Sub-Doppler spectroscopy by sub-micron thin Cs vapour layer

A unique extremely thin cell (ETC) with the thickness of Cs atomic vapour layer in the range of 150–300 nm has been developed for the first time. All six hyperfine transitions of D₂ line (852 nm) of Cs, i.e. 6S_1/2(F=3)→6P_3/2(F=2–4) and 6S_1/2(F=4)→6P_3/2(F=3–5) are very well resolved in the transmission and fluorescence spectra, whereas in a cell of usual length they are not resolved due to Doppler broadening. It is demonstrated that a robust and widely used simple laser-diode technique is enough to observe separately atomic hyperfine transitions at the intensity up to 100 mW/cm² thanks to the ETC usage. We report also the first results obtained with the new ETC of 300 nm thickness filled with natural Rb. The usage of ETC allowed us to completely resolve each particular hyperfine transition of both ⁸⁵Rb and ⁸⁷Rb isotopes in D₁ line fluorescence spectrum.