Transition from Backscattering Speckles to Phase Conjugation in LiNbO₃:Fe

We investigate the backscattering for converging beams in iron-doped lithium niobate crystals. Due to the nonlinear properties of the crystal, backscattering exhibits temporally fluctuating speckles that make a transition to the phase conjugate of the incident beam under certain circumstances. Our observation seems to point to a new kind of self-pumped phase conjugation in photorefractive media.