Magnetically-induced Transitions Research Articles

Application of magnetically induced [formula omitted] atomic transitions of cesium atoms in strong magnetic fields

In this work, magnetically induced (MI) transitions of the Cs atoms in strong magnetic fields up to 6 kG, and their applications in spectroscopy are studied experimentally and theoretically. An attractive feature of these transitions is their large frequency shift slope in a magnetic field (−4 MHz/G). Therefore, in strong magnetic fields the frequency shift of MI transitions reaches several tens of GHz and importantly, these transitions do not overlap with others, which is of practical interest for possible use in new frequency ranges. To implement the process of electromagnetically induced transparency (EIT) in a strong magnetic field (1–2 kG), the MI Fg=4→Fe=2 transitions were first used at the frequency of probe radiation, while the frequency of coupling radiation is resonant the Fg=3→Fe=2 transitions. To form the EIT resonance, a cell of sub-micron thickness filled with Cs atom vapors was used, along with strong permanent magnets.

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

Atomic transitions satisfying Fe−Fg=ΔF=±2 (where Fe stands for excited and Fg 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 σ+ (ΔmF=+1) MI transitions Fg=3→Fe=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 Fg=4→Fe=5σ+ 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 D2 line transition wavelength. Due to the large frequency shift slope of the MI transitions (∼ 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 ∼ 3 kG. Preliminary calculations performed considering Doppler-broadened three level systems in a nanocell are in reasonable agreement with the experimental measurements.

Effect of Buffer Gas Influence on Magnetically-Induced Transitions in 87Rb Atoms, D2 Line

Effect of Buffer Gas Influence on Magnetically-Induced Transitions in 87Rb Atoms, D2 Line

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

The probabilities of atomic transitions F e − F g = ± 2 between a ground F g and an excited F e level of the D 2 line of any alkali metal atom are zero when no external magnetic field is applied. In an external magnetic field in the range of 0.1–3 kG, the probabilities of these transitions called magnetically induced (MI) are highly modified. For MI transitions, we previously exhibited the following rule: the probabilities of MI transitions with Δ F = + 2 are maximal when using σ + -polarized laser radiation, while the probabilities of MI transitions with Δ F = − 2 are maximal when using σ − -polarized laser radiation. This difference has been termed type 1 MI circular dichroism. It is demonstrated for the first time, to our knowledge, that for alkali atoms with a nuclear spin I = 3 / 2 ( 87 R b , 39 K , 23 N a , 7 L i ) in magnetic fields > --> 100 G , the probability of the strongest σ + MI transition of the group F g = 1 → F e = 3 ′ (transition | 1 , − 1 ⟩ → | 3 ′ , 0 ′ ⟩ ) is about four times higher than the probabilities of the strongest MI σ − -transitions | 1 , − 1 ⟩ → | 3 ′ , − 2 ′ ⟩ and | 2 , + 1 ⟩ → | 0 ′ , 0 ′ ⟩ . These properties make the σ + MI transition | 1 , − 1 ⟩ → | 3 ′ , 0 ′ ⟩ an interesting candidate for the study of magneto-optical processes in strong magnetic fields.

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 behavior of alkali transitions when placed in a magnetic field. Particularly, the probabilities of transitions obeying an apparent Fe−Fg≡ΔF=±2 selection rule, referred to as magnetically-induced (MI) transitions, 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 Λ-systems involving ΔF=−2 MI transitions, is only possible when both the coupling and probe beams are σ−-circular polarized, demonstrating that EIT is affected by magnetic circular dichroism. A similar rule of thumb can be extrapolated for ΔF=+2 MI transitions and σ+ 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.

Magnetically induced transition in the spectrum of Sr iv

Observations and studies of what we call magnetic induced transitions have arguably re-opened a whole new area of atomic spectroscopy. There are transitions from upper levels that are sensitive to externally applied magnetic fields, such as those in tokamaks and the solar corona. So far only two types of ionic systems have been confirmed as leading to magnetic induced transitions, namely Ne-like Ar and Fe, and Cl-like Fe. We here propose a homologous system to Cl-like ions, namely Br-like ions, as a new candidate. These transitions are fed by close degeneracy between levels of relative short and long lifetimes, respectively. A similar close degeneracy as in Cl-like Fe is present in Br-like Sr and will give rise to an observable magnetic induced transition. We have predicted the magnetic induced transition rate for the ${}^{4}{D}_{7/2}$ level in Sr iv as a function of magnetic field strengths.

