Linewidth compression and measurement in BBO crystal optical parametric generation and amplifier

In this paper, we present a detailed computer simulation of the linewidth in optical parametric generator and amplifier caused by the divergence angle of pumping, linewidth of pumping beam, off axis phase matching, high gain coefficient of nonlinear optical (NLO) crystal. It is shown that the linewidth of parametric light is very narrow far away from the degeneracy point, and the linewidth begins to large quickly at the degeneracy point. And the off axis pumping and the divergence angle of pumping beam influenced the signal linewidth more quickly than those of other factors did. The signal linewidth to control less than 0.3nm in experiments are obtained.