  It is important to re-examine some of the interactions of gravitational waves
with matter due to the recent discovery of the waves in LIGO. In a previous
paper with Morales, interaction of gravitational waves was studied with scalar
and neutrino fields in Minkowski space-time. In this paper, we find that
electromagnetic waves have a similar interaction with gravitational wave in a
flat background, and we comment on the implications of this for a gravitational
wave detector. Primordial gravitational waves were generated in the early
universe and thus it is important to study interaction of the gravitational
waves in cosmological backgrounds. In this paper we discuss the interaction of
electromagnetic waves and gravitational waves in a de-Sitter background. We
find that the electromagnetic wave is perturbed and modulated. This result is
new and will be useful in studying inhomogeneities in Cosmic Microwave
Background.
