Ultraviolet irradiation effect on the third-order optical nonlinearity of CuCl-microcrystallite-doped glass

We investigate the effect of irradiation by a UV pulse laser on the third-order optical nonlinearity of CuCl-microcrystallite-doped glass as a function of the irradiation’s shot number, energy density per pulse, and wavelength. The response time τ is estimated from the luminescence decay time of the CuCl excitons. The absolute value of the third-order nonlinear susceptibility ${\chi }^{(3)}$ is measured by degenerate four-wave mixing. Values of both τ and ${\chi }^{(3)}$ decrease after UV irradiation. The figure of merit for the optical nonlinearity, ${\chi }^{(3)}/\alpha \tau ,$ where α is the absorption coefficient, is almost constant before and after UV irradiation and is approximately 500 esu cm s^-1 in the case of 8-nm CuCl microcrystallites. This value is 1 order of magnitude larger than that of ${\mathrm{CdS}}_x{\mathrm{Se}}_{1-x}$-microcrystallite-doped glasses. The mechanism by which τ and ${\chi }^{(3)}$ are decreased is discussed, considering defects levels formed at the interface between CuCl microcrystallites and glass matrix.