  Normal broadband lasers with collinear polychromatic components have immense
potential for mitigating laser plasma instabilities (LPIs). However, the
projection complexity of collinear polychromatic light (CPL) is a significant
challenge owing to the demand for a large bandwidth and beamlet number. Here,
we propose a theoretical LPI model and optical design for non-collinear
polychromatic light (NCPL), which has a small angle $\sim4^\circ$ and large
frequency difference $\sim$1\% between the double-color beamlets. LPI models of
the NCPL demonstrate a decoupling threshold for the shared daughter waves under
a multibeam configuration. Compared with the CPL, the wavevector couplings are
further reduced by the introduced angle. Therefore, both the growth rate and
saturation level of LPIs are greatly reduced by using the NCPL. The two- and
three-dimensional simulation results indicate that the NCPL reduces the
absolute and convective decoupling thresholds of the CPL and is sufficient to
effectively mitigate the reflectivity, hot-electron generation, and intensity
of cross-beam energy transfer. An optical design for the efficient generation
of ultraviolet NCPL has been presented based on the unsaturated optical
parametric amplification and non-collinear sum-frequency generation.
