A Cu-doped (0.04 wt. %) (K0.5Na0.5)0.2(Sr0.61Ba0.39)0.9Nb2O6 crystal produced as much as 68% self-pumped phase-conjugate reflectivity at the laser wavelength-lambda = 514.5 nm. We also observed some phenomena that helped us to understand the mechanism for the self-pumped phase-conjugate mirror.