  Optical responses of ferromagnetic materials with spin gauge field that
drives intrinsic spin curren is theoretically studied. The conductivity tensor
is calculated based on a linear response theory to the applied electric field
taking account of the non-linear effects of the spin gauge field to the second
order. We consider the case where the spin gauge field is uniform, realized for
spiral magnetization structure or uniform spin-orbit interaction. The spin
gauge field, or an intrinsic spin current, turns out to give rise to
anisotropic optical responses, which is expected to be useful to experimental
detection of magnetization structures.
