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Journal of Contemporary Physics (Armenian Academy of Sciences)

Modified Faraday Rotation Method for Studying Cesium Atomic Lines in Strong Magnetic Fields

Armen D. Sargsyan, A. Tonoyan, G. Hakhumyan, A. Amiryan, P. Todorov, S. Cartaleva, David G. Sarkisyan

Published Jan 1, 2019• 1 citation
Publisher

Abstract

A modified Faraday rotation method is developed using a nanocell filled with cesium vapor. Formed atomic lines have a spectral width 1.5–2 times narrower than those obtained by the Faraday rotation method. In magnetic fields of B = 5000–7000 G, all the atomic transitions of the Cs D 2 lines, formed in the spectra, are spectrally resolved and identified. In particular, transitions that are forbidden at B = 0 G have been investigated, however, at certain values of the magnetic field, there is a gigantic increase in their probabilities. It is shown that the modified Faraday rotation method is convenient and efficient for high-resolution spectroscopy for Cs atoms. There is а good agreement between the experimental results and calculated values. The practical applications are also noted.

DOI
10.3103/s1068337219010110

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Journal of Contemporary Physics (Armenian Academy of Sciences)•Jul 1, 2018•1 citation
A modified Faraday rotation method is developed using a nanocell filled with cesium vapor. Formed atomic lines have a spectral width 1.5–2 times narrower than those obtained by the Faraday rotation method. In magnetic fields of B = 5000–7000 G, all the atomic transitions of the Cs D 2 lines, formed in the spectra, are spectrally resolved and identified. In particular, transitions that are forbidden at B = 0 G have been investigated, however, at certain values of the magnetic field, there is a gigantic increase in their probabilities. It is shown that the modified Faraday rotation method is convenient and efficient for high-resolution spectroscopy for Cs atoms. There is а good agreement between the experimental results and calculated values. The practical applications are also noted.
Abstract A nanocell filled with atomic vapors of rubidium and potassium was used to develop a modified method of Faraday rotation. The formed lines are characterized by a spectral width that is a factor of 1.5‒2 smaller than those obtained by traditional method of Faraday rotation in nanocells. The new method allows obtaining the spectral width of atomic line that is 8 times smaller than the Doppler broadening in the case of the D2 line of rubidium and 15 time smaller than the Doppler broadening in the case of the D1,2 lines of potassium. In magnetic fields B = 100−1200 G, all atomic lines of Rb and K atoms are spectrally resolved and identified. In the case of the D2 line of Rb, it is demonstrated that the probabilities of magneto-induced transitions (87Rb, Fg = 1 → Fe = 3 and 85Rb, Fg = 2 → Fe = 4) can exceed the probabilities of the allowed transitions. Convenience and efficiency of the modified method of Faraday rotation for high-resolution spectroscopy is demonstrated.
We show that the Faraday rotation (FR) in strong longitudinal magnetic fields is a convenient tool to study atomic transitions by using the D1 line in a Cs vapour confined in a nanocell of thickness L≈450 nm. We use strong magnetic fields ranging from 0.1 to 6 kG, in which Cs atomic transitions are split into a large number of components, and FR signals of spectral width of ∼ 50 MHz are frequency-resolved allowing the investigation of individual transitions. For magnetic fields of several kG, the hyperfine Paschen–Back regime is reached that is manifested by the presence in the spectrum of the eight FR components having the amplitudes of the same height and located with almost equidistant frequencies. A remarkable feature of FR spectrum is the proportionality of its amplitude to the probability of an atomic transition in a strong magnetic field. A theoretical model which agrees well with the experiment is developed.
AbstractA nanocell filled with atomic vapors of rubidium and potassium was used to develop a modified method of Faraday rotation. The formed lines are characterized by a spectral width that is a factor of 1.5‒2 smaller than those obtained by traditional method of Faraday rotation in nanocells. The new method allows obtaining the spectral width of atomic line that is 8 times smaller than the Doppler broadening in the case of the D _2 line of rubidium and 15 time smaller than the Doppler broadening in the case of the D _1,2 lines of potassium. In magnetic fields B = 100−1200 G, all atomic lines of Rb and K atoms are spectrally resolved and identified. In the case of the D _2 line of Rb, it is demonstrated that the probabilities of magneto-induced transitions (^87Rb, F _ g = 1 → F _ e = 3 and ^85Rb, F _ g = 2 → F _ e = 4) can exceed the probabilities of the allowed transitions. Convenience and efficiency of the modified method of Faraday rotation for high-resolution spectroscopy is demonstrated.
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.
Features of the effect of Faraday rotation (the rotation of the radiation polarization plane) in a magnetic field of the D 1 line in Cs atomic vapor in a nanocell with the thickness L varying in the range of 80–900 nm have been analyzed. The key parameter is the ratio L/λ, where λ = 895 nm is the wavelength of laser radiation resonant with the D 1 line. The comparison of the parameters for two selected thicknesses L = λ and λ/2 has revealed an unusual behavior of the Faraday rotation signal: the spectrum of the Faraday rotation signal at L = λ/2 = 448 nm is several times narrower than the spectrum of the signal at L = λ, whereas its amplitude is larger by a factor of about 3. These differences become more dramatic with an increase in the power of the laser: the amplitude of the Faraday rotation signal at L = λ/2 increases, whereas the amplitude of the signal at L = λ almost vanishes. Such dependences on L are absent in centimeter-length cells. They are inherent only in nanocells. In spite of a small thickness, L = 448 nm, the Faraday rotation signal is certainly detected at magnetic fields ≥0.4 G, which ensures its application. At thicknesses L < 150 nm, the Faraday rotation signal exhibits “redshift,” which is manifestation of the van der Waals effect. The developed theoretical model describes the experiment well.
Theoretical studies of the Faraday rotation (FR) effect in alkali vapors contained in extremely thin cells are presented. It is shown that the spectra of the FR signal are well frequency resolved despite the huge number of atomic transitions. This allows one to study the evolution of the Cs D 1 (λ = 895 nm) line hyperfine structure of F g = 4 → F e = 3, 4 atomic transitions in magnetic fields. The presented theoretical model predicts the coherent Dicke narrowing effect and its revival with a periodicity Δ L = λ. The practical applications of the FR are noted.