180 / 2025-03-18 12:34:58

Coupling mechanisms of Stimulated Brillouin Scattering in Two-Color Lasers with large frequency difference

stimulated Brillouin scattering; two-ion acoustic decay; ion acoustic wave; laser plasma instability.

Effective control of stimulated Brillouin scattering (SBS) is an important cornerstone for realizing high-gain laser fusion. Numerous studies have shown that two-color and multi-color broadband light can reduce SBS, but most studies have focused on the case of small frequency differences (). The coupling of SBS mainly comes from the direct coupling of the laser field. In the case of large frequency differences, this coupling mechanism fails. We proposed a mechanism coupling the stimulated Brillouin scattering (SBS) of two-color lasers with wavelengths of 527nm and 351 nm via the two-ion decay instability (TID). TID refers to the process in which a large-amplitude ion acoustic wave (IAW) decays into two other IAWs with longer wavelengths. This leads to the weakening of the IAW in the SBS process, thereby reducing the laser reflectivity. It was found that an IAW excited by a 527nm laser can seed the decay of an IAW excited by a 351nm laser, promoting the latter IAW decay into the former IAW, thereby adjusting the SBS from both lasers and resulting in a decrease in the total reflectivity. As the fraction of the 527nm laser increases, the total SBS reflectivity first decreases and then increases. When   is about 20%-30%, the energy reflectivity of the two lasers are approximately equal, and SBS has the minimum total reflectivity. Through this mechanism, the incidence of two-color laser can achieve lower reflected energy than monochromatic laser with the same total intensity. In addition, the effect of this coupling mechanism is enhanced with the increase of the total laser intensity. These results demonstrate the application potential of replacing a small fraction of high-frequency light with low-frequency light in mitigating laser plasma instabilities.