Narrow 87Rb hyperfine-structure resonances in an evacuated wall-coated cell

Examination of 87Rb δF = 1, δ‖mF‖ = 1 hyperfine resonances in a 200-cm3 evacuated tetracontane wall-coated Pyrex cell which has been sealed since 1968 shows remarkable Dicke-narrowed sub-Doppler Lorentzian line shapes with less than 11 Hz full width. This linewidth is 70 times narrower than that in buffer gas filled cells used in commercial Rb atomic frequency standards. The phase shift per wall collision is 0.058 radians/collision as derived from an observed wall-induced hyperfine frequency shift of −52 Hz at a wall temperature of 26 °C.