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 Δ F = ± 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 D 2 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 Δ F = + 2 , whereas it is several hundreds of thousand times larger in the case of σ − than that for σ + polarization for Δ F = − 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.
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 Δ F = ± 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 D 2 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 Δ F = + 2 , whereas it is several hundreds of thousand times larger in the case of σ − than that for σ + polarization for Δ F = − 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.
Magnetic field-induced symmetry breaking exhibited by explicit circular dichroism for ΔF=±2 transitions of D2 lines of all alkali atoms
In this letter we demonstrate universal symmetry breaking by means of magnetically induced circular dichroism. Magnetic field induces forbidden at zero field atomic transitions between ΔF=±2 hyperfine levels. In a particular range of magnetic field, intensities of these transitions experience significant enhancement. We have deduced a general rule applicable for the D2 lines of all bosonic alkali atoms, that is transition intensity enhancement is larger for the case of σ+ than for σ− excitation for ΔF=+2, whereas it is larger (e.g. up to 1011 times for 85Rb atoms) in the case of σ− than for σ+ polarization for ΔF=−2. This asymmetric behaviour results in an explicit circular dichroism. For experimental verification we employed half-wavelength-thick atomic vapor nanocells using a derivative of selective reflection technique, which provides sub-Doppler spectroscopic linewidth ($\sim$50 MHz). The presented theoretical curves well describe the experimental results. This effect can find applications particularly in parity violation experiments.
Transitions F e − F g = Δ F = ±2 between the excited and ground levels of the hyperfine structure of the Cs D 2 atomic line in an external magnetic field of 300–3000 G have been studied for the first time with the use of σ + and σ − circularly polarized radiation. Selection rules forbid these transitions in zero magnetic field. At the same time, the probabilities of these transitions in a magnetic field increase significantly; for this reason, we refer to these transitions as magnetically induced transitions. The following rule has been found for the intensities of 24 magnetically induced F g = 3 → F e = 5 and F g = 4 → F e = 2 transitions: the intensities of magnetically induced transitions with Δ F = +2 are maximal (the number of such magnetically induced transitions is also maximal) in the case of σ + polarized radiation, whereas the intensities of magnetically induced transitions with Δ F = −2 are maximal (the number of such transitions is also maximal) in the case of σ − σ + and σ − polarized radiation can reach several orders of magnitude; i.e., anomalous circular dichroism is observed. For an experimental test, absorption spectra of a Cs-filled nanocell with the thickness equal to half the wavelength of resonant laser radiation = 852 nm have been analyzed in order to separately detect magnetically induced transitions. The experiment is in good agreement with the theory. Possible applications have been discussed.
Abstract The circular dichroism effect has been investigated for atomic transitions of the Rb D1 line in magnetic fields of up to 3 kG using circularly polarized σ+ and σ− radiation. The process of selective reflection from a 350-nm-thick nanocell has been used, which makes it possible to form narrow atomic lines and observe separately the behavior of individual transitions. Two groups consisting of six (85Rb atoms) and four (87Rb atoms) transitions are formed in magnetic fields B > 0.5 kG upon σ+ and σ− laser excitation. All transitions have been identified. It is shown that the strongest transitions for 87Rb and 85Rb atoms in magnetic fields of up to several kG are formed under σ− irradiation. A further increase in the magnetic field makes it possible to attain the Paschen–Back regime on a hyperfine structure, for which the probabilities of transitions upon σ+ and σ− excitation become identical. The theoretical model and experiment are in good agreement.
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 ⟩ → <m
Abstract 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.
Dark resonances were formed via electromagnetically induced transparency for the first time, to the best of our knowledge, involving magnetically induced ΔF=±2 atomic transitions of alkali metal atoms, which are forbidden at zero magnetic field. The probability of these transitions undergoes rapid growth when 300–3000 G magnetic field is applied, allowing formation of dark resonances, widely tunable in the GHz range. It is established that for ΔF=+2 (ΔF=−2) transition, the coupling laser tuned to ΔF=+1 (ΔF=−1) transition of the hyperfine Λ-system must be σ+ (σ−) polarized, manifesting anomalous circular dichroism.