Stable High-Efficiency Double-Phase-Conjugate Mirror in a Cu-Doped Potassium Sodium Strontium Barium Niobate Crystal

We report a stable high-efficiency double-phase-conjugate mirror (DPCM) in a Cu-doped potassium sodium strontium barium niobate (KNSBN:Cu) crystal. The stable high phase-conjugate transmissivity reaches 55% when using a mW-order low-power Ar+ laser at a 514 nm wavelength with two mutually incoherent incident beams. The relative stability of the phase-conjugate transmissivity of as high as 93% was obtained in 150 minutes. The incident-location and angle responses of the phase-conjugate transmissivity were observed. Unstable behaviour of the DPCM was also observed and discussed.