Observation of magnetically-induced transition intensity redistribution in the onset of the hyperfine Paschen-Back regime

The Zeeman effect is an important topic in atomic spectroscopy. The induced change in transition frequencies and amplitudes finds applications in the Earth-field-range magnetometry. At intermediate magnetic field amplitude $B\sim B_0 = A_\text{hfs}/\mu_B$, where $A_\text{hfs}$ is the magnetic dipole constant of the ground state, and $\mu_B$ is the Bohr magneton ($B_0\approx 1.7$ kG for Cs), the rigorous rule $\Delta F = 0, \pm1$ is affected by the coupling between magnetic sub-levels induced by the field. Transitions satisfying $\Delta F = \pm2$, referred to as magnetically-induced transitions, can be observed. Here, we show that a significant redistribution of the Cs $6\text{S}_{1/2}\rightarrow 6\text{P}_{3/2}$ magnetically-induced transition intensities occurs with increasing magnetic field. We observe that the strongest transition in the group $F_g=3\rightarrow F_e=5$ ($\sigma^+$ polarization) for $B<B_0$ cease to be the strongest for $B>3 B_0$. On the other hand, the strongest transition in the group $F_g=2\rightarrow F_e=4$ ($\sigma^-$ polarization) remains so for all our measurements with magnetic fields up to 9 kG. These results are in agreement with a theoretical model. The model predicts that similar observations can be made for all alkali metals, including Na, K and Rb atoms. Our findings are important for magnetometers utilizing the Zeeman effect above Earth field, following the rapid development of micro-machined vapor-cell-based sensors

Magnetic field--induced modification of selection rules for Rb D2_2 line monitored by selective reflection from a vapor nanocell

Magnetic field-induced giant modification of the probabilities of five transitions of $5S_{1/2}, F_g=2 \rightarrow 5P_{3/2}, F_e=4$ of $^{85}$Rb and three transitions of $5S_{1/2}, F_g=1 \rightarrow 5P_{3/2}, F_e=3$ of $^{87}$Rb forbidden by selection rules for zero magnetic field has been observed experimentally and described theoretically for the first time. For the case of excitation with circularly-polarized ($\sigma^+$) laser radiation, the probability of $F_g=2, ~m_F=-2 \rightarrow F_e=4, ~m_F=-1$ transition becomes the largest among the seventeen transitions of $^{85}$Rb $F_g=2 \rightarrow F_e=1,2,3,4$ group, and the probability of $F_g=1,~m_F=-1 \rightarrow F_e=3,~m_F=0$ transition becomes the largest among the nine transitions of $^{87}$Rb $F_g=1 \rightarrow F_e=0,1,2,3$ group, in a wide range of magnetic field 200 -- 1000 G. Complete frequency separation of individual Zeeman components was obtained by implementation of derivative selective reflection technique with a 300 nm-thick nanocell filled with Rb, allowing formation of narrow optical resonances. Possible applications are addressed. The theoretical model is perfectly consistent with the experimental results.Comment: 6 pages, 5 figure

Etudes des processus optiques et magnéto-optiques dans des couches atomiques minces nanométriques de potassium, rubidium et césium

It has been investigated the D1 line transitions of 39K atoms in external magnetic fields using nanocells for the cases of sigma+ and pi polarizations of laser radiation. For the first time it is demonstrated the decoupling of electronic total angular momentum J and nuclear momentum I (complete hyperfine Paschen-Back regime) in external magnetic field. For 39K the decoupling takes place at B >> 165 G. In the case of linear polarization it is shown that for B > 400 G the transmission spectrum consists of 2 groups of transitions and each group contains of one so-called "Guiding transition" (GT). The GT indicates the asymptotic value of all transitions probabilities in the group and the frequency shifts derivatives value (frequency slopes) in magnetic field.For the first time it is demonstrated the absence of cross-over resonances in the spectrum of saturated absorption. For that Rb filled micro-cell has been used with atomic vapor thickness 30-40 µm. The use of micro cell allowed the investigation of individual atomic transitions in strong external magnetic fields 30 - 6000 G ) using the saturated absorption technique. It is experimentally and theoretically manifested that at certain values of the external magnetic fields (300 - 2000 G) the probabilities of the Cs D2 line Fg=3 --> Fe=5 atomic transitions experience huge increase. These probabilities, which are forbidden at zero magnetic field, exceed the probabilities of allowed atomic transitions.Les transitions D1 d'atomes 39K confinées en nano-cellule, soumis à des champs magnétiques externes ont été étudiées dans les cas de polarisation sigma+ et pi de la radiation laser. Il est montré, pour la première fois, le découplage du moment angulaire total J et du moment nucléaire I (régime Paschen-Back hyperfin) sous champ magnétique externe. Le découplage se produit pour un champ B >> 165 G. Dans le cas d'une polarisation linéaire du laser, nous montrons que pour B > 400 G, le spectre de transmission consiste en 2 groupes de transitions et chaque groupe contient une transition appelée transition guide (GT). La GT indique la valeur asymptotique des probabilités des transitions dans un groupe et la valeur des dérivées des décalages en fréquence (pentes de fréquence) dans un champ magnétique.Pour la première fois, il est montré l'absence de résonances cross-over dans le spectre d'absorption saturée. Nous avons utilisé des micro cellules remplies de rubidium. L'épaisseur de la colonne de vapeur atomique était de 30 - 40 micromètres. L'utilisation d'une micro cellule a permis l'investigation des transitions atomiques individuelles dans des champs magnétiques intenses (30 - 6000 G) en utilisant la technique d'absorption saturée. Nous avons aussi déterminé expérimentalement et théoriquement que pour certaines valeurs du champ magnétique externe (300 - 2000 G), on observait un très grand accroissement des probabilités des transitions atomiques Fg = 3 --> Fe = 5 de la raie D2 du Cs. Sous champ B, les probabilités de ces transitions (qui sont interdites en l'absence de champ magnétique) augmentent brutalement et excédent les probabilités des transitions atomiques permises

