Abstract

Many laboratories have developed IR frequency measurement techniques, particularly for the determination of the 88-THz He–Ne/CH₄ laser frequency. Disagreements of the order of 10⁻¹⁰ remain between various values, which can be explained by the gas laser effect, the residual Doppler effect, and the hyperfine structure of the F₂(2) methane line. Other laboratories, particularly in the U.S.S.R., have developed better lasers allowing the resolution of the F₂(2) line or operation with the E line of methane. At the LPTF we have developed stabilized CO₂ lasers by saturated absorption with OsO₄ in an external Fabry-Perot cavity; they have a reproducibility of 2–3 × 10⁻¹³ and an accuracy of 2 × 10⁻¹²; furthermore, they can be measured with an uncertainty limited by their accuracy. These CO₂/OsO₄ frequency standards are particularly useful for near-IR and visible frequency measurements.

© 1987 Optical Society of America