Frequency chirp effects on stimulated Raman scattering in inhomogeneous plasmas

Mufei Luo (1, 2, 3) , Stefan Hüller (1) , Min Chen (2, 3) , Zhengming Sheng (2, 3, 4)

1 CPHT - Centre de Physique Théorique [Palaiseau]
2 Key Laboratory for Laser Plasmas (MOE)
3 Collaborative Innovation Center of IFSA (CICIFSA)
4 Tsung-Dao Lee Institute, Shanghai Jiao Tong

Previous studies have shown that the use of laser bandwidth may mitigate the growth of stimulated Raman scattering (SRS) in laser plasma interaction experiments, in particular when the spectrum of the driving (or pump) laser is composed of uniformly distributed frequency components with a well-chosen bandwidth [for example, M. Luo et al, Phys. Plasmas 29, 032102 (2022); H. Wen et al, Phys. Plasmas 28, 042109 (2021); R. K. Follett et al, Phys. Plasmas 26, 062111 (2019)]. Here, we investigate the effects of frequency chirp in the pump laser on backward SRS in inhomogeneous plasmas, taking into account kinetic effects associated with the nonlinear detuning of the parametric resonance due to high-amplitude electron plasma waves (EPW). Via theoretical considerations and numerical simulations, using a multi-dimensional particle-in-cell (PIC) code, it is shown that positive frequency chirp rates lead to a displacement of the resonance in the plasma profile. For a sufficiently strong positive chirp rate, such that the resonance displacement is faster than the EPW group velocity, the EPWs prove to remain limited in amplitude such that SRS is suppressed. The required frequency chirp rate corresponds to a laser bandwidth of about 1-2%.

Domaines: Physique des plasmas [physics.plasm-ph]

Mufei Luo, Stefan Hüller, Min Chen, Zhengming Sheng. Frequency chirp effects on stimulated Raman scattering in inhomogeneous plasmas. Physics of Plasmas, 2022, 29, pp.072709. ⟨10.1063/5.0096771⟩. ⟨hal-03706556⟩