He in dichromatic weak or strong ac fields of λ1 = 248 nm and λ2 = (1/m) 248 nm (m = 2,3,4)

Mercouris, T; Nicolaides, CA

dc.contributor.author	Mercouris, T	en
dc.contributor.author	Nicolaides, CA	en
dc.date.accessioned	2014-03-01T01:16:36Z
dc.date.available	2014-03-01T01:16:36Z
dc.date.issued	2001	en
dc.identifier.issn	10502947	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/14117
dc.subject.other	Eigenvalues and eigenfunctions	en
dc.subject.other	Electric field effects	en
dc.subject.other	Electronic structure	en
dc.subject.other	Heuristic methods	en
dc.subject.other	Irradiation	en
dc.subject.other	Photoionization	en
dc.subject.other	Photons	en
dc.subject.other	Spectrum analysis	en
dc.subject.other	Dichromatic fields	en
dc.subject.other	Multiphoton ionization	en
dc.subject.other	Helium	en
dc.title	He in dichromatic weak or strong ac fields of λ1 = 248 nm and λ2 = (1/m) 248 nm (m = 2,3,4)	en
heal.type	journalArticle	en
heal.identifier.primary	10.1103/PhysRevA.63.013411	en
heal.identifier.secondary	http://dx.doi.org/10.1103/PhysRevA.63.013411	en
heal.publicationDate	2001	en
heal.abstract	We have computed multiphoton ionization rates for He irradiated by a dichromatic ac field consisting of the fundamental wavelength λ = 248 nm and its second-, third-, and fourth-higher harmonics. The intensities are in the range 1.0 × 1012 - 3.5 × 1014 W/cm2, with the intensity of the harmonics being 1-2 orders of magnitude smaller. The calculations incorporated systematically electronic structure and electron correlation effects in the discrete and in the continuous spectrum, for1S,1P,1D,1F,1G, and1H two-electron states of even and odd parity. They were done by implementing a time-independent, nonperturbative many-electron, many-photon theory which obtains cycle-averaged complex eigenvalues, whose real part gives the field-induced energy shift, Δ(ω1,F1;ω2,F2,φ2), and the imaginary part is the multiphoton ionization rate, Γ(ω1,F1;ω2,F2,φ2), where ω is the frequency, F is the field strength, and φ2 is the phase difference. Through analysis and computation we show that, provided the intensities are weak, the dependence of Γ(ω1,F1;ω2,F2,φ2) on φ2 is simple. Specifically, for odd higher harmonics, Γ varies linearly with cos(φ2) whilst for even higher harmonics it varies linearly with cos(2φ2). These relations may turn out to be applicable to other atomic systems as well, and to provide a definition of the weak-field regime in the dichromatic case. When the combination of (ω1,F1) and (ω2,F2) is such that higher powers of cos(φ2) and cos(2φ2) become important, these rules break down and we reach the strong-field regime. ©2000 The American Physical Society.	en
heal.publisher	American Inst of Physics, Woodbury, NY, United States	en
heal.journalName	Physical Review A - Atomic, Molecular, and Optical Physics	en
dc.identifier.doi	10.1103/PhysRevA.63.013411	en
dc.identifier.volume	63	en
dc.identifier.issue	1	en
dc.identifier.spage	013411	en
dc.identifier.epage	013411	en