https://doi.org/10.1007/s100530170222
The multiphoton ionization rate and the energy shift of atoms interacting with weak dichromatic fields with commensurate frequencies are simple functions of the phase difference
1
Theoretical and Physical Chemistry Institute, National Hellenic Research
Foundation, 48 Vas. Constantinou Ave., 11635 Athens, Greece
2
Physics Department, National Technical University, Athens, Greece
Corresponding authors: a thmerc@eie.gr - b can@eie.gr
Received:
9
July
2000
Revised:
2
November
2000
Published online: 15 May 2001
By implementing a time-independent, nonperturbative many-electron, many-photon theory (MEMPT), cycle-averaged complex eigenvalues were obtained for the
He atom, whose real part gives the field-induced energy shift, 
, and the imaginary part is the multiphoton ionization rate, 
, where ω is
the frequency, F is the field strength and φ is the phase difference. Through analysis
and computation we show that, provided the intensities are weak, the dependence of
on φ is simple. Specifically, for odd harmonics, Γ varies linearly
with 
whilst for even harmonics it varies linearly with 
. In addition, this dependence on φ holds for 
as well. 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 
and 
is such that higher powers of and become important, these rules break down and we reach the strong field regime.
The herein reported results refer to 
and 
for He
irradiated by a dichromatic ac-field consisting of the fundamental wavelength 
nm and its 2nd, 3rd and 4th higher harmonics. The intensities are in the range
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, for 1S,
1P, 1D, 1F, 1G, and 1H two-electron states of even and odd parity.
PACS: 32.80.Rm – Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states) / 32.80.Fb – Photoionization of atoms and ions / 32.80.Qk – Coherent control of atomic interactions with photons
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2001
