Db. Milosevic, ON-SHELL AND OFF-SHELL LOW-FREQUENCY APPROXIMATIONS FOR POTENTIAL SCATTERING IN A STRONG LASER FIELD - OPTICAL THEOREM AND SUM-RULE, Journal of physics. B, Atomic molecular and optical physics, 28(9), 1995, pp. 1869-1887
We present analytical and numerical results for the T matrix and cross
sections (differential and total) for scattering in a strong low-freq
uency laser field. Presented results, based on recently derived expres
sions for the off- and on-shell low-frequency T matrices are beyond th
e first Born approximation results of Daniele ef al for scattering on
the Yukawa potential in a laser field. An analytical expression for th
e total cross section is obtained using the [1, 1] Pade approximant to
the off-shell low-frequency T matrix. This result explicitly shows de
parture from the sum rule and it is analysed as function of the laser
field intensity and polarization angle. If the laser field is so stron
g that the laser field induced scattering particle impulse eA(0) is co
mparable with the initial impulse pi this departure has a maximum. For
an ultra-strong laser field (eA(0)>>p(i)) the total cross section is
small in comparison with the field-free section, i.e. the influence of
the scattering potential is weak. The results for different values of
the screening radius are also presented and it is observed that the d
eparture from the sum rule is larger for long-range potentials (when t
he interplay between the potential and the intense radiation field is
important). The departure is strong for small values of the polarizati
on angle (Theta(i)<20 degrees) and weak for 45 degrees<Theta(i)<135 de
grees.