Gravitational Grating
  In this work, we study the interaction of the electromagnetic wave (EW) from
a distant quasar with the gravitational wave (GW) sourced by the binary stars.
While in the regime of geometric optics, the light bending due to this
interaction is negligible, we show that the phase shifting on the wavefront of
an EW can produce the diffraction pattern on the observer plane. The
diffraction of the light (with the wavelength of $\lambda_e$) by the
gravitational wave playing the role of {\it gravitational grating} (with the
wavelength of $\lambda_g$) has the diffraction angle of $\Delta\beta \sim
\lambda_e/\lambda_g$. The relative motion of the observer, the source of
gravitational wave and the quasar results in a relative motion of the observer
through the interference pattern on the observer plane. The consequence of this
fringe crossing is the modulation in the light curve of a quasar with the
period of few hours in the microwave wavelength. The optical depth for the
observation of this phenomenon for a Quasar with the multiple images strongly
lensed by a galaxy where the light trajectory of some of the images crosses the
lensing galaxy is $\tau \simeq 0.2$. By shifting the time delay of the light
curves of the multiple images in a strong-lensed quasar and removing the
intrinsic variations of a quasar, our desired signals, as a new method for
detection of GWs, can be detected.