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

Atomic transitions of alkali metals for which the condition Fe−Fg=±2 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 ΔF=±2 are maximum when using respectively σ± radiation. Within the same ground state, the difference in intensity for σ+ and σ− 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 σ+ and σ−, the probability of MI transition with ΔF=+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 D2 line; similar results are expected with other alkali metals. Theoretical calculations are in excellent agreement with the experimental measurements.

“Unmoved” Atomic Transitions of Alkali Metals in External Magnetic Fields

The “mixing” of magnetic sublevels of the ground and excited levels of an atomic transition with magnetic sublevels of a nearby transition (in the hyperfine structure of atoms of alkali metals) is responsible for a strong modification of its probability. A dramatic manifestation of this mixing effect is a huge increase in the probability of the atomic transition in magnetic fields that is forbidden by selection rules in zero magnetic field B = 0; the latter is called a magnetically induced (MI) transition. Two MI transitions with different dependences on B have been studied. Another dramatic manifestation of the mixing effect is that there are atomic transitions whose frequency is practically fixed in a wide range of magnetic fields, i.e., the slope S [MHz/G] of the frequency shifts as a function of B is practically zero, with the transition probability being significant. We call these transitions “unmoved” transitions (UTs). We have studied the UTs of 87Rb atoms, the D2 line, |1, +1〉 → |1', +1'〉 and Cs atoms, the D2 line, |3, –3〉 → |5', –4'〉, where the quantum numbers F and mF of the excited and ground levels are marked with and without primes, respectively. We show that in the range B = 180–705 G for 87Rb, the D2 line, |S| ≤ 0.03 MHz/G; for comparison, S ≈ 3.6 MHz/G for 87Rb in the same B range for the MI transition |1, +1〉 → |3', +2'〉 is greater by a factor of 120. A second laser was used to control the UT amplitude. Our theoretical model describes well the experiment.

SUMER Measurement of the Fe x 3p 43d 4D5/2,7/2 Energy Difference

Abstract Recent studies have shown that magnetic fields in the solar corona are strong enough to significantly mix the two 3p 43d 4D5/2,7/2 levels in Cl-like Fe x. This mixing gives rise to a magnetically induced transition (MIT) component in the bright Fe x 257.3 Å line, commonly observed by current instrumentation, that can be used for coronal magnetic field diagnostics. This line, commonly observed by the still operational EIS spectrometer on board the Hinode satellite since 2007, opens a new window into the coronal magnetic field. However, the strength of this MIT transition depends on the square of the energy difference ΔE of the two levels, so that an accurate determination of ΔE is of critical importance to accurately measure coronal magnetic field strengths. In the present work we present a new measurement of ΔE obtained determining the separation of the two component of the Fe x doublet close to 1603.3 Å from deep-exposure spectra of a quiescent streamer at the solar limb taken with the SUMER instrument on board SoHO. Our measurement of ΔE = 2.29 ± 0.50 cm−1 agrees with, and improves upon, an earlier measurements by Judge et al. by decreasing its uncertainty from 80% to approximately 20%, improving the attainable accuracy of magnetic field strength measurements obtainable with the Fe x 257.26 Å line.

Application of Magnetically Induced Transitions of 87Rb Atoms in Coherent Optical Processes

We experimentally demonstrated that magnetically induced (MI) Fg = 1 → Fe = 3 transitions of the D2-line of 87Rb are promising for the generation of optical resonances in strong magnetic fields of up to 3 kG. A cell of micron-scale thickness filled with Rb vapors was used. A simple and convenient method of determining magnetic induction that exhibits micron-scale spatial resolution is described. In the process, it becomes unnecessary using a reference spectrum. The probability of an MI transition in the interval of magnetic fields from 0.3 to 2 kG can exceed the probability of an ordinary atomic transition, which makes using it as a coupling or probe transition in Λ- or V-systems advantageous for formation of dark resonances in processes of electromagnetically induced transparency (EIT). Dark resonances shifted in strong magnetic fields by as much as 10 GHz may find a number of practical applications. Note that dark resonances are nearly absent in Λ-systems based on ordinary atomic transitions in magnetic fields exceeding 1 kG.

