In a double resonance experiment with a strong pump beam and a weak probe beam multiplet structures due to the AC Stark effect can be observed. The authors report the first observation of such a multiplet in a three-level experiment. The linearly polarised beams from a CW dye laser and a I 2 stabilised He-Ne laser were counter-propagating in the neon discharge cell and the saturating laser frequency was tuned across the resonances. The quadruplet structure was observed both for zero and for non-zero detuning delta 2 of the probe beam. The corresponding calculations for the three-level system with degenerate levels have been performed using the density matrix formalism with a tensorial expansion of the matrix elements. The theory includes the coupling of the various Zeeman sublevels by spontaneous emission and by the interaction with the two beams, and takes into account the finite value of the Doppler width.
In a double resonance experiment with a strong pump beam and a weak probe beam multiplet structures due to the AC Stark effect can be observed. The authors report the first observation of such a multiplet in a three-level experiment. The linearly polarised beams from a CW dye laser and a I 2 stabilised He-Ne laser were counter-propagating in the neon discharge cell and the saturating laser frequency was tuned across the resonances. The quadruplet structure was observed both for zero and for non-zero detuning delta 2 of the probe beam. The corresponding calculations for the three-level system with degenerate levels have been performed using the density matrix formalism with a tensorial expansion of the matrix elements. The theory includes the coupling of the various Zeeman sublevels by spontaneous emission and by the interaction with the two beams, and takes into account the finite value of the Doppler width.
For pt.I see ibid., vol.12, no.12, p.1939 (1979). The modulated fluorescence in an optical double resonance experiment, i.e. when an atom interacts with two intense monochromatic laser beams each of which is weakly modulated in amplitude at frequency Omega , is studied in detail. The modulation rate corresponding to the steady-state population of the highest atomic level exhibits resonant structures at the modulation frequencies Omega =0, +or- alpha 0 , +or-2 alpha 0 due to the dynamical Stark splitting of the various energy levels; alpha 0 being related to the Rabi frequencies alpha 1 and alpha 2 associated with the two lasers and the two atomic transitions, by alpha 0 2 = mod alpha 1 mod 2 + mod alpha 2 mod 2 . The peak at Omega =+or- alpha 0 is the most intense and exhibits splitting when the applied fields are detuned from exact resonance with the respective atomic frequencies. Resonances are observed in the modulation rate of the intermediate-level population at the modulation frequencies Omega =0, +or-2 alpha 0 . In the presence of detunings of the applied fields, additional resonant structures occur at Omega =+or- alpha 0 which increase in magnitude with higher detunings and split. Explicit expressions for the positions, widths and weights of these resonant components are obtained analytically for intense, resonant fields. Numerical results for general values of the laser field strengths and the detunings are given.
The effect of an intense pump beam on the intensity of the phase-conjugated emission is studied in the case of a three-level atom. We first extend to the case of cross-polarized pump beams the dressed-atom model that we have presented previously [Phys. Rev. A 34, 4008 (1986)] for the case of two-level atoms. The range of validity of our theory is \ensuremath{\Gamma} (natural width) ${\ensuremath{\Omega}}_{1}$ (Rabi frequency of the intense pump) ku (Doppler width). We have studied the line shape in degenerate four-wave mixing, the influence of a static magnetic field, and the resonances that appear in nondegenerate four-wave mixing. Experiments are done in a neon discharge using cw dye lasers. The experimental results are in good agreement with the theoretical predictions. In degenerate four-wave mixing, we have shown that the saturating dip disappears when the weak beams have orthogonal polarizations. In the presence of a static magnetic field and in the nearly degenerate case, narrow resonances corresponding to transitions between energy levels of the dressed atom are observed. The intensity and the width of these resonances are in very good agreement with the predictions of the theoretical model.
Autler-Townes (A-T) splitting, known as an AC Stark effect, shows a change of an absorption/emission spectral line of a probe beam when an oscillating field is tuned in resonance with the atomic or molecular transition. The A-T splitting is observed in different three-level atoms and widely investigated in a vapor cell and in a magneto-optical trap (MOT). The A-T splitting plays an important role in the atom-based microwave electric-field measurements where a cascade three-level system involving Rydberg state is adopted. In this work, an A-T splitting is observed in an ultracold cesium Rydberg gas, which is cooled down to about 100 pK and center density is about 1010 cm-3 in a conventional MOT by using the laser cooling technology. We present the A-T spectrum in a ladder three-level atomic system involving a 34D5/2 Rydberg state. The cesium ground state (6S1/2), excited state (6P3/2) and Rydberg state (34D5/2) constitute a Rydberg three-level system. A coupling laser, locked to the Rydberg transition by using a Rydberg electromagnetically induced transparency signal that is obtained from a cesium room-temperature vapor cell, couples 6P3/2 (F'=5) 34D5/2 Rydberg transition. A weak probe laser, stabilized to a ground-state transition by using a polarization spectroscopy, is swept, covering the transition 6S1/2 (F=4) 6P3/2 (F'=5) with a double-passed acousto-optic modulator. The probe and coupling lasers are counter-propagated through the MOT center. The power of probe light is 200 pW, corresponding Rabi frequency p=21.05 MHz. During the experiment, 50 s after turning off the trapping laser, both the coupling and probe beams are switched on and last 100 s. The A-T spectrum as a function of the probe detuning is detected with a single-photon counter module detector. We use Gaussian multiple peak fitting to obtain the positions of the A-T peaks and the A-T splitting. The measured A-T splitting is proportional to the Rabi frequency of the coupling light. We numerically solve the density matrix equations to obtain the A-T spectrum, and the calculations reproduce A-T spectra well. The measured A-T splitting shows good agreement with the theoretical calculation for Rabi frequency of the coupling light c29 MHz. The A-T splitting is less than the calculation for the case of c29 MHz, the deviation is mainly attributed to the increased dephasing rate induced by the strong interaction between Rydberg atoms, whose number increases with the coupling laser Rabi frequency. In this work, the adopted method for the cascade three-level system involving Rydberg state is also suitable for -and V-type cases.
We have calculated the steady-state intensity of fluorescence emitted from the middle and upper levels of a three-level (J=0\ensuremath{\rightarrow}1\ensuremath{\rightarrow}0) atomic ladder system subjected to a weak probe laser tuned to the transition between the lower two levels and a strong laser tuned to the transition between the upper two levels. This configuration of strong and probe lasers is the reverse of that used in previous experimental studies of three-level ladder systems. The configuration studied in this paper allowed the investigation of the population of both levels coupled by the strong laser. In order to predict in detail the results of a real, nonideal experiment carried out on a J=0\ensuremath{\rightarrow}1\ensuremath{\rightarrow}0 three-level system in a barium atomic beam, the theoretical model must include the effects of the experimental geometry, Zeeman degeneracy, hyperfine structure, and isotope structure. The experiment and the model were restricted to the case where both lasers have the same linear polarization. The method of Ben-Reuven and Klein was used to find an analytic solution to the Bloch equations for the three-level system. Without an analytic or semianalytic solution, the extension of the theory to describe a real experiment would have required a prohibitive amount of computer time.
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.