The paper is the review of methods, achievements, and possibilities of the recently elaborated and well tested high-resolution
laser spectroscopy based on sub-Doppler absorption and polarization resonances (on centers of quantum
transitions), which arise because of the optical pumping and specific transit relaxation of atoms (molecules) in a thin cell
with a rarefied gas. Theoretical basis of this spectroscopy is presented. Experimental technique and results on the record
of the sub-Doppler spectral structure of Cs and Rb atoms and on the frequency stabilization of diode lasers by given
spectroscopy methods are discussed.
The possibility of the high-selective photoexcitation of molecules of a gas medium is shown on the basis of the coherent population trapping of sublevels of the ground term at the optical pumping by the two-frequency laser radiation. Such photoexcitation may be used in the technology of the isotope (isomer) separation, photochemistry and molecular biology, even in cases of comparatively dense media, when the selectivity has few of the usual methods of the laser action.