Level-crossing absorption with narrow spectral width in Rb vapor with buffer gas

Abstract

We present the transformation in the Hanle configuration of the transmission that results from coherent population trapping (CPT) into the level-crossing absorption (LCA) that results from the single-photon optical pumping in the 87 Rb D 1 line of a Rb vapor cell with a Ne buffer gas when the polarization of the laser field is changed from linear to circular. The LCA spectrum, with a narrow spectral width of 2.4 mG (1.7 kHz), was observed in the F g → F e F g transition with the circularly polarized laser. This may be because the LCA is both related to the transverse magnetic field and the atom-laser interaction time resulting from diffusive atomic motion in the cell with the buffer gas. The CPT and LCA spectra were calculated numerically using the full density matrix equations for the relevant magnetic sublevels of the hyperfine levels, considering the residual magnetic fields perpendicular to laser propagation and the collision effects resulting from the buffer gas. There was good qualitative agreement between theoretical and experimental results.

Calculated Hanle transmission and absorption spectra of theRb87D1line with residual magnetic field

“…A comparison with the experimental results presented in Ref. [37] showed that the magnitude of the transverse magnetic field was approximately 1 mG.…”

“…Therefore, information obtained at the condition of the elliptic polarization may be used to determine the angle between the x axis and the direction of the transverse magnetic field. Figure 6(b) shows the experimental results presented in a previous report [37]. A rough comparison of Figs.…”

“…Based on the experimental observation achieved in a previous report [37], this paper reports the results of a detailed theoretical study on the transmission and absorption spectra in the Hanle configuration. The paper is organized as follows.…”

“…They explained this phenomenon using a transverse magnetic field which redistributes the population of the magnetic sublevels, resulting in absorption. Quite recently, Yu et al observed * hrnoh@chonnam.ac.kr † hsmoon@pusan.ac.kr subnatural level-crossing absorption and transmission signals using a circularly and linearly polarized beam, respectively, for a Rb cell with a buffer gas [37].…”

Beyond Quantum interference and Optical pumping: invoking a Closed-loop phase

“…We further note that for finite B-field the role of QI is negligible and OP drives the direction dependent absorption. Even in absence of QI such direction dependent OP response has been associated with EIT or EIA [30][31][32].…”