Backward beam fanning is numerically investigated with a two-dimensional model on the basis of the solution of the coupled-wave equations between the incident beam and the backward radiation scattered by the inhomogeneities or defects distributed throughout the crystals. The numerical results are consistent with our experimental observations in a crystal. The physical origin of backward beam fanning is that the coupling constant times the length of the crystal is above the threshold for amplification of the backward radiation but below the threshold for the generation of the phase conjugation by stimulated two-wave mixing.
© 1998 Optical Society of America
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