Barrier-discharge source of cold hydrogen atoms in supersonic beams: Stark effect in the 1s-2s transition

An intense source of cold hydrogen atoms in a supersonic beam is presented. H and D atoms are produced from pure samples of H-2 and D-2 using a barrier discharge near the orifice of a cryogenic pulsed valve. The atoms are entrained in the supersonic expansion of the precursor molecules and cool down to translational temperatures as low as similar to 15 mK. The II-atom density at a distance of 1.2 m from the valve orifice is estimated to be around 10(8) cm(-3). The mean velocity of the supersonic beam containing the H (D) atoms can be adjusted between 2600 and 1200 m s(-1) (between 1850 and 820 m s(-1)). The barrier discharge also produces H-n(+) and D-n(+) ions with n ranging from 2 to 8, which can be deflected off the beam by electric fields. The use of this H-atom source in spectroscopic measurements is demonstrated by an investigation of the Stark effect in the 1s-2s two-photon transition of H and D. A near-Fourier-transformlimited pulsed laser generating pulses of UV radiation of adjustable pulse length between 10 and 200 ns near 243 nm is used to record spectra with full resolution of the hyperfine structure in the s states, providing a textbook example of the Stark effect in the simplest set of near-degenerate states of one-electron atoms.