OFF-SHELL AND ON-SHELL LOW-FREQUENCY APPROXIMATIONS FOR POTENTIAL SCATTERING IN A STRONG ELLIPTICALLY POLARIZED LASER FIELD

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.