Optical pumping methods have been extended to high buffer-gas pressures by replacing the customary resonance lamp by a white-light source. Rb ground-state Zeeman transitions were detected by resonance fluorescence at argon buffer-gas pressures up to 23 atm. Hyperfine-transition frequencies were measured at 4170 Torr (0°C) and at 7390 Torr (0°C) and showed the first nonlinear pressure dependence so far observed.

• Received 22 May 1969

DOI:https://doi.org/10.1103/PhysRevLett.22.1349