Применение магнито-индуцированных переходов в атомах -=SUP=-87-=/SUP=-Rb в когерентных оптических процессах

The prospects of using Fg = 1-Fe = 3 magnetically induced (MI) transitions of the 87Rb D2 line to form optical resonances in strong magnetic fields up to 3 kG have been experimentally demonstrated. A micrometer-thick cell filled with the Rb atomic vapor is used. A simple and convenient method for determining the magnetic induction with a micron spatial resolution is presented. In this case, there is no need for a reference frequency spectrum. The probability of the MI transition in the magnetic field range of 0.3–2 kG may exceed the probability of a “normal” atomic transition; therefore, it is reasonable to use MI transition at the frequency of “coupling” or probe lasers in Lambda- and V systems to form EIT- resonance (also called dark resonance) in the process of electromagnetically induced transparency (EIT). The formation of dark resonances in strong magnetic fields, when there is a frequency shift of the dark resonance up to ~ 10 GHz, has a number of practical applications. Note that when using “ordinary” atomic transitions in the Lambda- system for magnetic fields of > 1 kG, dark resonances are practically absent.

Magnetically Induced Atomic Transitions of the Potassium D2 Line

Magnetically induced (MI) transitions of the D2 line of 39K atom in an external magnetic field of 10–600 G have been experimentally and theoretically investigated for the first time using circularly polarized σ+ and σ− radiations. According to the selection rules, the transitions between the sublevels of the ground and excited levels of a hyperfine structure with Fe – Fg = ΔF = ±2 are forbidden in the zero magnetic field, whereas their probabilities increase radically in a magnetic field. For the Fg = 1 → Fe = 3 (ΔF = +2) and Fg = 2 → Fe = 0 MI transitions, the highest probabilities are achieved using the σ+ and σ– radiations, respectively. The atomic transitions have been spectrally resolved using selective reflection of laser radiation from a nanocell filled with potassium atomic vapor, which makes it possible to investigate the behavior of the MI transitions. The experimental and theoretical data are shown to be in good agreement.

Магнитоиндуцированныe атомные переходы D-=SUB=-2-=/SUB=--линии калия

For the first time, magnetically induced (MI) transitions of the D2 line of the 39K atom in an external magnetic field of 10–600G using circularly polarized radiation σ + and σ – have been investigated. According to the selection rules in a zero magnetic field, transitions between sublevels of the ground and excited levels of the hyperfine structure with Fe - Fg = delta F = ± 2 are prohibited, while in the magnetic field there is a giant increase in their probabilities. For MI transitions, Fg = 1-> Fe = 3(delta F = +2) the highest probability is achieved when using σ+ radiation, and for Fg = 2->Fe = 0 the highest probability is achieved when using σ-  radiation. For the atomic transitions spectral separation the process of selective reflection of laser radiation from nanocell, filled with potassium atoms is used. This which allowed us to study the behavior of the MI transitions. The experiment well consistent with the theory.

Atomic lifetime measurements of Ne-like Fe ions in a magnetic field

Among the lowest excited levels in Ne-like ions, that is, of configuration 2p53s, there is a J=0 level that in a field-free environment decays by a magnetic dipole (M1) transition to the lower J=1 level of the same configuration only. In the presence of a magnetic field, this level can also decay to the ground configuration J=0 level. In the course of the first measurement of the 2p53s J=0 level lifetime and the M1 transition rate the magnetically induced transition (MIT) appeared as a complication that was then turned into a tool. The technical details of the measurement in an electron beam ion trap have been described elsewhere. Here we illuminate the physics aspects of the two transition rate measurements and show how the results compare to computations.