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Optics and Spectroscopy

Studying the regime of complete decoupling of the bond between the electron and nuclear moments at the D 1-line of the 39K potassium isotope using a spectroscopic microcell

Armen D. Sargsyan, A. Amiryan, T. A. Vartanyan, David G. Sarkisyan

Published Dec 1, 2016• 8 citations
Publisher

Abstract

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.

DOI
10.1134/s0030400x16120213

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arXiv:1707.04468•Jul 14, 2017•0 citations
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 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.
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.
Decoupling of total electronic and nuclear spin moments of Cs atoms in an external magnetic field for the case of atomic D1 line, leading to onset of the hyperfine Paschen–Back (HPB) regime, is studied theoretically and experimentally. Selective reflection (SR) of laser radiation from an interface of dielectric window and atomic vapor confined in a nanocell with 300 nm gap thickness is implemented for the experimental studies. The real-time derivative of SR signal with a frequency position coinciding with atomic transitions is used in the measurements, providing ∼40 MHz spectral resolution and linearity of the signal response with respect to the transition probability. The behavior of 28 individual Zeeman transitions in a wide range of longitudinal magnetic field (0–6 kG) is tracked under the excitation of Cs vapor by a low-intensity σ+-polarized cw laser radiation. For B≥6 kG, only eight transitions with nearly equal probabilities and the same frequency slope remain in the spectrum, which is a manifestation of the HPB regime. The obtained experimental results are in very good agreement with the numerical modeling. A small divergence of the SR signal as well as subwavelength thickness and sub-Doppler spectral linewidth inherent to nanocell make it possible for the employed technique to be used for distant remote sensing of a magnetic field with high spatial and B-field resolution.
A one-dimensional nano-metric-thin cell (NC) filled with potassium metal has been built and used to study optical atomic transitions in external magnetic fields. These studies benefit from the remarkable features of the NC allowing one to use and λ methods for effective investigations of individual transitions of the K D 1 line. The methods are based on strong narrowing of the absorption spectrum of the atomic column of thickness L equal to and to λ (with being the resonant laser radiation wavelength). In particular, for a π -polarized radiation excitation the λ -method allows us to resolve eight atomic transitions (in two groups of four atomic transitions) and to reveal two remarkable transitions that we call guiding transitions (GT). The probabilities of all other transitions inside the group (as well as the frequency slope vs . magnetic field) tend to the probability and to the slope of GT. Note that for circular polarization there is one group of four transitions and GT do not exist. Among eight transitions there are also two transitions (forbidden for ) with the probabilities undergoing strong modification under the influence of magnetic fields. Practically the complete hyperfine Paschen-Back regime is observed at relatively low magnetic fields. Note that for the K D 2 line GT are absent. Theoretical models describe the experiment very well.
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.
Theoretical Investigation of 41^{41}41K States Behavior under Strong Magnetic Field and πππ Polarized Laser Field
Theoretically research of the behavior of 41^{41}41K D1D_1D1​ and D2D_2D2​ lines for πππ polarized resonant light is conducted in the presence of strong magnetic field when the total electronic angular momentum JJJ and nuclear spin III are decoupled. We show that in the case of linear polarization and for D1 line there are two transitions, so called guiding transitions (GT) that maintain their probabilities and frequency slopes. In Hyperfine Paschen-Back (HPB) regime other transitions are coming together to those GTs, making 2 groups (4 in each). Each transition in the group has the same frequency slope and probability as the GT in their group. It is demonstrated that from 12 (D1D_1D1​) and 20 (D2D_2D2​) initially allowed Zeeman transitions (taking into account the selection rules) at low B-field, only 8 transitions in each DDD line remain in absorption spectra at B>200B > 200B>200 G. A complete HPB regime for relatively low magnetic fields B∼200B \sim 200B∼200 G has been observed. This value is the smallest for all alkali metals.