Autler-Townes splitting

Figure 9.7 A ground state j) is excited by a weak laser pulse e, to a resonance state q) belonging to a space Q decaying radiatively or nonradiatively to a space P. The q) state is coupled optically to a third state ) by strong guiding field 2 and undergoes as a result Autler-Townes splitting. As a...

Apparently, the time evolution of the IEq) component of 2i(t)) is governed by a quasi-energy of Eq - Q2(0I> whereas the time evolution of the I q) component of U2(0) is governed by a quasi-energy of + f22(0l- hi such a case, one says that the two levels are Autler-Towns split by an amount equal to 2 i22(0l ... 

The result is shown as the dot-dash curve of Figure 9.11. It is shown that the spontaneous emission has been effectively suppressed, with the suppression becoming more effective, the smaller is the Autler-Townes splitting A due to the CW laser. Also shown in Figure 9.11 (as the dashed line) are the natural decay curves, arising when we start with one of the eigenstates. As can be seen, this decay, which is nonexponential due to the interaction between the resonances, is still much faster than the suppressed decay aided by the interruptions. 

Figure 9.11 Suppression of the 2P-1S spontaneous emission in the hydrogen atom, for which the natural linewidth is 1.66 X 10 cm". The solid lines display the decay of the optimized superposition of the Autler-Townes split levels with no interruptions. The dot-dashed lines are the decay curves of the same superposition states in the presence of interruptions. The dashed lines display the average decay of the two Autler-Townes split components. The optimization time t (marked by a triangle) is 0.2/T(= 0.65 ns), and the total time range displayed is up to 3/r(= 10 ns). A is the Autler-Townes splitting induced by the CW laser and T denotes the natural linewidth. Reprinted figure by permission from Ref. [38]. Copyright 2003 by the American Physical Society.

In Figure 9.7 we illustrate the formation of the analogous EIT dark state, as described by Eq. (9.59), as a function of time. We see that when the pulse is weak (t = 1.7) the (Autler-Townes) splitting between the two field-dressed states is small and the EIT dark state resembles a very narrow hole. As the pulse gets... 

Fig. 9.7 Formation of the EIT hole as a result of an Autler-Townes splitting of a resonance according to Eq. (9.59). Shown is the line shape at three different times, at the peak of the pulse t — 0, as the pulse begins to wane, t = 0.85, and at the tail of the pulse, t = 1.7. A simple Gaussian pulse of the form 2(0 = n exp(—t2) was assumed.

Although all the examples chosen involve singlet states, for which the theory is especially simple, there is no problem in extending the method to more complex Zeeman patterns, or indeed in including the effect of Paschen-Back uncoupling on the MOV spectrum [166]. The influence of -mixing on MOV patterns has also been studied, and is in principle well understood [167], If the experiment is performed with lasers, the influence of laser power on Faraday rotation arises both by population transfer and by the Autler-Townes splitting (section 9.10) [173]. 

Fig. 7.13 Two-evanescent-wave fluorescence spectra of sodium atoms excited near the critical angles. Each line exhibits Autler-Townes splitting. Reprinted with permission from Bordo and Rubahn (1999a). Copyright 1999, Opticai Society of America.

Fig. 7.14 (a) Dependence of the measured Autler-Townes splitting on the prism temperature for fixed EW intensity, (b) Fit to the experimental data, resulting in the EW amplitude... 

Field splitting of energy levels (see Fig. 2.8) can also be observed in transitions from level 1 or 2 to some third level. As a result, of this sphtting, the spectral line of the 2 —> 3 transition is split into two hnes (Fig. 2.8(b)). This phenomenon was first observed in microwave spectroscopy (the Autler-Townes effect (Autler and Townes 1955)). In the optical region of the spectrum and in the presence of phase relaxation, such a splitting can apparently be observed only if condition (2.62) is satisfied, that is, when the response of the two-level system to the laser-light field is truly oscillatory. 

---