High resolution laser spectroscopy with minute samples

A technique is described which enables high resolution measurements to be made, using a c.w. tunable dye laser, with atomic beam fluxes as low as 10 atoms/s, corresponding to a spatial density of about 0.2 atoms/cm³. The burst of resonantly scattered light, occuring as each atom crosses the laser beam, is recorded. Detected bursts of 3 photoelectron pulses, or more, show significant improvements in peak to background ratios. Results for Na (5890 Å) and Ba (5535 Å) are discussed. In both cases, the experimental resolution is determined by the natural linewidths of the transitions.