Self-pumped phase conjugation is generally believed to be attributed to degenerate four-wave mixing. Accordingly, the phenomenon requires the existence of three waves at certain interaction regions for the excitation of the fourth one. Although this condition is not satisfied by a train of femtosecond pulses with a repetition rate of 110 MHz, we have observed self-pumped conjugate pulses retroreflected by a BaTiO3 crystal. The conjugate character of the pulses is demonstrated with the distorter method. (C) 1996 Optical Society of America
