimulated Brillouin scattering (SBS) in the optical amplifier, we obtain a single-frequency narrow linewidth laser with an output power of 15 W, a signal-tonoise ratio of 59. 6 dB, a linewidth of 323. 4 kHz, and a relative intensity noise of -145 dBc/ Hz. The optical-optical conversion efficiency of the amplifier is up to 37. 2%. Based on the theoretical analysis of the doubling efficiency, temperature-tuned bandwidth, and acceptable wavelength bandwidth of the MgO: PPLN crystal used, 777. 4 nm continuous light with a power of 1. 5 W is obtained using a single-pass doubling method.