We report on the observation of Raman gain suppression by parametric f
our-wave mixing in coherent Raman probe scattering with a noncollinear
pump and probe arrangement. The effect has been observed in coherent
Stokes scattering of picosecond pulses from polaritons in a LiIO3 crys
tal. The angular intensity pattern of Stokes probe scattering shows a
distinct dip in phase-matching directions of a noncollinear parametric
four-photon interaction K-L + K'(L) = K-S + K-A, where two photons at
the laser frequency, one from the pump beam and another one from the
probe beam scatter into Stokes and anti-Stokes photons. The interferen
ce between this process and Raman scattering results in an additional
dark ring in the angular intensity pattern of Stokes scattering of the
pump pulse. (C) 1998 Elsevier Science B.V. All rights reserved.