A coupled-mode theory is developed for photorefractive hologram sharing in mutually pumped phase conjugators. The theory shows that the spatial gain coefficients for the mutually conjugated beams are twice as large as those of other scattered beams.
Pochi Yeh, "Coupled-mode theory of hologram sharing in mutually pumped phase conjugators," Appl. Opt. 28, 1961-1964 (1989)