The occurrence of a periodic photo-induced grating having about 3.2-mu m period and modulation heights up to 150 nm is discovered here under the irradiation of 10-ns 1,064-nm laser pulses with Ag nano-particles deposited on ITO substrates. It is shown that the main role is played by the ITO resistance. This can be explained as the result of interaction between two coherent waves. The first wave is engendered by the fundamental laser and the second one is due to the two-photon absorption phenomenon. It is important mentioning that the observed photo-induced grating is obtained only from a treatment by single 10-ns laser pulses with an effective pump power below 0.7 GW/cm(2). Since the laser power densities are markedly low and the pulse durations larger than those of the femtosecond laser, the origin of this result is expected to be ascribed to the plasmon excitation leading to further thermoionization.