The influence of sinusoidal density modulation on stimulated Raman scattering (SRS) reflectivity in inhomogeneous plasmas is studied using three-wave coupling equations, fully kinetic Vlasov simulations, and particle-in-cell (PIC) simulations. Through a numerical solution of the three-wave coupling equations, we find that the sinusoidal density modulation is capable of inducing absolute SRS even though the Rosenbluth gain is smaller than π, and we describe a region of modulational wavelength and amplitude in which absolute SRS can be induced, which agrees with earlier studies. The average reflectivity obtained by the Vlasov simulations has the same trend as the growth rate of absolute SRS obtained from the three-wave equations. Instead of causing absolute instability, a modulation wavelength shorter than the basic gain length can suppress the inflation of SRS through harmonic waves. In addition, the PIC simulations qualitatively agree with our Vlasov simulations. Our results offer an alternative explanation for high reflectivity in experimental underdense plasmas, which is due to long-wavelength modulation, and a potential method to suppress SRS using short-wavelength modulation.

使用三波耦合方程、全动力学 Vlasov 模拟和细胞内粒子 (PIC) 模拟研究了正弦密度调制对非均匀等离子体中受激拉曼散射 (SRS) 反射率的影响。通过对三波耦合方程的数值解，我们发现即使 Rosenbluth 增益小于π，正弦密度调制也能够引起绝对 SRS，并且我们描述了可以诱导绝对 SRS 的调制波长和幅度区域，这与早期的研究一致。Vlasov 模拟获得的平均反射率与从三波方程获得的绝对 SRS 的增长率具有相同的趋势。比基本增益长度更短的调制波长不会引起绝对的不稳定性，而是可以通过谐波抑制 SRS 的膨胀。此外，PIC 模拟定性地与我们的 Vlasov 模拟一致。我们的结果为实验性低密度等离子体中的高反射率提供了另一种解释，这是由于长波长调制，以及使用短波长调制抑制 SRS 的潜在方法。