Spectroscopy dressed-states

Bandrauk s long-term research interests include the dressed-state representation of molecular spectroscopy. His contributions to the nonperturba-tive treatment of molecular spectroscopy from the weak field to strong field limits have been summarized in two chapters in a book he edited in 1993.286 Bandrauk and his coworkers published the first theoretical demonstration of the use of chirped pulses to effect laser bond breaking in less than a picosecond.287 His other firsts include the first prediction of molecular stabilization in intense laser fields288 and the first complete non-Born-Oppenheimer calculation of dissociative ionization of molecules in intense femtosecond laser pulses.289... 

A. D. Bandrauk, Ed., Dressed State Representation of Molecular Spectroscopy—Molecules in Laser Fields, Dekker, New York, 1993, Chapters 1 and 3. Nonperturbative Treatment of Molecular Spectroscopy from the Weak Field to Strong Field Limits Analytical and Numerical Methodology. 

In Section 9.3 we have used this truncated dressed state picture to discuss photoabsorption and subsequent relaxation in a model described by a zero-order basis that includes the following states a molecular ground state with one photon of frequency doorway state with no-photons, l, 0), and a continuous manifold of states /) that drives the relaxation. This model is useful for atomic spectroscopy, however, in molecular spectroscopy applications it has to be generalized in an essential way—by accounting also for molecular nuclear motions. In the following section we make this generalization before turning to consider effects due to interaction with the thermal environment. 

It should be noted that instead of dressing the molecular states g and s by 1 and 0 photons, respectively, we could use any photon numbers p and p — 1. The corresponding matrix elements are than proportional to p. In processes pertaining to linear spectroscopy it is convenient to stick with photon populations 1 and 0, keeping in mind that all observed fluxes should be proportional to the incident photon numberp or, more physically, to the incident field intensity fo P- With this in mind we will henceforth use the notation g, k) (or g, m if the incident direction is not important for the discussion) as a substitute for g, Ik)-... 

The AC Stark effect is relevant, not only in atomic spectroscopy, but also in solid state physics. The biexciton state (or excitonic molecule), where two Wannier excitons are bound by the exchange interaction between electrons, occurs in various semiconductors (see section 2.22). Various experiments on the AC Stark effect of excitons have been reported, but the clearest example to date is probably the observation of the Rabi splitting of the biexciton line in CuC reported by Shimano and Kuwata-Gonokami [477]. It is very interesting to consider how Bloch states in solids, which themselves are delocalised and periodic, are dressed or modified by the electromagnetic field, since their properties are rather different from those of purely atomic states, which are by definition completely localised. 

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