Effective control of laser-plasma instabilities (LPIs) is crucial for achieving high gain laser fusion. Early experiments employing long-wavelength lasers, such as the fundamental Nd:YAG laser and CO₂ laser, suffered from severe LPI, prompting mainstream fusion devices to adopt frequency-tripled lasers at 351 nm (3ω). Although 3ω lasers help mitigate LPIs, they are more prone to inducing damage to optical components due to their relatively low damage threshold. In contrast, the frequency-doubled lasers at 527 nm (2ω) despite exhibiting stronger LPIs, possess an optical-damage energy threshold more than twice that of 3ω laser, thereby reducing the risk of damage to optical devices. Moreover, their higher conversion efficiency from fundamental frequency light enables a larger achievable power compared to 3ω lasers.​

       Given that 2ω and 3ω lasers each have their own advantages and limitations, it is natural to consider combining a small fraction of 2ω light together with 3ω light to form a two-color laser, as a potential driver for next-generation fusion facilities [1-3]. This large frequency separation two-color configuration offers higher conversion efficiency and a higher optical damage threshold compared with pure 3ω drivers of the same total intensity. Most existing studies of LPIs driven by two-color light focus on cases with small frequency separation (δω/ω₀ <10%), where the coupling of LPI mainly relies on the direct coupling of the laser fields. In this presentation, we will introduce a few novel coupling mechanisms that we have recently identified for two-color drivers with large frequency separation [4-5]. Through these mechanisms, the two-color drivers can achieve lower LPI than pure 3ω drivers at the same total intensity, highlighting their potential for application in future high-gain fusion schemes.

References

[1] Zhanjun Liu, et al. Controlling stimulated Raman scattering by two-color light in inertial confinement Fusion[J]. Physics of Plasmas 24, 082704 (2017).

[2] Qingsong Feng, et al. Interaction of parametric instabilities from 3