Abstract
We observed unexpected modulation in both the spectrum and temporal shape of the amplified signal
pulse from a non-collinear parametric amplifier (NOPA). By analyzing the time course of the spectrum,
we could prove that the main contribution to the spiky spectrum in the NOPA output is the stimulated
Raman process. The modulation is explained by the contribution of the stimulated Raman scattering,
induced by a high peak intensity amplified signal pulse, leading to non-ideal pulse compression. This
may create a serious problem in the construction of OPA and OPO, particularly for NOPAs used for
studying ultrafast processes. The obtained results demonstrate that care must be taken when obtaining
the shortest pulse from the NOPA, with reproducible smooth spectral and temporal shapes, by avoiding
Raman gain/loss processes.
