We propose a magnetooptical biprism that can be used for coherent spli
tting of atomic beams into two spatially separated components. To crea
te such a biprism, we use a triangular potential corresponding to a pe
riod of a magnetooptical grating with enlarged spacing. The main advan
tage of the proposed biprism over conventional magnetooptical gratings
is that such a biprism allows a considerable increase in the angle of
splitting in the Raman-Nath regime.