High-repetition-rate pulsed electron source based on an atomic Rydberg photocathode

A gas of rubidium atoms has been excited by a combination of ultraviolet an d far-infrared excitation to a superposition of Stark states lying just abo ve the classical saddle paint. Using an atomic streak camera, we have demon strated that the atom ejects an ultrafast train of electron subpulses nearl y equally spaced in time, with a repetition rate of approximately 50 GHz. T he frequency characteristics of this pulse train are seen to be extremely s ensitive to small changes in the static electric field. These measurements imply that, by variation of the electric field during the electron emission , it is possible to create shaped ultrafast electron pulses analogous to sh aped optical pulses. (C) 1999 Optical Society of America [S0740-3224(99)001 01-0] OCIS codes: 020.0020, 020.5780, 320.5390, 320.7080, 320.1100, 320.032 0.