Special analytical properties of ultrastrong coherent fields |
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Authors: | H R Reiss |
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Institution: | (1) Mathematical Institute, University of Oxford, 24/29 St. Giles', OX1 3LB Oxford, UK |
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Abstract: | Emerging ultrastrong-laser capabilities that can reveal details of vacuum
structure have intensified research into the fundamentals of quantum
electrodynamics. It has been more than half a century since relativistic
nonperturbative methods were introduced into the study of strong-field
phenomena. Much of the early progress remains of fundamental relevance, but is
known to only a small group of researchers. The aim of this paper is to reveal
some of that work and to show how it impacts on current investigations. A
basic result is that it has been shown that strong, single-mode fields (i.e.
laser fields) can be treated by relativistic quantum mechanics with results
identical to fully quantized electrodynamics. Attention is drawn to the
existence of a Volkov Green’s function that has a clear physical
interpretation as predicting several series of relativistic Floquet sideband
states. It is more transparent and informative than the Volkov Green’s
function of Schwinger. It is also shown that the fundamental experiments
performed at the Stanford Linear Accelerator Center in 1997 on
photon-multiphoton pair production could not be a high-order perturbative
result, as was presumed by the investigators. The intensity employed was
beyond the radius of convergence of perturbation theory, and the seeming
perturbative increase in rate with intensity is an artifact. Of particular
significance is the demonstration that a free electron in a strong plane-wave
field (a “Volkov electron”) exists in an
intensity-dependent superposition of angular momentum states, and is no longer
a simple spin-1/2 particle. |
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