Strong field physics

Mohr, P.J. (1992) Self-energy correction to one-electron energy levels in a strong Coulomb field. Physical Review A, 46, 4421-4424. 

In the following, we will discuss two basic - and in a sense complementary [44] - physical mechanisms to exert efficient control on the strong-field-induced coherent electron dynamics. In the first scenario, SPODS is implemented by a sequence of ultrashort laser pulses (discrete temporal phase jumps), whereas the second scenario utilizes a single chirped pulse (continuous phase variations) to exert control on the dressed state populations. Both mechanisms have distinct properties with respect to multistate excitations such as those discussed in Section 6.3.3. 

For a recent review and guide to the literature, see T.E. Cowan and J.S. Greenberg in Physics of Strong Fields edited by Walter Greiner (Plenum,... 

The situation changes drastically, however, if we irradiate the surface state electrons with a sufficiently strong microwave field. Strong fields change the physics of the SSE system profoundly, eventually driving it into chaos. That chaos can indeed occur in the SSE system was first demonstrated by Jensen in 1982. The system he proposed is shown in Fig. 6.1(b). It is an extension of the system shown in Fig. 6.1(a). A microwave field is applied perpendicular to the helium surface S such that the field direction is parallel to the x direction. The resulting classical Hamiltonian of the combined SSE plus microwave field can be written as... 

The data shown in Fig. 6.9 and Fig. 6.10 confirm our suspicion that for weak microwave fields no chaos mechanisms have to be invoked for an adequate physical understanding of microwave ionization data. The situation, however, is quite different in the case of strong microwave fields. In this case the ionization routes are very comphcated, and the multiphoton pictmre loses its attractiveness. It has to be replaced by a picture based on chaos. Chaos provides a simpler description of the ionization process and consequently a better physical insight. The discussion of the chaotic strong-field regime is the topic of the following section. 

Excellent reviews exist addressing the topic of chaos in atomic physics. The most comprehensive attempt at a review of the entire subject of quantum chaology and applications is a recent collection of reprints and original articles edited by Casati and Chirikov (1995). Its section on atoms in strong fields especially is highly relevant for the topic of this book. Additional material on chaos and irregularity in atomic physics can be found, e.g., in a collection of articles edited by Gay (1992). 

The remainder of this chapter is organised as follows. First, we briefly describe a typical system which has been used to achieve intense fields, the purpose being to stress the experimental connection between high laser fields and short pulses. We move on to describe various high field effects, together with simple physical explanations which have been used to interpret them. We then return to our main discussion about the role of atomic physics in these effects and, finally, to the description of a theoretical picture which holds promise to describe the response of many-electron atoms in strong fields. 

The subject of quantum optics is concerned with the quantum properties of the radiation field, i.e. the properties of photons. Since the word multiphoton has been used, it might seem that strong laser fields are in some way relevant to quantum optics. However, the word multiphoton is something of a misnomer in the strong field regime. In fact, if very many photons are involved, quantisation of the radiation field is more or less irrelevant the intense, coherent laser pulse tends to a quasiclassical beam of light. Indeed, it has been pointed out by several authors [483] that the use of the word photon in the context of laser physics is of questionable validity. 

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