Critical slowing-down in photorefractive scattering below the self-oscillation threshold

Summary form only given. Summary from only given. Photorefractive crystals may generate new optical beams of the same frequency as a pump wave if the appropriate optical feedback is ensured with external mirrors or with a special choice of the pump beam orientation. The onset of oscillation in these coherent oscillators is similar either to the second order phase transition or first order phase transition. We report on the study of the threshold behaviour of the semilinear coherent oscillator with two counterpropagating pump waves. The beam of an Ar+-laser (0.51 /spl mu/m) is used to pump a 3.6-mm thick BaTiO/sub 3/ sample (PRC).