Means of sending a photon to an optically inactive photonic-band mode

We propose theoretically a means to send a photon to an optically inactive state at the $\Gamma$ point of the Brillouin zone of a photonic crystal. It is shown that by using the light scattering of attenuated-total-reflection (ATR) geometry, a combined system of a photonic crystal and a prism placed nearby, an optically inactive mode at the $\Gamma$ point can be excited. The excitation is demonstrated by calculating the ATR signal for a photonic crystal of spheres arrayed in a square lattice, which presents a distinct dip due to excitation of the inactive mode. To confirm that the excited mode is indeed the one of the $\Gamma$ point, we checked that equipartition of the energy of the excited mode is established among four diffracted plane waves associated with the four shortest reciprocal-lattice vectors of the excited Bloch wave.