  A new evolution pattern for parametric instabilities in the non-linear stage
driven by a broadband laser is studied with kinetic particle-in-cell
simulations. It is found that an intermittent excitation of parametric
instabilities caused by the high-intensity pulses, which are generated by the
laser intensity variation of the broadband laser. The synergism between these
high-intensity pulses reduces the Landau damping through the co-propagation of
the electron-plasma waves and hot electrons, promoting the transition from
convective to absolute stimulated Raman scattering. These intermittently
excited parametric instabilities, especially absolute instability, will produce
over-expected hot electrons compared with linear theory. However, comparisons
between the energy of scattered lights for various bandwidth lasers indicate
suppression of parametric instabilities with large laser bandwidths. Our works
provided an opportunity to advance the understanding of the broadband
laser-plasma interaction.
