The Autler—Townes effect is considered for the case where a strong control field acts in the frequency profile of a hyperfine transition taking into account the hyperfine interaction. An exact expression is derived for the susceptibility of the medium with respect to a probe field that acts in the frequency profile of a coupled transition of the alkaliatom D 1 line. It is shown that the hyperfine interaction in the excited state may substantially modify the susceptibility of the medium. In particular, it is shown that, when the control field is tuned to wings of atomic transitions, the structure of the Autler—Townes resonances appears to be noticeably differing from what is predicted by the Λ-scheme approximation. It is found that tuning of the control field frequency to between hyperfine components of the excited state enhances the resonant structure in this region. The results are discussed in terms of the quantum memory protocols based on the effects of Raman scattering and electromagnetically induced transparency.
Sodium vapor, in the density range
1013 to 5 \ifmmode\times\else\texttimes\fi{}
1014 ${\mathrm{cm}}^{\ensuremath{-}3}$, was excited by a cw dye laser, tuned 20-150 GHz from either the
D1 or
D2 resonance line. We observed a three-peak scattered spectrum, consisting of the Rayleigh component at the laser frequency, and the two fluorescence components (direct and sensitized) at the atomic resonance-line frequencies. Corrections to the Rayleigh signals for anisotropy and polarization effects, and to the fluorescence signals for radiation trapping, were made in order to obtain the ratio of the sum of the total intensities of the two fluorescence components to that of the Rayleigh component. This ratio combined with a measurement of the line-wing absorption coefficient yields the sodium density and the
D-line self-broadening rate coefficients [${k}_{\mathrm{br}}=4.67\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$
cm3${\mathrm{s}}^{\ensuremath{-}1}$ (\ifmmode\pm\else\textpm\fi{}15%) for the
D2 line and ${k}_{\mathrm{br}}=3.07\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$
cm3${\mathrm{s}}^{\ensuremath{-}1}$ (\ifmmode\pm\else\textpm\fi{}15%) for the
D1 line]. Asymmetry in the self-broadened line wings due to fine-structure recoupling was observed. The measured intensity ratio of the
D lines, combined with pulsed measurements of the effective radiative decay rates in the presence of radiation trapping, yields the fine-structure collisional-mixing cross section [$\ensuremath{\sigma}(3{P}_{\frac{3}{2}}\ensuremath{\rightarrow}3{P}_{\frac{1}{2}})=172$
A˚2(\ifmmode\pm\else\textpm\fi{}18%)] at $T\ensuremath{\cong}300\ifmmode^\circ\else\textdegree\fi{}$ C. Our results are compared to other experiments and to theory.
The linewidth in level-crossing experiments as normally carried out is the sum of the natural widths of the levels concerned. We have reduced the linewidth by taking the fluorescent light, not from all atoms in the assembly, but from a sample biased in favour of those which have survived as excited atoms for times longer than the average. This was achieved by pulse techniques. Improved resolution was obtained of the components on the wing of the zero-field level-crossing curve for the level 3 2P3/2 in 23Na. The values obtained for the hyperfine-coupling constants are a = 185 ± 040 MHz, b = 30 ± 06 MHz, in agreement with values found in double-resonance experiments. The present values do not represent the limit of the method, since the experiment was designed to investigate the technique, not to make precision measurements. A theoretical analysis of the method reveals that level-crossing curves obtained by this technique may, in certain circumstances, have undesirable satellites. It is shown how the line profile may be controlled and improved without too great a sacrifice in statistical accuracy.