International intercomparison of the wavelength of iodine-stabilized lasers

The wavelengths of He-Ne lasers stabilized by saturated absorption in iodine and designed at BIPM, NPL, and PTB have been compared simultaneously by beat frequency measurements. The intention of the comparisons was to get experience about the reproducibility of differently designed lasers. All lasers were stabilized by third harmonic locking but with different electronic circuits. Among other effects, the reproducibility appears affected also by a modulation amplitude dependent shift of the laser frequency f. For a suitable range of modulation amplitudes the reproducibility of the four investigated lasers has been estimated to be ±4 × 10⁻¹¹ f.