  A novel and universal interference structure is found in the photoelectron
momentum distribution of atoms in intense infrared laser field. Theoretical
analysis shows that this structure can be attributed to a new form of
Coulomb-field-driven backward-scattering of photoelectrons in the direction
perpendicular to the laser field, in contrast to the conventional rescattering
along the laser polarization direction. This transverse backward-scattering
process is closely related to a family of photoelectrons initially ionized
within a time interval of less than 200 attosecond around the crest of the
laser electric field. Those electrons, acquiring near-zero return energy in the
laser field, will be pulled back solely by the ionic Coulomb field and
backscattered in the transverse direction. Moreover, this rescattering process
mainly occurs at the first or the second return times, giving rise to different
phases of the photoelectrons. The interference between these photoelectrons
leads to unique curved interference fringes which are observable for most
current intense field experiments, opening a new way to record the electron
dynamics in atoms and molecules on a time scale much shorter than an optical
cycle.
