A potassium-mercury lamp in a sapphire envelope was constructed. Under the proper conditions of pressure and temperature the potassium resonance lines radiate efficiently at the infrared absorption lines of Nd3+in YAG. Spectral tests indicate that a threefold improvement in pumping efficiency should be obtained compared with a tungsten filament lamp. CW room-temperature laser tests result in an output of 10 watts for an input of 420 watts for a 2.4 percent overall efficiency. This compares with a 1 percent overall efficiency for the tungsten filament lamp.