Field dressed

Consider a molecule prepared in the absolute ground state in the absence of the field and subjected to microwave field of frequency . If collided with a structureless atom in the absence of the field and at collision energies below the first excitation threshold, the molecule can undergo only elastic scattering. In the presence of the field, the ground state of the molecule becomes a field-dressed state X). And for every field-dressed state X), there is an infinite number of replica states 2 - A ), lower in energy. The states 2 - A ) and X) are coupled by the anisotropy of the atom-molecule interaction potential, so collisions can induce... 

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... 

As explained in Section 6.2, m(a>) is that part of the polarizability tensor that resultiS from the interference between the two paths associated with the field-dressed ener M E. It is a function of the cfc2 coherence between the two states that make up Miff superposition state in Eq. (12.65). By contrast, a"(tv) denotes the ordinary polar li ability tensor, resulting from noninterfering terms. It is only a function of the poph-lt lations, cj 2 and c2 2, of the Ej) and E2) states. 

Figure 22 The populations, given as St (t) s ( . (t) 0(O) 2, of the field dressed states, given that iff (t = 0)) = 1) and

The emergence in the late 1980s of chirped pulse amplification techniques [1] meant that it was now possible to produce focused laser intensities well in excess of 10 W/cm. This is equivalent to a laser electric field approaching one atomic unit and it is perhaps not surprising, therefore, that conventional perturbation theory cannot be applied to the dynamics of atoms and molecules in such intense laser fields. In fact these fields dress the electrons and nuclei on a timescale that is short compared to those of conventional atomic or molecular processes and new non-linear phenomena are observed. 

Figure 22 displays the evolution of the populations Si it) = Eiit) ili(0) P of the field dressed states, having started with i/f it = 0)) = 1). The parameters are as in Fig. 21, with

avoided crossing region, where... 

Electromagnetic Field-Dressed Diabatic and Adiabatic Potential Energy Curves. 177... 

It is convenient to treat intense electromagnetic field problems in the dressed molecular states picture (see review by Giusti-Suzor, et al, (1995)). This picture allows one to think about intense field problems in a framework that closely resembles the weak field, diabatic or adiabatic states picture that is the primary focus of this book. In the dressed states picture the photon energy is added to, or subtracted from, the field-free potential energy curves. One obtains field-dressed potential curves. 

The electromagnetic radiation field is taken into account by adding the energy of the photons to the various molecular potential curves, Vi(R). If the photon number is initially N, when n photons are absorbed, the remaining number of photons is N — n. The resultant field-dressed diabatic state has potential energy... 

Each field free potential curve, V (R), generates a family of field-dressed potentials, Vj>n(iJ), with the result that many intersections between potential curves occur that are not present in the field-free case. The spectroscopic and dynamical consequences of these field-dressed curve crossings are understood using exactly the same methods presented in this book for field-free intersecting potentials. 

Figures 3.11 and 3.12 illustrate the weak-field and field-dressed pictures of photodissociation of the Hg molecular ion. In Fig. 3.11, one-, two-, and three-photon transitions from v = 2 of the X2 +(1si7s) bound state to the 2 (2pcru) continuum are shown. The 1- and 3-photon transitions are electronically u — g allowed, but, in a perturbative picture, the 1-photon transition has a vastly smaller Franck-Condon factor than the 3-photon transition. The 2-photon transition to the 2E+ state is (g u)forbidden, but the 2E+ state acts as a virtual...

Figure 3.12 shows that the X2 + n = 0 curve is predissociated radiatively by the dressed 2 + n = 1 and n = 3 curves. The coupling between the crossing, field-dressed, diabatic states (solid curves in Fig. 3.12) is the radiative interaction,... 

Figure 3.12 Field-dressed potential energy curves for HJ interacting with a 532nm laser field. The field-dressed diabatic curves are shown as full lines. The field-dressed adiabatic curves, shown as dotted and dashed curves, correspond respectively to laser intensities of 1 x 1013 W/cm2 and 4 x 1013 W/cm2 (from Giusti-Suzor, et al., 1995).

Figure 33. Same as Fig. 32 but for an excitation from an initial field dressed state being displaced in comparison to the field free state. An effective selective counterclockwise rotation is induced. 

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... 

Figure 2.1 Field-dressed potential energy curves of Hj (X = 532 nm), in the diabatic (solid lines) and adiabatic (broken lines for / = 10 W/cm and dotted lines for / = 5 x 10 W/cm ) frames. Curve-crossing regions are outlined by rectangular boxes XI, X2, and X3. The energies of the v = 2,4, 5 vibrational levels are indicated by thin horizontal lines.

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