Abstract

We present an ultrahigh-resolution saturation spectrometer based on a line-tunable carbon monoxide laser near 60 THz $\left(\lambda =5 \mu \mathrm{m}\right)$. A spectral resolution of 14 kHz $\left(\mathrm{\Delta }\nu /\nu =2.3\times {10}^{-10}\right)$ for CO fundamental-band transitions was achieved, which improves on earlier results by one order of magnitude. A frequency-locking scheme using tunable microwave sidebands provides tunability and absolute frequency control of the CO laser on the kilohertz. Transit-time broadening and pressure broadening of the observed transitions are significantly reduced by use of expanded laser beams in a 24-m absorption cell at pressures down to 0.01 Pa. The new spectrometer is suitable for the study of saturation line shapes and the development of a new generation of frequency standards in the 60-THz region.

© 2001 Optical Society of America

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