title: Sub-Doppler spectroscopy of metastable atomic particles in ultrathin gas cells.
abstract: On the basis of density matrix equations, we theoretically investigated narrow sub-Doppler resonances in the spectral distribution of a number of atomic particles (atoms or molecules) optically excited in a metastable state in an ultrathin gas cell with the inner thickness less than or of the order of the wavelength λ ≤ 1 μm  of the monochromatic light wave incident in the normal direction. Essential dependence of these resonances (on the center of the optical transition) was analyzed versus the inner thickness and transversal size of such a gas cell and also versus the intensity of the incident wave. Investigated resonances may be applied as references in high-accuracy optical frequency standards and for high precision measurements.
authors.affiliation: Institute of Physics, Azerbaijan National Academy of Sciences, H. Javid av. 33, Baku, Az-1143, Azerbaijan. azizm57@rambler.ru
authors.forename: Azad Ch
authors.initials: ACh
authors.lastname: Izmailov
authors.forename: Chingiz O
authors.initials: CO
authors.lastname: Qajar
authors.forename: Ramiz A
authors.initials: RA
authors.lastname: Karamaliyev