2S-nS and 2S-nD transitions
ExperimentThe experiments we have performed between 1985 and 2000 on the 2S-nS and 2S-nD transitions in atomic hydrogen are described below with their main results.
Hydrogen atoms in 2S metastable state are produced by electronic impact in an atomic beam [Biraben et al 1990]. They are excited towards nS or nD (n = 6 to 12) state by two-photon excitation with a colinear laser beam. We use a home-made titanium-sapphire laser delivering about 1 W in the range 750-820 nm. The metastable atomic beam is placed inside an enhancement cavity in order to increase the excitation light power and cancel the first-order Doppler effect. The colinear geometry also reduces the transit time broadening of the lines. The number of remaining metastable atoms is measured at the end of the atomic beam : an electric field quenches the 2S state and two photomultipliers detect the 2P-1S fluorescence. The transition signal is given by the decrease of the 2S population when the laser frequency is swept across the resonance [Garreau et al 1990].