Db. Milosevic, OFF-SHELL AND ON-SHELL LOW-FREQUENCY APPROXIMATIONS FOR POTENTIAL SCATTERING IN A STRONG ELLIPTICALLY POLARIZED LASER FIELD, Physical review. A, 53(1), 1996, pp. 619-622
Applying an appropriate unitary transformation, a nonperturbative resu
lt for the T matrix for potential scattering in a strong elliptically
polarized laser field is derived. The approximation obtained is exact
in the high-intensity laser held limit. For lower laser field intensit
y, this result is an off-shell low-frequency approximation. The second
result is a modified on-shell low-frequency approximation. For an ell
iptically polarized laser field, the momenta shifts are complex, but e
nergies are still on shell. In the linear polarization case, these shi
fts are real and the range of applicability is substantially wider.