This paper deals with the Autler-Townes doublet structure. Applied driving and probing laser fields can have arbitrary intensities. An explanation is given of the broadening of doublet components with the growth of probing field intensity, which was observed in experiment. The effects of Doppler averaging are discussed.
Some features of the optical Autler-Townes effect as observed in Doppler-broadened three-level systems, including the physical significance of the observed line splitting, the conditions for the observation of the doublet, the doublet separation and the detuning effects, are discussed in this paper. A graphical illustration of the phenomenon, based on a search for on-resonance velocity groups, is proposed which allows a complete qualitative discussion of the effect and shows that the observed doublet is not really a splitting of the resonance as for the atom at rest but rather corresponds to a frequency hole where the laser probe does not see any resonant velocity group. The method is applied to real three-level systems of neon as typical cases. A semi-classical density-matrix calculation is performed numerically and definitely confirms the results of the qualitative graphical discussion ; furthermore it shows that, for many experimental situations, the first order approximation is inadequate. The observation of the Autler-Townes doublet in a new experiment using two dye lasers is reported. The experimental results and that of one of our previous experiments are compared with the theoretical predictions ; the agreement is quite satisfactory.
With a coupling laser locked to caesium 6S 1/2 F g =4–6P 3/2 F e =5 cycling transition and a co-propagating probe laser scanned across 6S 1/2 F g =4–6P 3/2 F e =3, 4 and 5 transitions, a novel scheme for sub-Doppler spectra in Doppler-broadened V-type three-level system is demonstrated by detecting the transmission of the coupling laser through a caesium vapour cell. The Autler–Townes doublet in the sub-Doppler spectra of the coupling laser is clearly observed. The effects of coupling laser intensity on the splitting and linewidth of the Autler–Townes doublet are experimentally investigated and the results agree well with theoretical predictions. Taking the multiple hyperfine levels of caesium atom into account, a brief analysis is presented.
Theoretical analysis of the Autler-Townes splitting pattern in a three-level cascade excitation of a Doppler-broadened sample reveals that the observed Autler-Townes splitting is not only a function of the coupling-laser Rabi frequency, as in the homogeneously broadened case, but can also strongly depend on the wavenumber ratio of the coupling and probe lasers. Utilizing a steady-state density matrix formalism, we derive exact expressions for the populations of the intermediate and upper levels for a homogeneously broadened system. In the limit of a weak probe field, analytical expressions for Doppler-broadened excitation spectra from the intermediate and upper levels are derived. Using these expressions, we investigate the critical role of Doppler broadening on the observation of Autler-Townes splitting and its asymptotic behavior as a function of the coupling Rabi frequency for counterpropagating and copropagating configurations for different wavenumber ratios of the lasers.
We have experimentally studied the reflection of a weak probe beam from a dense atomic potassium vapor in the presence of a strong laser field tuned to the atomic resonance transition. We have observed an Autler-Townes doublet under hitherto unexplored conditions, namely, that the Rabi frequency induced by the strong laser field is much smaller than the self-broadened width of the resonance transition of the unexcited vapor. We attribute our observation to a reduction of the atomic decoherence by the strong drive field. We present a theoretical model of nonlinear processes in a dense atomic gas to explain the observed results.