PECULIARITIES OF RESONANT ABSORPTION AND FLUORESCENCE IN EXTREMELY THIN CELL FILLED WITH Rb AND BUFFER GAS.
Résumé
Recently unique extremely thin cells (ETC) containing atomic vapour of alkali metals with the column thickness L of an order and much less than optical light wavelength λ have been developed. It has been demonstrated that these ETC are a very promising tool for a fundamental study of atom-light, atom-atom, atom-surface and atom-external magnetic field interactions. Particularly, a dramatically different behaviour of resonant absorption, fluorescence and resonant magneto-optical processes compared to that obtained with the help of cm-long ordinary cells has been demonstrated. Possible applications based on ETC are described, such as magnetometers with nanometric spatial resolution and tunable atomic frequency references. For the study of buffer gas influence, a multi-region cell (MRC) has been developed. MRC consists of an ETC cell having a wedged thickness of the gap between the windows that allows one to form atomic vapour column thickness in the range of 0.1 ÷ 4 μm. The ETC is connected through a sapphire tube with a 1cm-long sapphire tube having sapphire windows. The 1cm-long cell has a sapphire side-arm containing Rb metal. MRC's are filled with 6 Torr and 20 Torr Neon gas, thus there is Rb vapour and buffer gas inside the MRC. The construction of the MRC allows one to compare absorption and fluorescence processes simultaneously in the case of the ETC use as well as in the case of 1cm-long ordinary cell use. The comparison of the resonant absorption and fluorescence in the extremely thin cell (ETC) filled with pure Rb with another one filled with Rb and Neon gas with the pressures of 6 Torr and 20 Torr is provided. The effect of the collapse and revival of Dicke-type narrowing is still observable for the thicknesses L = λ/2, and L = λ, with λ being the resonant laser wavelength 794 nm (D1 line of Rb), i.e. the spectra of the resonant absorption and fluorescence demonstrate strong sub-Doppler narrowing for the thickness L = λ/2 and broadening for the thickness L = λ. It is important to note that in an ordinary Rb cell with the thickness L in the range of 1mm - 10 cm filled with buffer gas, with the pressure higher than 1 Torr, in the well-known Saturation Absorption scheme, any sub-Doppler features are absent. For L = λ the so called velocity selective optical pumping/saturating resonance (VSOP) located at the atomic transition is still observable when Ne pressure is 6 Torr, while the linewidth is increased by 4 times in comparison with that obtained in a pure Rb ETC. It is also demonstrated that the use of the fluorescence spectra at L = λ/2 allows one to use ETC for the buffer gas pressure measurements. Comparison with the theory will be presented.