A simple and efficient scheme based on one-dimensional nanometric thin cell filled with Rb and strong permanent ring magnets allowed direct observation of hyperfine Paschen-Back regime on D 1 line in 0.5 − 0.7 T magnetic field. Experimental results are perfectly consistent with the theory. In particular, with σ + laser excitation, the slopes of B-field dependence of frequency shift for all the 10 individual transitions of 85,87 Rb are the same and equal to 18.6 MHz/mT. Possible applications for magnetometry with submicron spatial resolution and tunable atomic frequency references are discussed. c 2018 Optical Society of America OCIS codes: 020.1335, 300.6360Rubidium atoms are widely used in atomic cooling, information storage, spectroscopy, magnetometry etc [1,2]. Miniaturization of alkali vapor cells is important for many applications [3][4][5][6]. Atom located in magnetic field undergoes shift of the energy levels and change in transition probabilities, therefore precise knowledge of the behavior of atomic transitions is very important [7]. In case of alkali atomic vapor use a sub-Doppler resolution is needed to study separately each individual atomic transition between hyperfine (hf) Zeeman sub-levels of the ground and excited states (in case of a natural mixture of 85 Rb and 87 Rb the number of closely spaced atomic transitions can reach several tens). Recently it was shown that a one-dimensional nanometric-thin cell (NTC) with the thickness of Rb atomic vapor column L = λ, where λ = 794 nm is the wavelength of laser radiation resonant with D 1 line of Rb, is a good tool to obtain subDoppler spectral resolution. Spectrally narrow velocity- When NTC is placed in a weak magnetic field, the VSOPs are split into several components depending on total angular momentum quantum numbers F = I + J, with amplitudes and frequency positions depending on B-field, which makes it convenient to study separately each individual atomic transition.In this Letter we describe a simple and robust system based on NTC and permanent magnets, which allows of achieving magnetic field up to 0.7 T sufficient to observe a hyperfine Paschen-Back regime [9]. The magnetic field required to decouple the nuclear and electronic spins is given by B ≫ A hf s /µ B ∼ = 0.2 T for 87 Rb, and

Simple and efficient "λ-method" and "λ/2-method" (λ is the resonant wavelength of laser radiation) based on nanometric-thickness cell filled with rubidium are implemented to study the splitting of hyperfine transitions of 85 Rb and 87 Rb D1 line in an external magnetic field in the range of B = 0.5 − 0.7 T. It is experimentally demonstrated from 20 (12) Zeeman transitions allowed at low B-field in 85 Rb ( 87 Rb) spectra in the case of σ + polarized laser radiation, only 6 (4) remain at B > 0.5 T, caused by decoupling of the total electronic momentum J and the nuclear spin momentum I (hyperfine Paschen-Back regime). The expressions derived in the frame of completely uncoupled basis (J, mJ ; I, mI ) describe very well the experimental results for 85 Rb transitions at B > 0.6 T (that is a manifestation of hyperfine Paschen-Back regime). A remarkable result is that the calculations based on the eigenstates of coupled (F, mF ) basis, which adequately describe the system for low magnetic field, also predict reduction of number of transition components from 20 to 6 for 85 Rb, and from 12 to 4 for 87 Rb spectrum at B > 0.5 T. Also, the Zeeman transitions frequency shift, frequency interval between the components and their slope versus B are in agreement with the experiment.

We describe analytically and numerically the process of population transfer by stimulated Raman adiabatic passage through a bright state when the pulses propagate in a medium. Limitations of the adiabaticity are analyzed and interpreted in terms of reshaping of the pulses. We find parameters for the pulses for which the population transfer is nearly complete over long distances.