“…This noise signal interacts with the pump beam, and grows into a strong coherent signal. This phenomenon is commonly observed in stimulated Brillouin scattering involving high-power pulsed laser [32,33], and in photorefractive materials with low-power cw lasers [34,35]. More recently, self-pumped phase conjugation effect has also been observed in resonant media, using frequency shifted signal and pump fleld [36], or degenerate four-wave mixing process [37].…”