Magnetically Induced Transitions in Spectral Vicinity of the D2 Line of Cs Atoms: Giant Growth of Transition Probabilities and Different Asymptotic Behavior in Increasing Transverse Magnetic Field
Armen D. Sargsyan, A. Tonoyan, T. A. Vartanyan, David G. Sarkisyan
Abstract Two types of magnetically induced (MI) transitions in cesium atoms were studied experimentally and theoretically. The MI transitions are forbidden in the absence of magnetic field. Probabilities of MI transitions rapidly grow with increase in magnetic field and can exceed those of transitions allowed in the absence of magnetic field. Asymptotic behavior of probabilities of MI transitions in strong magnetic fields is different. In the case of magnetically induced transitions of the first type (MI1), transition probabilities experience giant increase with increase in the applied magnetic field, and with a further increase of the magnetic field, the probabilities of these transitions tend to asymptotic large value. Probabilities of magnetically induced transitions of the second type (MI2) also experience giant increase with increase in the applied magnetic field. However, probabilities of such transitions tend to zero again with further increase in the magnetic field. It is demonstrated that measurement of the second derivative (SD) of absorption spectra of Cs vapor contained in a nanocell with thickness L = 426 nm corresponding to half the wavelength of the D2 line of cesium (λ = 852 nm) enables conducting Doppler-free spectroscopy. Narrow width of atomic lines and linear relation between the SD signal amplitudes and transition probabilities allows studying individual atomic transitions in an external transverse magnetic field with induction varying from 0.5 to 5.3 kG. In particular, four MI transitions were studied: two MI1 and two MI2 ones. Theoretical calculations agree well with the experimental results.
Abstract Two types of magnetically induced (MI) transitions in cesium atoms were studied experimentally and theoretically. The MI transitions are forbidden in the absence of magnetic field. Probabilities of MI transitions rapidly grow with increase in magnetic field and can exceed those of transitions allowed in the absence of magnetic field. Asymptotic behavior of probabilities of MI transitions in strong magnetic fields is different. In the case of magnetically induced transitions of the first type (MI1), transition probabilities experience giant increase with increase in the applied magnetic field, and with a further increase of the magnetic field, the probabilities of these transitions tend to asymptotic large value. Probabilities of magnetically induced transitions of the second type (MI2) also experience giant increase with increase in the applied magnetic field. However, probabilities of such transitions tend to zero again with further increase in the magnetic field. It is demonstrated that measurement of the second derivative (SD) of absorption spectra of Cs vapor contained in a nanocell with thickness L = 426 nm corresponding to half the wavelength of the D2 line of cesium (λ = 852 nm) enables conducting Doppler-free spectroscopy. Narrow width of atomic lines and linear relation between the SD signal amplitudes and transition probabilities allows studying individual atomic transitions in an external transverse magnetic field with induction varying from 0.5 to 5.3 kG. In particular, four MI transitions were studied: two MI1 and two MI2 ones. Theoretical calculations agree well with the experimental results.
Two types of magnetically induced transitions (MI transitions) in cesium atoms have been studied experimentally and theoretically. In the absence of a magnetic field MI, transitions are forbidden. As the magnetic field increases, the probabilities of MI transitions grow rapidly and can exceed the probabilities of transitions allowed in the absence of a magnetic field. The asymptotic behavior of the probabilities of MI transitions in strong magnetic fields is different. In the case of magnetically-induced transitions of the first type (MI1), with an increase in the applied magnetic field, the probability of these transitions increases enormously, and with a further increase in the magnetic field, the probabilities of these transitions tend to a constant value. In the case of magnetically induced transitions of the second type (MI2), with an increase in the applied magnetic field, there is also a giant increase in the probability of these transitions; however, with a further increase in the field, the probabilities of these transitions again tend to zero. It is shown that measuring the second derivative (SD) of the absorption spectra of Cs vapors enclosed in a nanocell with a thickness of L = 426 nm, corresponding to half the wavelength of the D2 line of cesium λ = 852 nm, allows one to perform Doppler-free spectroscopy. The small width of atomic lines and the linearity of the SD signal response in accordance with the transition probabilities make it possible to study individual atomic transitions in an external transverse magnetic field with an inductance of 0.5 to 5.3 kG. In particular, four MI transitions were investigated: two MI1 and two MI2. The theoretical calculations are in good agreement with the experimental results
Abstract In this paper we show that the second derivative (SD) technique of the absorption spectra of Rb atomic vapours, confined in a nanocell with a thickness ℓ = λ /2 = 398 nm, allows us to achieve close to Doppler-free spectroscopy. The narrow linewidth and linearity of the SD signal response with respect to transition probabilities allows us to study separately, in an external transverse magnetic field (0.6 to 4 kG), a large number of the atomic transitions of 85 Rb and 87 Rb atoms. Atomic transitions | F g , 0⟩ → | F e = F g , 0′⟩, for which the dipole moment is null in a zero magnetic field (so-called magnetically-induced transitions), show a gigantic increase in probability with an increasing magnetic field. When a magnetic field is applied to the vapour, we show the possibility of forming a dark resonance on these transitions by adding a coupling laser. We are therefore able to demonstrate a five-fold increase in the transmission of the probe radiation when the coupling laser is on. Theoretical calculations are in very good agreement with the experimental results.
Atomic transitions of D 2 line of Cs atoms in strong transverse magnetic fields up to 7 kG with the high spectral resolution were studied for the first time. The λ/2 method based on the nanocell with the half-wavelength thickness L = λ/2 = 426 nm is used, which allows one to trace the behavior of each of the individual atomic transitions. When the laser radiation has the linear π polarization and magnetic fields B is more than 5 kG, only 16 atomic transitions, which have almost the same amplitudes, remain in the absorption spectrum (at lower fields there are 56 transitions). There is a good agreement between the experiment and the theory.
Atomic transitions in alkali metals that have zero probability in the absence of a magnetic field but have large probabilities in the presence of a magnetic field are called magnetically induced (MI). They are of interest because of their large probabilities, which exceed the probabilities of usual transitions in a wide magnetic field range. Magnetically induced transitions are classified as type-1 (MI1) and type-2 (MI2) and their total number is about 100. In this work, MI2 transitions are examined between ground Fg and excited levels Fe of the hyperfine structure satisfying the condition Fe−Fg=ΔF=±2 , which are forbidden in zero magnetic field but have large probabilities in the presence of a magnetic field. The probabilities of the MI2 transitions with ΔF=+2 and the MI transitions with ΔF=−2 are maximal in the case of optical radiation with the σ+ and σ– polarizations, respectively. This difference is called type-1 magnetically induced circular dichroism (MICD1). It has been shown for the first time that the probability of the strongest MI2 transition in the 85Rb atom corresponding to the D2 line in magnetic fields >100 G in the case of σ+ radiation is larger than the probability of the strongest MI2 transition in the case of σ– radiation by a factor of 2.5. This difference is called type-2 magnetically induced circular dichroism (MICD2). It has been shown how to determine the strongest MI transition for any alkali metal atom, which is important for its application in magneto-optical processes. Theoretical curves reproduce well experimental results.
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.
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.