Decoupling of hyperfine structure of Cs D_1 line in strong magnetic field studied by selective reflection from a nanocell

Abstract

Decoupling of total electronic and nuclear spin moments of Cs atoms in external magnetic field for the case of atomic D 1 line, leading to onset of the hyperfine Paschen-Back regime has been studied theoretically and experimentally. Selective reflection of laser radiation from an interface of dielectric window and atomic vapor confined in a nanocell with 300 nm gap thickness was implemented for the experimental studies. The real time derivative of selective reflection signal with a frequency position coinciding with atomic transitions was used in measurements, providing ∼ 40 MHz spectral resolution and linearity of signal response in respect to transition probability. Behavior of 28 individual Zeeman transitions in a wide range of longitudinal magnetic field (0 -6 kG) has been tracked under excitation of Cs vapor by a low-intensity σ + -polarized cw laser radiation. For B ≥ 6 kG, only 8 transitions with nearly equal probabilities and the same frequency slope remained in the spectrum, which is a manifestation of the hyperfine Paschen-Back regime. The obtained experimental results are consistent with numerical modeling. Due to small divergence of selective reflection signal, as well as sub-wavelength thickness and sub-Doppler spectral linewidth inherent to nanocell, the employed technique can be used for distant remote sensing of magnetic field with high spatial and B-field resolution. I IntroductionOptical nanometric thin cell (nanocell) containing atomic vapor of alkali metal (Rb, Cs, K, Na) is proven to be efficient and convenient spectroscopic tool for magneto-optical studies of optical atomic transitions between the hyperfine levels in strong external magnetic fields. Two interconnected effects develop with the increase of Bfield: strong deviation of Zeeman splitting of hyperfine transitions from linear dependence, and significant change in probability of individual Zeeman transitions [1,2,3]. The efficiency of nanocell technique for quantitative spectroscopy of the Rb atomic transitions in strong magnetic field (up to 7 kG) resulting in onset of the hyperfine Paschen-Back regime was demonstrated in [4,5,6]. The presence of specific "guiding" transitions foretelling characteristics of all other transitions between magnetic sublevels of alkali atoms D 1 line excited by π-polarized radiation in a strong transversal magnetic field was recently shown in [7]. Micro-and nanocells were used in [8] to study the onset of hyperfine Paschen-Back regime for Cs D 2 line in magnetic fields up to 9 kG. Realization of 1 arXiv:1610.09807v1 [physics.atom-ph]

Dark resonance formation with magnetically induced transitions: extension of spectral range and giant circular dichroism

“…In recent years, there was a noticeable interest to F e − F g = ∆F = ±2 atomic transitions between the lower (F g ) and upper (F e ) levels of the hyperfine structure of alkali metals (Cs, Rb, K, Na), where F is the total atomic momentum. According to the selection rules, these transitions are forbidden in a zero magnetic field, however, in a magnetic field of ∼ 1000 G, their probabilities undergo giant increase (so called magnetically induced (MI) transitions) [8][9][10][11][12]. It was demonstrated that the probabilities of MI transitions (their overall number for atoms of alkali metals is more than 70) can significantly exceed the probabilities of "allowed" atomic transitions in the range of B = 300−1000 G. Also, the following rule has been found: the intensities of MI transitions with ∆F = +2(−2) are maximal in the case of σ + (σ − ) polarized excitation [8][9][10][11][12].…”

“…It is easy to see that the sign of C MCD indicates prevailing contribution to the achieved DR intensity (the sign is positive for σ + and negative for σ − coupling). Figure 6 shows the B-field dependence of C MCD coefficient calculated using the theoretical model described in [8][9][10]. The calculations were done for two cases.…”

Selective reflection from an Rb layer with a thickness below λ/12 and applications

“…The B-field strength was varied by simple longitudinal displacement of the magnet. ing in the derivative of the SR signal are presented in [11,12]. The DSR peaks labeled 1-3 and 10 belong to 87 Rb, and the DSR peaks 4-9 belong to 85 Rb (see the upper diagrams).…”

The theory of selective reflection for a Fabry–Perot interferometer

“…Therefore, here, like in (5), there are no problems with infinities. If we set n 1 = n 2 = n 0 in the expression for R from (19) we can obtain a more simpler expression for the reflection…”