Reproducibility of Helium-Neon Laser Wavelengths at 633 nm

Measurements, performed at NBS, NPL, and PTB, on helium-neon lasers stabilized on the Lamb dip, have shown that the wavelengths of these lasers fell within approximately 1 part in 107. Beyond this limit, different lasers were found to emit different wavelengths. In addition, the wavelength of a given laser may vary during the life of its discharge tube. Pressure shifts appear to be a major cause of these variations. 1