PHOTON-ECHO IN MOLECULAR GASES .3. COHERENT DOPPLER-FREE SPECTROSCOPY

This paper provides a review of experiments on coherent high-resolutio n Doppler-free spectroscopy of low-pressure molecular gases. We analyz e advantages of coherent Doppler-free spectroscopy over saturated-abso rption spectroscopy associated with the increase in the signal-to-nois e ratio by several orders of magnitude and the absence of power broade ning. A method for the detection of homogeneously broadened lines with in a Doppler contour based on the phenomenon of photon echo in standin g waves is proposed and implemented. The developed method is employed to resolve the fine structure of a vibrational-rotational transition i n SF6. The possibility of applying methods of coherent spectroscopy fo r obtaining high-contrast spectral reference lines is discussed. The r esults of studies devoted to the selection of slow molecules with the use of coherent transient processes are presented. The prospects for e mploying slow molecules for the investigation of interactions between slow molecules and for the purposes of high-resolution spectroscopy ar e analyzed.