The laser absolute wavelength standard problem

Stabilized lasers usually exhibit systematic frequency shifts larger than their resettability; this phenomenon is well illustrated by the 6328-Å helium-neon laser. We describe a Lamb-dip stabilized laser that operates at 1.15259 μ in pure low-pressure (0.12-torr) neon. Optical heterodyne experiments indicate an accuracy exceeding 1 part in 10⁹; short and medium term precisions of 1 : 10¹⁰are easily achieved. We also report the successful operation of a wavelength reference based on the saturation of sharp molecular absorption. In the first experiments the P(7) line of the v3band of methane is saturated inside the cavity of a 3.39-μ helium-neon laser. The saturation maximum at molecular line center produces an "emission" feature whose linewidth is less than 5 parts in 10⁹. The pressure-induced offset is expected to be less than 1 part in 10¹⁰. Size scaling is expected to improve these first results by at least 1 decade.