On super-high resolution spectroscopy of metastable atoms in ultra-thin gas cells

It was theoretically investigated narrow sub-Doppler resonances in the spectral distribution of a number of atomic particles optically excited in a metastable state in an ultra-thin 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. Thus the regime of coherent Rabi oscillations was considered on the light induced transition from the ground atomic term to the metastable quantum level on the basis of atomic density matrix equations. It was analyzed the essential dependence of sub-Doppler resonances (on the center of the optical transition) on the inner thickness and transversal size of a thin gas cell (having the shape of the rectangular parallelepiped) and also on the intensity of the laser radiation. There were suggestions about schemes of possible record of these resonances by methods of absorption, fluorescence and photoionization spectroscopy with use of an additional probe radiation. Investigated resonances may be applied as references in high-accuracy optical frequency standards and for high precision measurements of central frequencies of atomic spectral lines