Dominant magnetically induced transitions in alkali metal atoms with nuclear spin 3/2

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Formation of strongly shifted EIT resonances using “forbidden” transitions of Cesium

Atomic transitions satisfying $F_e - F_g = \Delta F = \pm 2$ (where $F_e$ stands for excited and $F_g$ stands for ground state) of alkali atoms have zero probability in zero magnetic field (they are so-called "forbidden" transitions) but experience a large probabilty increase in an external magnetic field. These transitions are called magnetically induced (MI) transitions. In this paper, we use for the first time the $\sigma^+$ ($\Delta m_F~=~+1$) MI transitions $F_g = 3 \rightarrow F_e = 5$ of {Cesium} as probe radiation to form EIT resonances in strong magnetic fields (1 - 3 kG) while the coupling radiation frequency is resonant with $F_g=4\rightarrow F_e=5$ $\sigma^+$ transitions. The experiment is performed using a nanometric-thin cell filled with Cs vapor and a strong permanent magnet. The thickness of the vapor column is 852 nm, corresponding to the Cs $D_2$ line transition wavelength. Due to the large frequency shift slope of the MI transitions ($\sim$ 4 MHz/G), it is possible to form contrasted and strongly frequency-shifted EIT resonances. Particularly, a strong 12 GHz frequency shift is observed when applying an external magnetic field of $\sim$ 3 kG. Preliminary calculations performed considering Doppler-broadened three level systems in a nanocell are in reasonable agreement with the experimental measurements

Coherent optical processes on Cs D2 line magnetically induced transitions

The increased spectral resolution allowed by the use of extremely thin vapor cells has led to the observation of interesting behaviour of alkali transitions when placed in a magnetic field. Particularly, transitions obeying an apparent $F_e-F_g\equiv\Delta F =\pm2$ selection rule, referred to as magnetically-induced (MI) transitions, have their probabilities largely increase in the intermediate interaction regime while being null at zero and higher magnetic fields. With an 800 nm-thick Cs vapor cell placed in a field up to 1.5 kG, we show here that the generation of electromagnetically induced transparency (EIT), realized in $\Lambda$-systems involving $\Delta F =- 2$ MI transitions, is only possible when both the coupling and probe beams are $\sigma^-$-circular polarized, demonstrating that EIT is affected by magnetic circular dichroism. A similar rule of thumb can be extrapolated for $\Delta F =+2$ MI transitions and $\sigma^+$ polarization. Because of the high frequency shift slope (typ. 4 MHz/G), the generation of EIT resonances involving MI transitions is interesting, especially in the context of growing attention towards micro-machined alkali vapor cell sensors

Circular dichroism in atomic vapors: Magnetically induced transitions responsible for two distinct behaviors

Atomic transitions of alkali metals for which the condition $F_e-F_g = \pm2$ is satisfied have null probability in a zero magnetic field, while a giant increase can occur when an external field is applied. Such transitions, often referred to as magnetically-induced (MI) transitions, have received interest because their high probabilities in wide ranges of external magnetic fields which, in some cases, are even higher than that of usual atomic transitions. Previously, the following rule was established: the intensities of MI transitions with $\Delta F=\pm2$ are maximum when using respectively $\sigma^\pm$ radiation. Within the same ground state, the difference in intensity for $\sigma^+$ and $\sigma^-$ radiations can be significant, leading to magnetically induced circular dichroism (MCD), referred to as type-1. Here, we show that even among the strongest MI transitions, $i.e$ originating from different ground states for $\sigma^+$ and $\sigma^-$, the probability of MI transition with $\Delta F = + 2$ is always greater, which leads to another type of MCD. Our experiments are performed with a Cs-filled nanocell, where the laser is tuned around the D$_2$ line; similar results are expected with other alkali metals. Theoretical calculations are in excellent agreement with the experimental measurements.Comment: 17 pages, 7 figure