Sub-Doppler absorption resonances of three-level quantum systems in thin gas cells

Interaction of probe and pump monochromatic waves is analyzed with the Lambda-system of three quantum levels of atoms (molecules) in the thin gas cell, whose length is much less than the diameter of light beams. Nontrivial peculiarities were discovered of sub-Doppler absorption resonances, caused by the light-induced coherence of lower long-lived quantum states of the. Lambda-system. Given resonances may be used for the stabilization of both frequencies of waves and the difference of these frequencies.