Development of Lasers with Broad Bandwidth for LPI mitigation at NRL

Research at the Naval Research Laboratory pursues advanced lasers that can mitigate laser-plasma instabilities (LPI) in applications such as inertial confinement fusion. This presentation will discuss two main components of the current program: stimulated Rotational Raman scattering (SRRS) and Argon-Fluorine (ArF) excimer lasers. Stimulated rotational Raman scattering (SRRS) has been demonstrated on the Nike laser facility [Weaver, Applied Optics, 2017] as a path with potential application at existing laser facilities. Through a combination of high intensity propagation and control of the laser spectrum in the low-energy stages of the laser, the output spectrum of Nike has been broadened due to SRRS from an intrinsic 1 THz bandwidth to ~5 THz. This amount of bandwidth has been shown to be effective for mitigation of slow-growth instabilities, such as cross-beam energy transport (CBET) [Bates, High Energy Density Physics, 2020]. Target experiments using this capability are being planned. The development of Argon-Fluorine lasers [Wolford, High Energy Density Physics, 2020] is a more recent addition to the NRL program. This advanced system looks particularly useful for LPI mitigation due its short wavelength (193 nm) and potential for bandwidths approaching ~10 THz. The development effort at NRL's Electra laser facility has reached record output energies for an ArF system and has begun to evaluate the characteristics of the output spectrum for different modes of operation.