Modulational instability and pattern formation in the field of noncollinear pump beams

We study pattern formation that is due to modulational instability of noncollinear counterpropagating beams. Angular misalignment of the pumps over a broad range leads to the generation of lines oriented perpendicular to the plane of the pump beams. A theoretical expression for the angular separation of the lines is in close agreement with observations. Outside this range, for both small and large misalignments, we observe squeezed hexagonal patterns. (C) 1997 Optical Society of America.