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Journal of Contemporary Physics (Armenian Academy of Sciences)

Investigations of Atomic Transitions of the D2 Line of Potassium in Strong Magnetic Fields Using Saturated Absorption Technique in a Microcell

Armen D. Sargsyan

Published Mar 1, 2023• 1 citation
Publisher

Abstract

Abstract Atomic transitions of 39K, D2 line are studied in strong longitudinal magnetic fields, up to 1000 G, with a high spectral resolution. The saturated absorption (SA) method was used in a micro-cell filled with K vapors with a thickness of L= 30 µm. A double differentiation of the SA spectrum was carried out, which made it possible to obtain narrow (~50 MHz) atomic lines and study individual transition frequency and probabilistic behavior. Among alkali metals, the K atoms have the smallest hyperfine splitting of the ground levels. This allows one to observe the break of the coupling between the electronic total angular momentum J and nuclear I angular momentums at relatively low magnetic fields B > 300 G. In the case of using circularly polarized radiation (σ+ or σ–), two groups (each consisting of four) equidistantly located total eight atomic transitions are recorded in strong magnetic fields. The experimental results are well described by a known theoretical model.

DOI
10.1134/s1068337223010176

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arXiv:2203.11553•Applied Optics•Jun 17, 2022•14 citations
Abstract Atomic transitions of 39K, D2 line are studied in strong longitudinal magnetic fields, up to 1000 G, with a high spectral resolution. The saturated absorption (SA) method was used in a micro-cell filled with K vapors with a thickness of L= 30 µm. A double differentiation of the SA spectrum was carried out, which made it possible to obtain narrow (~50 MHz) atomic lines and study individual transition frequency and probabilistic behavior. Among alkali metals, the K atoms have the smallest hyperfine splitting of the ground levels. This allows one to observe the break of the coupling between the electronic total angular momentum J and nuclear I angular momentums at relatively low magnetic fields B > 300 G. In the case of using circularly polarized radiation (σ+ or σ–), two groups (each consisting of four) equidistantly located total eight atomic transitions are recorded in strong magnetic fields. The experimental results are well described by a known theoretical model.
Atomic transitions of the 39 K potassium isotope in strong (up to 1 kG) longitudinal and transverse magnetic fields have been studied with a high spectral resolution. It has been shown that crossover resonances are almost absent in the saturated absorption spectrum of potassium vapors in a 30-μm-thick microcell. This, together with the small spectral width of atomic transitions (~30 MHz), allows one to use the saturated absorption spectrum for determining frequencies and probabilities of individual transitions. Among the alkali metals, potassium atoms have the smallest magnitude of the hyperfine splitting of the lower level. This allows one to observe the break of the coupling between the electronic and nuclear angular momentums at comparatively low magnetic fields B > 500 G, i.e., to implement the hyperfine Paschen–Back regime (HPB). In the HPB regime, four equidistantly positioned transitions with the same amplitude are detected in circularly polarized light (σ + ). In linearly polarized light (π) at the transverse orientation of the magnetic field, the spectrum consists of eight lines which are grouped in two groups each of which consists of four lines. Each group has a special distinguished G-transition and the transition that is forbidden in the zero magnetic field. In the HPB regime, the probabilities of transitions in a group and derivatives of their frequency shifts with respect to the magnetic field asymptotically tend to magnitudes that are typical for the aforesaid distinguished G-transition. Some practical applications for the used microcell are mentioned.
Abstract It is demonstrated that the use of a micrometric thin 39 K vapor cell (MTC) and saturated absorption (SA) spectroscopy allows the formation of narrow atomic lines in the transmission spectrum without unwanted cross-over resonances. Another important feature is the small characteristic magnetic field value B 0 = A h f / μ B of 39 K, significantly smaller than for Rb and Cs. As a consequence, decoupling of J and I can be observed at relatively low magnetic fields ∼300 G, which results in the formation of two groups of four spectrally-resolved and equidistantly-positioned atomic transitions having the same amplitude (each group corresponds to a given circular polarization σ ± ) which we record using a simple experimental setup with a linearly polarized tunable diode-laser and a longitudinal magnetic field obtained with two permanent magnets. Fabrication of a MTC is much easier than the fabrication of the 39 K nanocells used in our previous works. A simple method to determine the magnitude of a wide range of B -fields with a spatial resolution of 30 µ m is presented, which is intrinsically calibrated and does not require a frequency reference.
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.
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.
Abstract In strong magnetic fields (0.1–6 kG), many atomic lines closely spaced in frequency appear in the absorption spectrum of alkali metal vapors. Due to the small frequency interval between them and the Doppler broadening of the atomic lines, they are overlapped. For spectral separation and study of individual atomic lines, it is necessary to ensure their spectral narrowing. It is shown that this can be done using the saturated absorption method in an atomic vapor contained in a 30 μm-thick cell filled with Rb vapor. All 10 atomic transitions of Rb D1 line are spectrally very well resolved in the second derivative of the saturated absorption spectrum. Complete resolution of atomic transitions makes this method useful for the determination of a wide range of magnetic fields. The theoretical curves describe the experimental results very well.
39 K atoms have the smallest ground state ( 2 S 1 / 2 ) hyperfine splitting of all the most naturally abundant alkali isotopes and, consequently, the smallest characteristic magnetic field value B 0 = A 2 S 1 / 2 / μ B ≈ 170 G , where A 2 S 1 / 2 is the ground state’s magnetic dipole interaction constant. In the hyperfine Paschen–Back regime ( B ≫ B 0 , where B is the magnitude of the external magnetic field applied on the atoms), only eight Zeeman transitions are visible in the absorption spectrum of the D 1 line of 39 K , while the probabilities of the remaining 16 Zeeman transitions tend to zero. In the case of 39 K , this behavior is reached already at relatively low magnetic field B > B 0 . For each circular polarization ( σ − , σ + ), four spectrally resolved atomic transitions having sub-Doppler widths are recorded using a sub-microsized vapor cell of thickness L = 120 − 390 n m . We present a method that allows to measure the magnetic field in the range of 0.1 − 10 k G with micrometer spatial resolution, which is relevant in particular for the determination of magnetic fields with large gradients (up to 3 G/µm). The theoretical model describes well the experimental results.