Parametric Raman gain suppression in D_2 and H_2

We report direct experimental evidence of the absence of exponential gain at the Stokes wavelength for Stokes/anti-Stokes phase-matched stimulated Raman scattering. The amplification of a Stokes seed pulse was measured at various propagation angles relative to the pump direction. Nonexponential growth was observed at the Stokes/ anti-Stokes phase-matching angle with an amplification that was smaller than at non-phase-matching angles by a factor of more than 10(7).