He in dichromatic weak or strong ac fields of lambda(1)=248 nm and lambda(2) = (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	2014-03-01T01:51:09Z
dc.date.available	2014-03-01T01:51:09Z
dc.date.issued	2001	en
dc.identifier.issn	1050-2947	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/26239
dc.subject.classification	Optics	en
dc.subject.classification	Physics, Atomic, Molecular & Chemical	en
dc.subject.other	2-COLOR MULTIPHOTON IONIZATION	en
dc.subject.other	ABOVE-THRESHOLD IONIZATION	en
dc.subject.other	INTENSE LASER FIELD	en
dc.subject.other	UNIMOLECULAR REACTIONS	en
dc.subject.other	ANGULAR-DISTRIBUTIONS	en
dc.subject.other	PHASE-CONTROL	en
dc.subject.other	PHOTOIONIZATION	en
dc.subject.other	FREQUENCIES	en
dc.subject.other	EXCITATION	en
dc.subject.other	HYDROGEN	en
dc.title	He in dichromatic weak or strong ac fields of lambda(1)=248 nm and lambda(2) = (1/m) 248 nm (m=2,3,4)	en
heal.type	journalArticle	en
heal.identifier.secondary	013411	en
heal.language	English	en
heal.publicationDate	2001	en
heal.abstract	We have computed multiphoton ionization rates for He irradiated by a dichromatic ac held consisting of the fundamental wavelength lambda = 248 nm and its second-, third-, and fourth-higher harmonics. The intensities are in the range 1.0 x 10(12)-3.5 x 10(14) W/cm(2), 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, for S-1, P-1, D-1, F-1, (1)G, and H-1 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, Delta (w(1).F-1;omega (2),F-2,phi (2)), and the imaginary part is the multiphoton ionization rate, Gamma(omega (1),F-1;omega (2),F-2,phi (2)), where omega is the frequency. F is the field strength, and phi (2) is the phase difference. Through analysis and computation we show that, provided the intensities are weak, the dependence of Gamma(omega (1),F-1;omega (2),F-2,phi (2)) on phi (2) is simple. Specifically, for odd higher harmonics, Gamma varies linearly with cos(phi (2)) whilst for even higher harmonics it varies linearly with cos(2 phi (2)). 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 (omega (1),F-1) and (omega (2),F-2) is such that higher powers of cos(omega (2)) and cos(2 omega (2)) become important, these rules break down and we reach the strong-field regime.	en
heal.publisher	AMERICAN PHYSICAL SOC	en
heal.journalName	PHYSICAL REVIEW A	en
dc.identifier.isi	ISI:000166383000085	en
dc.identifier.volume	6301	en
dc.identifier.issue	1	en