DOPPLER-FREE 2-PHOTON SPECTROSCOPY OF HYDROGEN RYDBERG STATES USING A CW LASER

The 8 S// one-half and 8 D//J states of atomic hydrogen are excited using Doppler-free two-photon absorption from the metastable 2 S state. Using an atomic beam of metastable 2 S// one-half atoms collinear with the counterpropagating laser beams, we measure a relative linewidth of 4 multiplied by 10** minus **9. This linewidth is presently the smallest that has been observed in an optical transition in atomic hydrogen. The 2 S// one-half -8 D//5/////2 isotope shift of hydrogen and deuterium is measured: DELTA equals 209692. 2 plus or minus 2. 2 MHz.