OPTICAL RAMSEY SPECTROSCOPY OF ATOMIC-HYDROGEN

We report the observation of optical Ramsey fringes on the two-photon 1S-2S transition in atomic hydrogen with a pulsed temporal excitation scheme. With this technique we have improved the spectral resolution o f this transition to a linewidth of 800 Hz at 243 nm, corresponding to 6 parts in 10(13), setting a new record for neutral atoms. By applyin g a large number of light pulses we observe sharply peaked lines in th e spectrum rather than the sinusoidal pattern obtained with two excita tion pulses.