Reducing the total stimulated brillouin scattering of two-color lasers through two-ion decay

Abstract

A mechanism coupling the stimulated Brillouin scattering (SBS) of two-color lasers with wavelengths of 527 and 351 $\mathrm{nm}$ via the two-ion decay instability is proposed. When the SBS reflectivities of both lasers exceed 10%, the ion-acoustic wave excited by the 527 $\mathrm{nm}$ laser seeds the decay process of the ion-acoustic wave excited by the 351 $\mathrm{nm}$ laser, thereby promoting the decay of the latter into the former. This results in a significant reduction in the SBS reflectivity of the 351 $\mathrm{nm}$ laser, while the SBS of the 527 $\mathrm{nm}$ laser exhibits minimal variation, consequently reducing the total SBS reflectivity. The total SBS reflectivity initially decreases and then increases as the intensity fraction α of the 527 $\mathrm{nm}$ laser rises. When $\alpha \sim (20\%{-}30\%)$ , the laser energy reflections from both lasers become approximately equal, achieving the minimum total reflectivity. Through this mechanism, the incidence of the two-color lasers can achieve lower reflected energy compared to monochromatic lasers with the same total intensity. These results demonstrate the significant potential of replacing a small fraction of high-frequency light with low-frequency light in enhancing the laser-target coupling efficiency for inertial fusion energy.

Keywords

• stimulated brillouin scattering
• two-ion decay
• parametric instability
• two-color laser
• ion acoustic wave
• laser plasma instability