  We theoretically investigate nonresonant spontaneous bremsstrahlung in the
scattering of an electron by a nucleus in the field of two linearly polarized
light waves propagating in the same direction in the general relativistic case.
It is demonstrated that there are two substantially different kinematic ranges:
the noninterference range, where the Bunkin-Fedorov quantum parameters serve as
multiphoton parameters,and the interference range, where interference effects
become significant, and quantum interference parameters play the role of
multiphoton parameters. We determine the cross sections of electron-nucleus
spontaneous bremsstrahlung in these kinematic ranges. It is demonstrated that
the partial cross section in the interference range with emission (absorption)
of photons at combination frequencies may considerably exceed the corresponding
cross section for any other geometry.
