Abstract

During the last twenty years high resolution spectroscopy in the 10 µm spectral region has reached a resolution at the level of the kHz [1]. The CO₂ laser locked onto a saturated absorption resonance of O_SO₄ provides a secondary frequency standard in the 10 µm region, with a reproducibility of the order of 10^–13 for the strongest lines [1]. To improve this performance the well-known strategy is to develop narrower and narrower references which are presently about 10 kHz wide; since most of the systematic errors are proportional to the linewidth of the frequency reference, any increase in the experimental resolution will result in an increase of the ultimate accuracy of the frequency standard.

© 2000 IEEE