The electric dipole approximation and the calculation of free-free transition matrix elements in multiphoton processes

Mercouris, Th; Komninos, Y; Dionissopoulou, S; Nicolaides, CA

dc.contributor.author	Mercouris, Th	en
dc.contributor.author	Komninos, Y	en
dc.contributor.author	Dionissopoulou, S	en
dc.contributor.author	Nicolaides, CA	en
dc.date.accessioned	2014-03-01T01:46:15Z
dc.date.available	2014-03-01T01:46:15Z
dc.date.issued	1997	en
dc.identifier.issn	09534075	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/24874
dc.title	The electric dipole approximation and the calculation of free-free transition matrix elements in multiphoton processes	en
heal.type	journalArticle	en
heal.identifier.primary	10.1088/0953-4075/30/9/014	en
heal.identifier.secondary	http://dx.doi.org/10.1088/0953-4075/30/9/014	en
heal.publicationDate	1997	en
heal.abstract	In view of the arguments put forward by van Enk et al, we discuss aspects of the theory of atom-laser field interactions as they relate to the calculation of properties for which free-free transitions play a significant role. Our conclusion is that: (i) according to the standard definition of the electric dipole approximation, which is what has been employed until now in all non-perturbative calculations of multiphoton processes, the on-energy shell singularity for the length and velocity gauges is real when the one-electron continuum is represented rigorously by energy-normalized scattering functions. On the other hand, the acceleration gauge does not give rise to this singularity. (ii) When the full coupling operator A(r) · p + 1/2 A2(r) rather than A(r) · p is used, the singularity persists for the electric dipole as well as for the higher multipoles. (iii) The use of box-normalized basis sets only leads to a model space whereby even repeated (and computationally expensive) calculations with increasing box size lack intrinsic rigour and the certainty that convergence implies accuracy.	en
heal.journalName	Journal of Physics B: Atomic, Molecular and Optical Physics	en
dc.identifier.doi	10.1088/0953-4075/30/9/014	en
dc.identifier.volume	30	en
dc.identifier.issue	9	en
dc.identifier.spage	2133	en
dc.identifier.epage	2141	en