Dressed atom

Dalibard J and Cohen-Tannoudji C 1985 Dressed-atom approach to atomic motion in laser light the dipole force revisited J.Opt.Soc.Am. B 21707-20... 

To describe the shifts and intensities of the m-photon assisted collisional resonances with the microwave field Pillet et al. developed a picture based on dressed molecular states,3 and we follow that development here. As in the previous chapter, we break the Hamiltonian into an unperturbed Hamiltonian H(h and a perturbation V. The difference from our previous treatment of resonant collisions is that now H0 describes the isolated, noninteracting, atoms in both static and microwave fields. Each of the two atoms is described by a dressed atomic state, and we construct the dressed molecular state as a direct product of the two atomic states. The dipole-dipole interaction Vis still given by Eq. (14.12), and using it we can calculate the transition probabilities and cross sections for the radiatively assisted collisions. 

Using the dressed atomic states we construct the dressed molecular states as direct products. Explicitly, we construct the two states tpA(t) and tpB t) given by3... 

The dynamics of the dressed atom is determined by the effective one-mode time-dependent Schrodinger equation... 

G. Compagno, R. Passante, and F. Persico, Atom-Field Interactions and Dressed Atoms, Cambridge University Press, Cambridge, England, 1995. 

C. Dressed-Atom Model of the Amplification on Dark Transitions... 

Lee et al. [34] have shown that the physical origin of the cancellation of the central line in the spectrum can be explained clearly by the dressed-atom model of the system [35]. In this model we use a fully quantum-mechanical description of the Hamiltonian (65), which in a frame rotating with the laser frequency (0L can be written as... 

The dressed-atom predictions clearly explain the origin of the cancellation of the spectral line arising from the cancellation of the transition dipole moment due to quantum interference between the two atomic transitions. 

The dressed states are shown in Fig. 19a. We see that in the dressed atom basis the system is no longer a two-level system. It is a multilevel system with three different transition frequencies, dipole matrix elements iyN = (N,i ti j,N-l) ... 

Multiphoton processes taking place in atoms in strong laser fields can be investigated by the non-Hermitian Floquet formalism (69-71,12). This time-independent theory is based on the equivalence of the time-dependent Schrodin-ger description to a time-independent field-dressed-atom picture, under assumption of monochromaticity, periodicity and adiabaticity (69,72). Implementation of complex coordinates within the Floquet formalism allows direct determination of the complex energy associated with the decaying state. The... 

Fig. 8.34 Photon-assisted collisional energy transfer (a) molecular model (b) dressed-atom model...

In the atomic model (Fig. 8.34b, often called the dressed-atom model) [1090] the excited atom A absorbes a photon ho) of the transfer laser, which excites A further into a virtual state - -fuo that is near resonant with the excited state of B. The collisional energy transfer A -h -> B + AE kin with AE kin then proceeds with a much higher probability than the off-resonance process without photon absorption [1091]. 

C. Cohen-Tannoudji, S. Reynaud, Dressed-atom description of absorption spectra of a multilevel atom in an intense laser beam. J. Phys. B 10, 345 (1977)... 

An alternative description of the observed phenomena can be obtained by the dressed atom model [80]. In this approach the eigenvalues of the global system atom + field, the dressed states, are sought. The strong pump beam dresses the atom with laser photons which leads to energy levels split by the Rabi frequency. The resonances discussed in Fig. 20 then arise naturally as transitions between the (infinite) ladder of dressed states. The dressed atom model delivers a physically comprehensible description of atomic energy levels in strong fields and the reader is referred to Ref. 80 for a detailed presentation. 

The light shift of the resonance line of a single terrylene molecule was measured with a near-resonant pump (A > F) by either varying the pump intensity at a iked detuning or vice versa. As can be derived from a perturbative approach as well as from the dressed atom model, the light shift d for a near-resonant ptimp can be approximated (A > Qi) by the simple expression,... 

We now tackle the problem of the calculation of W2 and P for the 3-level atom described above, for which we shall use a dressed atom approach. Immediately after the detection of a first fluorescence photon at time t, the system is in the state = g,Ng,N >, i.e. atom in the ground state in presence of Ng blue photons and Ng red photons. Neglecting antiresonant terms, we see that this state is only coupled by the laser-atom interactions to the two other states = e3,Ng-l,Ng> and l4>2> eg,Ng,Ng-l> (the atom absorbs a blue or a red photon and jumps from g> to eg> or leg>). 

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