Inherent contradictions in the tunneling-multiphoton dichotomy

Strong-field phenomena are currently described as being multiphoton or tunneling, based on whether the Keldysh parameter {gamma} is greater than or less than unity. There are disqualifying features in this categorization. It is specific to the length gauge, dependent on only one intensity parameter,...

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Bibliographic Details
Published in:	Physical review. A, Atomic, molecular, and optical physics Vol. 75; no. 3
Main Author:	Reiss, H. R.
Format:	Journal Article
Language:	English
Published:	United States 29-03-2007
Subjects:	APPROXIMATIONS ATOMIC AND MOLECULAR PHYSICS DIPOLES MULTI-PHOTON PROCESSES PHOTOIONIZATION PHOTON-ATOM COLLISIONS POTENTIALS STRONG INTERACTIONS TUNNEL EFFECT
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Summary:	Strong-field phenomena are currently described as being multiphoton or tunneling, based on whether the Keldysh parameter {gamma} is greater than or less than unity. There are disqualifying features in this categorization. It is specific to the length gauge, dependent on only one intensity parameter, and backward in the sense that ionization with {gamma}>>1 can occur only by tunneling, and ionization with {gamma}<<1 must be over the barrier, and hence is not achieved by tunneling. As {gamma} becomes smaller, ionization becomes increasingly distant from tunneling, and eventually reaches conditions where the dipole approximation fails and there is no meaningful scalar-potential diagram at all.
ISSN:	1050-2947 1094-1622
DOI:	10.1103/PhysRevA.75.031404