Observation of the photoinduced conductivity in a regular domain structure with tilted walls in MgO:LiNbO$_3$ at a wavelength of 632.8 nm at Bragg diffraction

A 632.8-nm radiation-induced change in the conductivity of a regular domain structure (RDS) formed in a $5\%$ MgO:LiNbO$_3$ crystal has been detected for the first time. As a result, the relaxation rate for the Bragg diffraction efficiency on the RDS, which is observed after the application of an external electric field, increases with the intensity of a probe beam. This dependence is linear in the initial stage of relaxation caused by the screening of the external field because of the redistribution of charges over tilted conductive domain walls of the RDS. For the probe beam with an intensity of $49$ mW/mm$^2$, the induced effective conductivity of the RDS, which is estimated as $\sigma_{\text{eff}}=3.5\times10^{-9}\Omega^{-1}$m$^{-1}$, is more than four orders of magnitude higher than the dark conductivity of the single-domain MgO:LiNbO$_3$ sample.