The scattering of laser light due to cross-beam energy transfer (CBET) is an undesirable process in direct-drive inertial confinement fusion (ICF) that degrades both the compression and symmetry of the imploding target. Here, we present results from laser-plasma interaction simulations performed with the wave-based code LPSE that explore two techniques for suppressing CBET in frequency-tripled, Nd:glass laser beams crossing in a transonic plasma: a.) frequency detuning using two or three discrete “colors” of narrowband laser light; and b.) broad laser bandwidth. We find that for beams modeled with random speckle patterns, distributed phase plates and polarization smoothing, and for plasma conditions similar to those on the National Ignition Facility, the former method reduces CBET to an extent, but the degree of mitigation plateaus once the frequency separation greatly exceeds the resonance width of the CBET instability. Broadband lasers, on the other hand, are predicted to suppress CBET completely at a bandwidth of about 8 THz (Δ ω/ω₀ ≃ 1%, where Δ ω/2π and ω₀ are the laser bandwidth and angular frequency, respectively) for the same conditions. Although the Nd:glass lasers used for ICF research today have bandwidths far below this value, the spectra from such lasers could likely be broadened to multi-terahertz levels by utilizing stimulated rotational Raman scattering in a gaseous diatomic medium. Alternatively, the required bandwidth could be obtained with an excimer laser driver such as argon-fluoride, which has a native bandwidth in excess of 7 THz. Either of these two options would enable higher and more symmetric ablation pressures in future, direct-drive, ICF target designs.

由于跨束能量转移（CBET）而引起的激光散射是直接驱动惯性约束聚变（ICF）中不希望有的过程，该过程会降低内射靶的压缩和对称性。在这里，我们介绍了基于波的代码LPSE进行的激光-等离子体相互作用模拟的结果，该模拟探索了两种技术来抑制跨音速等离子体中三倍频越过的Nd：玻璃激光束中的CBET：a。）使用两个或两个频率进行失谐窄带激光的三种离散“颜色”；b。）宽的激光带宽。我们发现，对于以随机散斑图样，分布相板和偏振平滑建模的光束，以及与国家点火设施类似的等离子体条件，前一种方法在一定程度上降低了CBET，但是一旦频率分离大大超过了CBET不稳定性的共振宽度，缓解的平稳程度。另一方面，预计宽带激光器将在大约8 THz（Δ ω / ω ₀  ≃1％，其中Δ  ω / 2 π和ω ₀是在相同的条件分别激光带宽和角频率，）。尽管今天用于ICF研究的Nd：玻璃激光器的带宽远低于该值，但通过在气态双原子介质中利用受激旋转拉曼散射，此类激光器的光谱可能会扩展到多太赫兹水平。或者，可以使用准分子激光驱动器（如氟化氩）获得所需带宽，该驱动器的固有带宽超过7 THz。这两种选择中的任一种都将在未来的直接驱动ICF目标设计中实现更高且更对称的消融压力。