Tunable far-infrared radiation from optically pumped potassium Rydberg transitions

The generation of tunable far-infrared radiation by the optical pumping of potassium metal vapor to the 13p Rydberg state is reported. Subsequent cascade by stimulated emission is measured at several wavelengths between 76 and 146 cm-1 with a conversion quantum efficiency of greater than 10%. Emission observed in this region are tuned up to 18 GHz by the application of a pulsed Stark field across a parallel-plate heat pipe. Cascade branching to the 11 d to 10 f transition at 146 cm-1 is observed which can be tuned up to 7 cm-1 in the device. Similar branching following excitation up to the 18 p state is shown to provide almost complete tunability in the far-infrared region