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Sum frequency generation of sodium resonance radiation.

We have generated pulsed, high power, sodium resonance radiation by sum frequency mixing the 1.06 microm and 1.32 microm outputs of two Nd:YAG lasers with an average power conversion efficiency of 30%. The wavelength of the sum radiation was tuned across the full Doppler width of the sodium-vapor D(2) absorption by tuning the wavelength of either Nd:YAG laser with intracavity etalons. The wavelength of the 1.32 microm Nd:YAG laser was also tuned by injection seeding with a GaInAsP/InP diode laser. We have used this sodium resonance radiation for the lidar observation of the earth's naturally occurring atomic-sodium layer at 90 km altitude.