We describe the so-called "λ-Zeeman method" to investigate individual hyperfine transitions between Zeeman sublevels of atoms in an external magnetic field of 0.1 mT ÷ 0.25 T. Atoms are confined in a nanocell with thickness L = λ, where λ is the resonant wavelength (794 nm or 780 nm for D1 or D2 line of Rb). Narrow resonances in the transmission spectrum of the nanocell are split into several components in a magnetic field; their frequency positions and probabilities depend on the B -field. Possible applications are described, such as magnetometers with nanometric spatial resolution and tunable atomic frequency references.
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
Magnetic field-induced giant modification of probabilities for seven components of 6S 1/2 (F g =3) 6P 3/2 (F e =5) transition of Cs D 2 line forbidden by selection rules is observed experimentally for the first time. For the case of excitation with circularly-polarized laser radiation, the probability of F g =3,m F =-3 F e =5,m F =-2 transition becomes the largest among 25 transitions of F g =3 F e =2,3,4,5 group in a wide range of magnetic field 200 -3200 G. Moreover, the modification is the largest among D 2 lines of alkali metals. A half-wave-thick cell (length along the beam propagation axis L=426 nm) filled with Cs has been used in order to achieve subDoppler resolution which allows for separating the large number of atomic transitions that appear in the absorption spectrum when an external magnetic field is applied. For B > 3 kG the group of seven transitions Fg=3 Fe=5 is completely resolved and is located at the high frequency wing of Fg=3 Fe=2,3,4 transitions. The applied theoretical model very well describes the experimental curves.
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.
In this letter we study magnetic circular dichroism in alkali atoms exhibiting asymmetric behaviour of magnetically induced transitions. The magnetic field B k induces transitions between ΔF = ±2 hyperfine levels of alkali atoms and in the range of ∼0.1-3 kG magnetic field, the intensities of these transitions experience significant enhancement. We have inferred a general rule applicable for the D2 lines of all alkali atoms, that is the transition intensity enhancement is around four times larger for the case of σ + than for σ − excitation for ΔF = +2, whereas it is several hundreds of thousand times larger in the case of σ − than that for σ + polarization for ΔF = −2. This asymmetric behaviour results in circular dichroism. For experimental verification we employed half-wavelength-thick atomic vapor nanocells using a derivative of the selective reflection technique, which provides a sub-Doppler spectroscopic linewidth (∼50 MHz). The presented theoretical curves well describe the experimental results. This effect can find applications particularly in parity violation experiments.
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