Ion exchange method for obtaining second-order nonlinearity in glass

In this work, we propose two-step process to create a second-order nonlinearity in glasses. First, we use the ion exchange method to form a region of an ion concentration and, consequently, conductivity gradient in glass.  Afterwards, we apply DC voltage to the specimen at room temperature. This causes formation of non-equilibrium charge and inner electrostatic field, which induces effective second-order optical nonlinearity of the glass that exceeds  one of thermally poled glass sample. After turning the voltage off, the effect gradually degrades within a few hundreds of seconds. Comparison of silver-for-sodium and potassium-for-sodium ion exchanges shows that in the latter  case the result nonlinearity has longer relaxation time.